et Gey aa seal Hath " vit ‘ u iy htt J y “il ai mnie! “ore “ i SUG tg Ms } aie : ii ‘ne Abit i Ania Gai erat Wie etl cee MOPED Te tt bi if whit HEH! tn i, ni ue iii , tra Ph a sit iit ae aN a iti esl eat va & Di sit ihe Re Sti Fe, i! a ae a as bl iyty ty if \ tt nit H "s) ‘ ett ie ty Ln Hite fadhe ys ote te ; Ht ta \ He tt rt Wt Hine She ma 1.{ ag ty cet ee tpt Ho f pu ‘ Mee ea f uit Aah {A ee ti feeete fast i nt 3 a0 t ish rr) {tel Dene pate 34 be +t ye om SURVEY LIB! RARY Digitized by the Internet Archive in 2010 with funding from University of Illinois Urbana-Champaign http://www. archive.org/details/diseasesofsmallg35bo0ew N“ 27.0 lfGc "il Ups. ne 35 Cop.6 Hoag Diseases Small Grain Crops in Mlinais | GH. BOEWE et 2 oe OS UNIVERSIT Y OF ILLINOIS ¥ 2% ron ILLINOIS” Oy NATURAL ‘HISTORY, «som Be ce a? x) se OOK) on ws yt 5 Sagat eae | SUAWIE OP WII WINNS Henry Horner, Governor DEPARTMENT OF REGISTRATION AND EDUCATION John J. Hallihan, Director Diseases of SMALL GRAIN CROPS in DMinois G. H. BOEWE THE LIBRARY OF THE Wee CS yRVERSITY OF 1 U7" Printed by Authority of the State of Illinois NATURAL HISTORY SURVEY DIVISION Theodore H. Frison, Chief Circular 35 Urbana September 1939 STALE OF AL EAN OFS Henry Horner, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Joun J. HALiiHan, Director BOARD OF NATURAL RESOURCES AND CONSERVATION JouHN J. HALLIHAN, Chairman WILLIAM TRELEASE, D.Sc., LL.D., Biology Henry C. Cow es, Ph.D., D.Sc., Forestry L. R. Howson, B.S.C.E., C.E., Engineering Wi.tiaM A. Noyes, Ph.D., LL.D., Chem.D., D.Sc., Chemistry Epson S. Bastin, Ph.D., Geology ARTHUR CUTTS WILLARD, D.Eng., LL.D., President of the University of Illinois NATURAL HISTORY SURVEY DIVISION Urbana, [Illinois SCIENTIFIC AND TECHNICAL STAFF THEODORE H. Frison, Ph.D., Chief SECTION OF ECONOMIC ENTOMOLOGY W. P. Fuint, B.S., Chief Entomologist C. C. Compton, M.S., Associate Ento- mologist M. D. Farrar, Ph.D., Research Ento- mologist J. H. BicGer, B.S., Associate Ento- mologist S. C. CHANDLER, B.S., Southern Field Entomologist L. H. SHROPSHIRE, M.S., Northern Field Entomologist W. E. McCaurey, M.S., Assistant Entomologist C. J. WEINMAN, M.A., Assistant Ento- mologist C. W. Kearns, Ph.D., Research Fellow in Entomology ARTHUR E. RitcHeR, B.A., Research Fellow in Entomology R. C. RENptTorFF, M.S., Research Fellow im Entomology K. L. KniGut, M.S., Research Fellow in Entomology SECTION OF INSECT SURVEY H. H. Ross, Ph.D., Systematic Ento- mologist Cari O. Monr, Ph.D., Associate Ento- mologist, Artist B. D. Burxs, Ph.D., Assistant Ento- mologist G. T. RIEGEL, B.S., Assistant Entomolo- gist KATHRYN M.SOMMERMAN, B.S., Artist, Assistant Entomologist SECTION OF FORESTRY James E. Davis, M.F., Extension Forester LEE E. YEAGER, Ph.D., Forester SECTION OF AQUATIC BIOLOGY Davip H. THompson, Ph.D., Zoologist GEORGE W. BENNETT, Ph.D., Limnologist D. F. HANSEN, Ph.D., Assistant Zoologist C. L. SCHLOEMER, Ph.D., Assistant Aquatic Biologist SECTION OF GAME RESEARCH AND MANAGEMENT Ractpu E. YEATTER, Ph.D., Game Specialist C. S. SPOONER, JR., M.S., Junior Biolo- gist SECTION OF WILDLIFE EXPERIMENTAL AREAS ArtTHuR S. HAwKINs, M.S., Game Technician F. C. BELLROSE, JR., B.S., Assistant Game Technician COOPERATIVE WILDLIFE RESTORATION PROGRAM (State Department of Conservation and U. S. Biological Survey) H. G. ANDERSON, M.A., Junior Biologist Louis G. Brown, B.S., Junior Biologist R. E. HEssELSCHWERDT, B.A., Junior Biologist SECTION OF APPLIED BOTANY AND PLANT PATHOLOGY L. R. TEHON, Ph.D., Botanist D. B. CREAGER, Ph.D., Research Pathologist J. C. Carter, Ph.D., Assistant Botanist G. H. BoeweE, M.S., Field Botantst SECTION OF PUBLICATIONS James S. Ayars, B.S., Editor This paper is a contribution from the Section of Applied Botany and Plant Pathology (83842—3500—6-39) ae my culicsgen 2 Contents PAGE [ENtinerOis Cereal DISCASeS ays. «sts. cicit cereals tcl eter o Wem olvere seit History of plant diseases, 2; Kinds of plant diseases, 2; Fungi, bac- teria and viruses, 3; Dissemination of diseases, 7; Damage done by plant diseases, 8; Important cereal diseases and their causes, 10; How to recognize diseased plants, 11; How to diagnose a plant dis- ease, 12. MIMAVVING Atm DISEASES imine ay os cote roe ie ACIS ae) con ee Sse elaine eee HE LV: Diagnostic Key for Wheat Diseases............................. ILGEIP LETS a os Bi dcastice os Dc ce nOtEReh OCR HOIS SIE NEC chek Gh MIPIM Ie ie ana en Od BIACKES CEMPRUS tac e sere rR eee ee enetee Rae nis a Pra eee ee Speckled@elieatmislote hiss ..a5.cace.cs Acti oi akg See eee RE ee TE a oe SUBEID 'o: 6.105 CBX BION CREE RCE aE COLE TN Rann er tee eS a Se ashe a PAIGE ACTIOSE Pt its yore co AIL APA CH ena EONS) TIGRE E RELLY 5 AE ee Melminthosporium: Disease... 2... 4.2.60 ne ee ee ee lees « SUIT ATITG? SITTIN asco asree ence ne ce ake eck CIR RL A ie eats a rare ee NS ren eM THO OS CMO IRUUCe iE Mice aes sare ofa xc sie ree SOR Sie eee ee LA erigce RSSTOETT Toi 62ers Ste ay a cea sane rea me A AS alm GIVE tl = Sct t ce hay heli cate ord Mocs Seek Male A oat Peo oe oes Fahim Gaile eee eect cite crower ey ah soe ahs 1b See) Bien cutemapeeat eewanaame aeons (CUO: LEGG Ua cd Spbecrmeaco net can tokens eee oR Son ASE MANES Aci eee owe ersvan Vil Gyre Sees exes cho eet ase once hE es eG) eae nuSee en Ashes NWO Sal Creer eee ne ee el Ny ren yer woe hegs ee Seta 2 Ch PE ae ye oe THE ova a, Sa ith oe eet gaat oe ne ARO ee Se era, nce INEM AOC eRDISCAS Ce rreet cious ta tea eee eH, Suse hoes eee eine be eas COAtCSADISCASES ee ere eck re Pee nce oe Sates ete Sle a ta tas CIES ee eee es Diagnostic Key for Oats Diseases................... 0.0 cee eee CO Wie FUUS Gee = 8 oa eee rer Pete e cms eae .0 Grees Gans 6 waeeta BME mane Sew RS Blaeke Ste ini RUSE ses ee ce castors oy Fae pe cian eS RO Cee Oe DERI IS Oe SNe La) Ky” LES) eee as ee ete Sceea CRC Ac ISMN ROCESS Ion, B icteric eematorc Melminthosporium: Weaf Spot. 3.5... .c.02 2s oeee es bee ee celles sees SS CADE ees eee Sao oid ous Oe CMe OLY Suse Oe ate PATTEM ACM OSC rica sted aires nae Near eware eed nie Sale ce sawckahc ave di er Sh auauai ae baicpe Bes ME GOSE Me SIMU bre pee stews a temci aeet oda es euaicor ns. wh a aN iNaan vaprt tenance tysuctercehatne WG veredee S Utes ok eo eere ae CREST eae A Een To GIS? a oue suse) CEASE | 33 ESTE a: oon! a BREREMAM eta tes SWE Sencar gO ECE aCe rer Alea AL SRS a Sane CIR Seater Pitan Eee a LDTREXDLY G: Gd ates DG ORR RR Sain hee Oe IO oR en ete athe eh PC res abs AP eerie Owdenyae Vil de wierd ole ae ate Tee Arle VMUISCASES oer ea iseaienen te cake sreee tokens ods Ske ae Eta lniete woe Remnoree Diagnostic Key for Barley Diseases.....................--seeee- 1 LSE PAT RATS te SA Pens EG SRE SS eee en Coe Sr Say eee ig mime oe Led EOE Sir SL TIC] han eae rico enc ahem canes Comienc cae tr cRtiCeinns coombesoycscterenre SLT NO oe Gis te oe a BE Bo Cs IR RRS EONS CRre SER a ce ir sochere Bacterial lich ter ce oie ee ea Stee red Se tee ee or ecenet es Spot@Blotelitescr reece eee oat ahe cote ere soe Neate exe cscs tienes INGE Cas es Ot Chae eee ee ee cane cee bh sae orcs ayrey ore ieareeue wenger epee 1 INon-Parasitic Brown Spot.0s+ .c<-ese- + oo. ee 87 SCA ae J skis, ah pid GS A ond MS oon Ae 88 ANENTACHOBE e065 5 eee 2 iets Dies eieod ed the ee eae akee Ole oe 90 Loose (SmiUs oe See oe a ag Me bie bs ae ne ee eee 90 Covered Smut. i904 se eo we eee 92 Powdery Mildew? i. 0 oe ee ee eee 94 | DC eee AG POU OR ea ee a GE REDS 95 V.. Rye -Diseasesii oni. 30s oe i oot ee ee eee tena. se eee 96 Diagnostic Key for Rye Diseases... .. 02:2. .52)5. 25.52 ee eee 96 Tueaf WRuStiy os. dn rns Maas ea Se ee ok ee 98 Black Stem “Rust:... 3.0.5 54 ate ots a then beak eee 99 SGalldlssccreco hoa cl acd oe ait eer eine dee ager y es 100 Bacterial- Blight; sect. oc json oe oo ae oc ns 7 n8 ee eee 101 Scabi.. ae deco a B stiee Oe 5 te es oe EON BL See 102 AmthTraAcCnNOSE:s 22 selie.3 Ge. sacle ere sphlelahey Seed 3. s02- Sah skool 103 Helminthosporume Disease... 45255) ee 103 Stem: Smut 2) 5 ache 6b eens cova eka: oe gs See eee 103 Loose Smutic., 20 aay oe he 05 ow Same ea cee eee 105 IP COCLS 2 hos oy ae eee cle erevestoe ss Wn suse eve Medios Soon 106 Powdery Mildew: «cS S58 face os ose ceed, Oo Ss 107 IMIOSATEG:. OoSshasahaccse Mates oe ee ess era ee nese LOS Nematode Diseases i052. kes one as GL anes eee 109 VIE ‘Cereal’ Diséase Controls oiac0.0 2. secs 6 ena ts hcl eee. eee 110 Good farm practices, 111: Sanitation, 111; Rotation of crops, 112; Resistant varieties, 112; Cultural methods, 113; Good seed, 114; Fungicides on the growing plant, 116. Regulation, 116: Inspection, 117; Quarantine, 117; Eradication, 117. Seed treatment, 118: Seed treatment suggestions, 118; Machines for applying dust treatments, 120; Copper sulfate treatment, 121; Copper carbonate treatment, 122; Formaldehyde treatments, 123; Hot water treatments, 126; Organic mercury treatments, 128. Photographs by Ray R. Hamm, unless otherwise credited; graphs by Ronald E. Favreau; figure 1 by Kathryn M. Sommerman. Natural History Survey Publications of Value te Mlinois Farmers Peach Yellows in Illinois. By L. R. Tehon and G. L. Stout. Illinois Natural History Survey Circular 21. 24 pages, 9 figures. November, 1929. Windbreaks for Illinois Farmsteads. By J. E. Davis. Illinois Natural History Survey Circular 29. 18 Pages, 12 figures. April, 1938. Outwitting Termites in Illinois. By W. E. McCauley and W. P. Flint. Illinois Natural History Survey Circular 30. 19 pages, 19 figures. June, 1938. The Peach Tree Borers of Illinois. By S. C. Chandler. Illinois Natural History Survey Circular 31. 36 pages, 22 figures. January, 1939. Controlling Peach Insects in Illinois. By S. C. Chandler and W. P. Flint. Illinois Natural History Survey Circular 33. 40 pages, 32 figures. August, 19393 Rout the Weeds! By L. R. Tehon. Illinois Natural History Survey Circular 34. 47 pages, 13 figures. August, 1939. The Effect of Petroleum-Oil Sprays on Insects and Plants. Illinois Natural History Survey Bulletin 21, Article 1. 32 pages, 21 figures. November, 1936. Publications of General Interest Fieldbook of Illinois Wild Flowers. By the staff. Illinois Natural History Survey Manual 1. 406 pages, 349 figures, color frontispiece. Descriptions of 650 species. March, 1936. $1.50. Fieldbook of Illinois Land Snails. By Frank Collins Baker. Illinois Natural History Survey Manual 2. 166 pages, 170 figures, 8 plates, color frontis- piece. Descriptions of 122 species. August, 1939. $1.00. Pleasure With Plants. By L. R. Tehon. Illinois Natural History Survey Circular 32. 32 pages, 9 figures, frontispiece. April, 1939. Lake Management Reports 3. Lincoln Lakes Near Lincoln, Illinois. By David H. Thompson and George W. Bennett. Illinois Natural History Survey Biological Notes No. 11. 24 pages, 8 figures. August, 1939. Address orders and correspondence to the Chief ILLINOIS STATE NATURAL HISTORY SURVEY Natural History Bldg., Urbana, III. Payment in the form of U. 8. Post Office money order made out to State Treasurer of Illinois, Springfield, [llinois, must accompany requests for those publications on which a price is set. Stinking smut of wheat. The two heads in the center are infected; those to the right and left of them are normal. Kernels in the lower row are normal; those in the upper row are infected and often are called smut balls. Harvested grain containing even a small percentage of smut balls is subject to price dockage. I Nature of Cereal Diseases \NMALL grains, from an economic standpoint, are among the SB chost important crops raised on Illinois farms. They occupy an essential place in the cropping system and, besides having a market value, they provide food for animals, serve as pasture and bedding, and sometimes as green manure crops. All of the small grains, the most important of which in Illinois are wheat, oats, barley and rye, are susceptible to attack by diseases. Since 1921 the Illinois Natural History Survey has been engaged in surveying the grain fields of the state to ascer- tain what diseases are present and to determine the relative prevalence and intensity of attack of the epidemic diseases. That accurate data might be obtained, counts have been taken yearly in representative fields and, in case of doubt as to the identity of any disease, samples have been given laboratory examination. As a result of these surveys, the economic importance of the diseases of cereal crops has been defined more clearly than in the past. These diseases affect the farmer’s income not only by reducing yields but also by reducing the quality and conse- quently the market value of the grain harvested. Data collected annually over a period of 10 years show that in Illinois leaf rust alone, which is the most important disease of wheat, attacks on an average 93.9 per cent of the wheat plants and destroys 14.98 per cent of the wheat leaf area. The average loss per year from this one disease, indicated by estimates for 20 consecutive years, is $1,616,000. With such losses incurred annually from this and other diseases, it is important that the farmer be able to recognize and combat the diseases that are most prevalent and destructive. The more conspicuous diseases, such as rusts and smuts, are well known to many producers of grain; but there are other important diseases, which attack roots or stems or destroy part of the leaf area, that are not so generally known. A detailed description of the cereal diseases that have been found important in Illinois, and of suitable control methods, is presented in the following pages. Diseases are listed under the cereals they attack. If a disease attacks more than one crop, it is described most fully in relation to the crop on which it is most important. Cross [1] 2 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 references are given in every case, so that a reader may turn to the full description. A key based on host plant symptoms has been inserted at the beginning of each section devoted to a grain, to enable the reader to identify diseases in which he may be inter- ested. HISTORY OF PLANT DISEASES Plant diseases have occurred, and some have been recog- nized, since the earliest days of man’s civilization. Records of blights and mildews are found in early historic and religious writings. Rusts were recognized and mentioned by Aristotle as early as 350 B. C. But ancient peoples knew little of the physio- logical behavior of plants, and maladies were regarded by them with superstition and were often thought of as plagues sent as punishment by some divine power. Such ideas persisted through the ancient eras and into the Dark Ages. Modern knowledge of plant diseases may be said to date from 1853, with the publication of the brilliant studies of the German scientist, Anton de Bary. Until the beginning of the present century, German scientists held the most prominent place in the development of plant pathology. In 1873, the first teaching of plant pathology in America was done at the University of Illinois, by Professor J. T. Burrill. With the organization in 1885 of a section of mycology in the division of botany of the U. S. Depart- ment of Agriculture and the organization in 1887 of the state agricultural experiment stations under the Hatch Act, a broad foundation was laid for the study of plant diseases in the United States. Since that time much has been learned about causes and methods of control for many plant diseases, and because of its contributions the United States has attained a preeminent place in the field of plant pathology. KINDS OF PLANT DISEASES In the process of growth, plants may be subjected to physio- logical disturbances, to attack by parasites or to virus infections. All of these interfere with normal functioning or development, and the abnormal conditions that result are known as diseases. Disease may be localized in a definite part of a plant, such as the roots, stem, leaf, flower or grain, or the entire plant may be affected. BOEWE: DISEASES OF SMALL GRAIN CROPS 3 According to cause, diseases of plants may be divided into the following three groups. Parasitic Diseases.—Plants are subject to attack by animals and by other plants which depend for their living upon the plant they attack. All animals that depend in any measure upon plants for food may be regarded as in some degree parasitic. Among those that injure useful plants are gophers and mice, insects, snails and nematodes. Parasitic plants include seed-bearing plants such as dodder, mistletoe and broom rape, and non-seed- bearing plants such as fungi, algae, slime molds and bacteria. Attack by fungi and bacteria, which generally live internally in their host plants, usually results in the production of disease. Non-Parasitic Diseases.—Non-parasitic diseases may be due to a number of causes, of which the most important are improper environmental conditions, lack of certain resistant factors in the plant and harmful mechanical influences. Proper soil conditions, temperature, rainfall, light and air are essential for normal development. Lack of the correct kind or amount of one or more of these factors, or a disturbance in their balance, may lead to the development of disease as certainly as does attack by para- sites. Resistant varieties have been developed which may attain normal growth in spite of some adverse environmental factors; lack of resistant factors tends to make plants susceptible to disease. Mechanical injuries to plants may produce disease and may also open avenues for infection by parasites. Virus Diseases.—Virus diseases are systemic infections which invade the entire body of a plant. They result in various kinds of abnormalities, the commonest of which, a mottling of leaves with light and dark green, is the only type known on cereals. But other kinds of plants show other effects, such as the bushy growth of asters affected by aster yellows and the willowy growth of peach trees infected with peach yellows. Leaf mottling is commonly called mosaic. FUNGI, BACTERIA AND VIRUSES Fungi.—Fungi are members of a primitive group of plants. They do not contain green coloring matter and so are unable to produce their own food. They may be divided into two classes: parasitic, depending on living plant tissue to maintain their existence, and saprophytic, living on dead plant or animal mater- ial. Most parasitic fungi are detrimental to man, but those that 4 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 are saprophytic may be beneficial by aiding in the disintegration of dead plant and animal material and thus maintaining the fertility of the soil. Fungi, though very much smaller and simpler, are compa- rable in some ways to green nlants, fig. 1. The part of the fungus which corresponds to the root, stem and leaves of a green plant consists of threads or filaments called hyphae. Hyphae usually are divided into cells by cross walls, and they usually branch and rebranch, forming a network of filaments. The mass of hyphae which makes up this network is called mycelium. In a fungus, as in seed plants, a vegetative period concerned with growth and the accumulation of food precedes the repro- ductive phase. The vegetative part of a parasitic fungus, the mycelium, usually grows within the host plant’s tissue and is not often visible on the surface; but it may be superficial, estab- lishing contact with the interior of the plant by means of small suckers which it pushes into the outer cell layer of its host. It is the reproductive structure of the fungus, correspond- ing to the fruit and seed of flowering plants, that we most commonly see. Such a “fruiting” body is usually dark and large enough to be seen with the naked eye. It may be produced on the surface of the host, but usually it is formed within its tissue and breaks through to the surface by the time the spores it con- tains, which function somewhat like seeds, are mature and ready to be discharged. A spore differs from a seed in that it does not contain a tiny embryo or young plant. It is very small, often being made up of only one cell, but it contains the living material by which a fungus is reproduced. If a spore has more than one cell, each cell usually has the power of producing a new fungus. Different kinds of fungi produce their spores in different ways. Some send up stalks from the vegetative part, on which the spores are produced singly, in strings like beads or in clus- ters. In the last case, the spores may be inclosed by a membrane or may be exposed. Other fungi produce their spores on small stalks inclosed in flask-shaped or spherical bodies, in more or less Fig. 1 illustrates the life history of wheat compared stage by stage with life histories of four important fungous parasites of grains. The wheat seed and the overwintering spores, pictured across the top of the page, germinate and give rise to primary structures such as seedlings and germ tubes, in the second row. Growth forms the vegetative stage, in the third row, which in the case of the fungi constitutes the period of infection. Finally the wheat plant and the fungi mature, as in the fourth row, producing seed or over- wintering spores. Details of individual life histories are given in the text. BOEWE: DISEASES OF SMALL GRAIN CROPS 5 POWDERY LOOSE STEM %. aire ! Zz Z a Ke = GE = ~ S <= g—< SRG —< Fig. 1—Four typical life histories of fungous parasites of cereals compared with the life history of wheat. 6 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 flattened ‘‘cups’” or in small club-shaped sacks which are pro- duced inside spherical bodies. As a rule spores are so very small that they are invisible without a microscope, but they are pro- duced in immense numbers. It has been estimated that there are at least 1 million, possibly as many as 8 million, spores in one smut ball of stinking smut. Some fungi produce only one kind of spore, and this often is called a summer spore. As seeds of higher plants vary in their length of viability, so do spores. Many summer spores are unable to withstand winter conditions, and many fungi therefore de- velop a second type, called the resting spore, which serves to carry the fungus through the winter. Newly formed spores may remain attached for a short time to the structure on which they are borne, but soon they are discharged and carried away. Only a very small percentage of the spores that are produced ever cause infection, because most of them alight in situations that do not furnish the food material and moisture necessary for their development. Some fungi find suitable food material in only one host plant, but others not so specific in their requirements thrive on two or more host plants. In some instances the host plants of disease-producing fungi are unrelated, as is true of barberry and wheat in the case of black stem rust. Weeds as well as cultivated plants may serve as hosts. Moisture is necessary both for spore germination and for enabling the young fungus to enter its host. Usually when the fungus has once entered its host it is able to continue its exist- ence, for there it finds ideal moisture conditions and comes in close contact with the source of its food, which it absorbs directly from the cells of its host. However, many spores die because they fall on unsuitable hosts, from which they are unable to obtain food for growth, or because they do not find sufficient moisture to enable them to germinate or because after germinating they dry up before they have a chance to enter the host. Bacteria.—Bacteria are the very minute one-celled plants commonly called germs. They are almost inconceivably small, measuring as an average only about 1/12,700 inch in length. It would take 793 of them placed end to end to measure 1 16 inch. There are three general forms or shapes of bacteria, namely, spheres, rods and spirals. Only the second causes disease in plants. Bacteria have the simplest kind of life cycle. A mature ~] BOEWE: DISEASES OF SMALL GRAIN CROPS bacterium divides into two nearly equal parts, and each part grows to the size of the original and repeats the division if con- ditions are favorable. The rate of division and growth depends upon such environmental factors as food available, temperature and presence or absence of poisonous substances, but under favor- able conditions a life cycle is completed in 30 to 40 minutes. While certain bacteria form spores which carry them through periods of adverse conditions, none of the bacteria that cause plant diseases are known to have this adaptation. Viruses.—The infectious principle that causes mosaic dis- eases is called a virus. What it is, no one knows. It has some of the characteristics of a germ, but it is so small that it cannot be seen with even the most powerful microscopes. Nevertheless, viruses can be transferred from diseased to healthy plants, after which the healthy plants become diseased. Insects are the chief carriers, but man is an important agent, also, in spreading cer- tain virus diseases. Some viruses can be transmitted by seed; others are thought to reside in the soil. DISSEMINATION OF DISEASES Bacteria, fungi and viruses are carried from place to place by various means. In the case of bacteria, the entire individual is transferred, while generally only the spores of fungi are moved. In what state viruses are carried, no one knows. The most important disseminating agents for fungi and bac- teria are wind, water, insects, animals and man. Bacteria and spores of fungi have been known to be carried long distances, in some cases hundreds of miles, and retain their viability. Strong winds may carry fragments of infected plant debris. Water may aid in disease dissemination in several ways. Plant material is carried for long distances down rivers, around the shores of lakes or along the ocean shores. Accompanying this debris are bacteria and fungi which, when the material drifts to shore, may become established on crops. Rain is often instrumental in washing bacteria and fungous spores from one plant to another; however, this means of dis- tribution is limited in its importance. Running water may carry infected soil and plant debris from one field to another and thus spread both soil-borne and air-borne diseases. Insects play a very important part in spreading parasites and viruses. The hairy bodies of insects are well adapted to 8 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 picking up from diseased plants spores and bacteria which are dropped as the insects travel from plant to plant. The mouth parts of sucking insects feeding upon diseased plants become contaminated with bacteria or spores, which are subsequently deposited on healthy plants. The majority of viruses are trans- mitted by insects, and some of them can be transmitted in no other way. Animals also may aid in the distribution of plant diseases. As they move through the fields, they may rub off on healthy plants the spores they have picked up on their coats from dis- eased plants. There are many instances of the introduction and spread of diseases by man. Seeds, bulbs, nursery stock and other plant materials shipped from country to country, state to state or farm to farm occasionally carry invisible infections to new localities. Infected plant material used as bedding or packing, when shipped from one place to another, may disseminate disease-producing organisms. As an illustration of the local distribution of disease through man’s activities, we may cite a case observed in Illinois of a cer- tain farmer and his four neighbors. In 1932 this farmer had stinking smut in his wheat. His neighbors had clean fields. At harvest time, the machine threshed the first farmer’s wheat and then went on to his neighbors. Each farmer used wheat from his crop for seed, without treating it before planting. The next year the four neighbors found smut in varying amounts in their fields. When the first farmer’s wheat had been threshed, spores of the smut fungus were left in the machine and were later mixed in his neighbors’ wheat, the greatest number of spores being mixed with the wheat of the first neighbor to use the machine and the smallest number with that of the neighbor threshing last. Other implements, such as rackwagons, drills and cultivating tools, sometimes carry infection from field to field or farm to farm in somewhat the same way. DAMAGE DONE BY PLANT DISEASES Diseases cause very definite losses by decreasing stands, lowering yields and impairing the quality of grains, fig 2. Less definitely determinable but very important are the attendant increases in cost of production, lowering of market values and, in extreme cases, decreases in land values. BOEWE: DISEASES OF SMALL GRAIN CROPS ) The yield expected from an otherwise normal cereal crop may be greatly lessened by the presence of disease. Some dis- eases, by killing the plants they infect, cause poor stands. Vile KGINeS Oi 7b AIRS SO) 2 4 r4t less GIS ZO) ye) 2 eh 216) MMM BARLEY & RYE ee Weeatetatatetetatetatenetetates Fig. 2——Money value of the reductions, due to disease, in cereal crop yields in Illinois, based on the estimates available for the period 1926-1937. Others, that attack only portions of the plants, such as roots, stems or leaf tissues, so weaken the plants that they produce less grain. Plants with roots attacked by rot fungi or with a portion of the leaf tissue destroyed usually produce grain of inferior quality, which brings a lower price than first quality grain. If this poor grain is kept for seed, a reduced stand, poor yield and inferior grain may be expected the following season. A reduc- tion in yield, together with an increase in the amount of seed required to produce a good stand, at once increases the cost of production and decreases the net returns a farmer may expect from his grain crop. All of these factors may combine eventually to lower the value of the land, especially if the principal damage is due to a disease which remains viable in the soil from year to year. 10 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 25 IMPORTANT CEREAL DISEASES AND THEIR CAUSES Diseases of crop plants noticed by observant persons receive names that’ are descriptive of their appearance and, by long and general usage, these common names come to have definite and universal significance. Scientific investigation eventually re- veals the cause of the disease, and if the cause is a living organ- ism it is named by the scientist in Latin, so that the meaning of the name may be understood throughout the world. The Latin, or scientific, names of the parasites that cause the diseases of cereal crops discussed in succeeding pages are given below, with the authorities responsible for them. 1 Smut diseases: Loose smut of wheat and rye........ Ustilago Tritici (Pers.) Rostr. IL@OREG HoT OLE OBS sdccausacussescc: Ustilago Avenae (Pers.) Jens. ILO Siambie Ot loWAly. oc ococeeo000Ke Ustilago nuda (Jens.) Kell. & Sw. Coveredusmutmotsoatseame eee Ustilago laevis (Kell. & Sw.) Magn. Covered smut of barley............ Ustilago Hordei (Pers.) Kell. & Sw. Stinkine smut of wheats. ee asec Tilletia laevis Kuehn niles STM OIE WANG goose scascccece Urocystis Tritici Koern. SHG SMe OH TAYE oocceacodsvgauecac Urocystis occulta (Wallr.) Rabenh. 2. Rust diseases: F ILGANE TWIG Oil WHEE. oon coscocccese- Puccinia rubigo-vera (DC.) Wint.. var. triticina (Erikss. & Henn.) Carl. IDGRRE TEUISIG OE OMSlo oo onnccccocoouece Puccinia coronata Cda. IL@ERe TOI Gut lH co coop as doso oe Puccinia anomala Rostr. ueak Tusitiot< ty Claes coe siete ci eictereiereie Puccinia rubigo-vera (DC.) Wint., var. Secalis (Erikss.) Carl. Black stem rust of wheat, oats, loendlany Eyal IAW con coadodeccouvoc Puccinia graminis Pers. 3. Leaf diseases: Bacterial blight of barley.......... Bacterium translucens Jones, John- son & Reddy Bacterial eblichitvotenye eerie tte Bacterium translucens secalis Red- dy, Godkin & Johnson Barley, Stripe <2... kasi emcee Helminthosporium gramineum Rabenh. Isle} lolbislas, Git GBUSs ob occccuccosuut Bacterium coronafaciens Elliott Helminthosporium leaf spot of oats. .Helminthosporium Avenae Eidam INeteblotchohsbanleyenceneeee ees Pyrenophora teres (Died.) Drechs. Powdery mildew of all small grains. .Hrysiphe graminis DC. Scaldiioienvetots her... teeter oe Rhyncosporium Secalis (Oud.) Davis Speckled leaf blotch of wheat....... Septoria Tritici Desm. Spot blotchy oh wbanley we. cee eer Helminthosporium sativum Pam. 4. Head diseases: Basal glume rot of wheat.......... Bacterium atrofaciens MeC. BlackrchatinolunwinCeiuerersrercres serene rretere Bacterium translucens Jones, John- son & Reddy, var. undulosum Smith, Jones & Reddy 6. BOEWE: DISEASES OF SMALL GRAIN CROPS 11 Ergot, of rye and other cereals..... Claviceps purpurea (Fr.) Tul. Glume blotch of wheat............. Septoria nodorum Berk. Scab, of all small grains........... Gibberella Saubinetii (Mont.) Sace. Stem diseases: AMINA CTLOSCleieic is Ghee ties sive wae stone 8 Colletotrichum cereale Manns Nematode diseases... ic. s.0 cece. Tylenchus tritici (Stein.) Bast. Root rots: Malke-all’ of wheat... 2.0. s6ecse ns ees Ophiobolus Cariceti (B. & Br.) Sace. Foot rot of wheat and other cereals. .Helminthosporium sativum Pam. HOW TO RECOGNIZE DISEASED PLANTS Because of the wide prevalence of plant diseases and the great losses they cause, it is important to be able to recognize and deal with them. Plants that are diseased usually exhibit abnormalities, and from these it is frequently possible to deter- mine what disease is present. The following signs, or symptoms, occurring singly or in varying combinations, indicate the pres- ence of disease. il. 2. 3. When the entire plant is affected there is: a. Premature dying or ripening, usually accompanied by whitish or reddish-brown discoloration; or b. Dwarfing, often accompanied by a sickly yellow rather than a healthy green color; ov e. Extra growth, usually elongation of stems, with poor color, small leaves and weak stems. When the head is affected, there is: Pale or blue-green color and distended chaff; or Pinkish or reddish color on the spikelets; or Premature ripening of spikelets; or Abnormal roughening of grain; or Failure to head; or Grain replaced by: (1) Large purplish bodies (ergot); or (2) Short, thick galls, easily crushed, with fishy odor (stinking smut); or (3) Short, thick galls, hard, with no odor (nematode); or (4) Black powdery masses covered by delicate membranes (covered smut); or (5) Black, powdery masses not covered by delicate membranes (loose smut); or (6) Loose black masses dispersed before harvest (loose smut). When the leaves are affected, there may be: Water-soaked, sunken spots (bacterial spots); or Mottling or streaking with yellow (mosaics); or Brownish or reddish spots, usually dead (leaf spots); or Whitish-gray mold on surface (powdery mildew); or Brown longitudinal stripes, along which leaf splits (barley stripe); or Stripes of various colors, not accompanied by splitting; or Pustules on leaves (rusts). pHoaooe Pr ene ons gq fh 12 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 4. When the stem is affected, there may be: a. Black or purplish blotches, especially at joints (anthracnose, etc.) ; or b. Small elevations, red or black pustules (rusts); or c. Rot at ground line (seedling rot, damping-off ). 5. When the roots are affected, there may be: a. Reddish-brown or black spots on the roots; or b. Rotted, brittle roots (root rots). HOW TO DIAGNOSE A PLANT DISEASE When signs such as those listed above have been observed, the next step is to determine the specific disease that is present. To accomplish this it is necessary to analyze the symptoms in a logical manner, in much the same way as a physician diagnoses his patient’s ills. An analysis of the symptoms of disease is given for each crop, on later pages, in an outline form called a diag- nostic key. Before an attempt is made to use such a key, the outstand- ing symptoms exhibited by diseased plants should be carefully observed. It is desirable that a number of plants be examined and that the symptoms present in the greatest degree be noted. Because individual plants exhibit variations in symptoms, if only one or two plants are observed, incorrect diagnosis may result. In most cases it will be found that only one part of the plant has been affected—the head, leaves or some other part. For this reason, the key stresses first the part of the plant affected and refers by number to subsequent sections of the key, in which further analyses are given. In each such section, just two items are listed. Both of these should be considered and the outstanding symptoms previously noted kept in mind in making a decision as to which one applies to the case in hand. An item which describes only part of the symptoms refers by number to a section farther along in the key. But an item which, with the items above, completes the description of the symptoms gives the name of the disease at the end of the line. Analysis of symp- toms thus proceeds step by step through succeeding sections of the key until the identity of the disease has been worked out. The following is an example of the way in which a key is used in diagnosing diseases. In a well-grown wheat field, it might be noticed that the plants in a certain area seem less healthy than those in other parts of the field. A closer examination of these plants may reveal the chief sign of disease to be a spotting of the leaves. BOEWE: DISEASES OF SMALL GRAIN CROPS 13 The spots, it is found, are circular to long oval in shape and are covered by a grayish-white mold that can be rubbed off easily. The diagnostic key for wheat diseases on page 15 begins by separating diseases of seedlings from diseases of older plants. Since the wheat in this field is well beyond the seedling stage, we follow the statement, “Older plants diseased,’’ to section 4 of the key. Here diseases of vegetative and of fruiting parts are separated, those of vegetative parts being referred to section 5. Under 5 we find definite reference in the second statement to discolored spots, and this takes us to section 8. There the fact that our disease is on leaves takes us on again to section 15, but since we find no pustules we must proceed, as directed, to section 16. Here the reference to discolored spots on leaves sends us on to section 17, in which we find that the first statement, “Spots thinly covered by a superficial, powdery mold,” exactly describes What we have observed. So we know that the disease that has attracted our attention is powdery mildew. A check on the accuracy of a diagnosis may be made by turning to the description of the disease in the text. If the de- tailed description and the picture given there agree with what has been observed, the determination is correct. If not, it is advisable to start at the beginning and work through the key again. In different diseases, symptoms sometimes may be so similar as to cause confusion, resulting in an erroneous diagnosis. It is important to keep in mind that both items in any one sec- tion of the key must be considered before deciding which applies to the case at hand. Some diseases of plants are so difficult to diagnose from external symptoms that it is impossible for the grower to arrive at a determination from the use of a key. In such cases, the services of an expert plant pathologist are necessary. In sub- mitting samples to an expert, the grower should include three or four representative specimens showing the typical diseased condition, since it is often difficult, if not impossible, to make a definite diagnosis from a single specimen. It is advisable to sub- mit entire plants, including roots, since the disease may have originated in a different portion of the plant from that in which symptoms are noted. Specimens should be submitted in as fresh a condition as possible, but moisture should not be added as it tends to stimulate mold growth. Material usually reaches the expert’s laboratory in good condition if it is wrapped first in oiled paper and then in heavy wrapping paper. Il Wheat Diseases In Illinois the wheat crop is subject to attack by 33 recog- nized diseases. Not all of these are widespread or important, but it has been estimated that in 12 recent years those that are widespread and commonly destructive have brought about a re- re Dee habeas ge map 5 © 1,664,000] (aa aa a a C7) 15 485,000} 1928 851,000 1929 1802,000 1930 988,000 193 3,030,000 eee) = eee) 1932 3,214,000 1933 1934 4,655,000 Fig. 3.—Estimated reductions in Illinois wheat yields, 1926-1937, due to disease attack. The average annual reduction for the years represented is more than 3,500,000 bushels. duction in yield amounting to at least 42,557,000 bushels, an average of more than 3,500,000 bushels per year, fig. 3. While much of this apparent loss could not have been prevented, since no practical means have existed for controlling some of the most destructive diseases, much of it could have been avoided had [14] BOEWE: DISEASES OF SMALL GRAIN CROPS 15 known methods of combating certain diseases been in general use. The descriptions on the following pages deal mainly with diseases that are common and widespread, but a few now local in occurrence or apt to invade Illinois are described because of the importance they might have in the future. DIAGNOSTIC KEY FOR WHEAT DISEASES 1. Seedlings diseased CEB LAMUSs CUSCASCOR m5, haat ty En aial 9 eoeetea tions 0 kOe ane ned ee 4 2. Seedlings rot off at the ground line i petal FOV CT <8 uskesen ces ternierSo cee Helminthosporium disease, p. 33 Seedlings exhibit other symptoms of disease..................... 3 3. Seedlings are at first stunted and later turn yellow and die; their roots are rotted, reddish brown and sometimes covered with gray or pink mold.............. Scab, p. 28 Seedling leaves are rolled, twisted, curled or other- MUI SeaGUSLORLEG cycarcide noes bea ne ka Ben Paes Nematode disease, p. 56 4. Vegetative parts of the plant (roots, leaves or stem) GINS CRISES oA Pee ee IE eee en wee ee Ae eae 5 Hrntinespartior the: plant (the head) diseased- 4... 454044550440 08 21 5. Stem and leaves stunted, light colored or with light green streaks, maturing early or dying before TAOATUNENTNTS TOO OIWET TOWEL. co Gos oda bao os ochSeanceceusmenooe 6 Leaves or stems obviously diseased, bearing pustules, seloas: Gir Cligenlormach Sows oe do He cob ooo eSooosavoocebabesaccuc 8 6. Leaves mottled with alternating fine streaks of dark and yellow green, plants often dwarfed and roset- ECL, TROOUES) Hjojremaahy leeilyooccocosccoocucncubounce Mosaic, p. 52 Leaves lacking a mottled pattern, roots obviously CU SCASCO Petes ie 5 Seat car occ ER os cover sUlcke eiuaaceeD tee ens aE Pe Teen { 7. Roots covered with small, irregular, brown spots, or else the entire root decayed, brown and OVAL CIOs ON eee as So eye einen aes Helminthosporium disease, p. 33 Roots brown and dead by jointing time, those near the crown thicker than normal and woolly............ Take-all, p. 55 Sau Discase attack apparent chiefly on the stemis.>.:-..4-..+4---..+- 9 Disease attack apparent chiefly on the leaves.................... 15 9. Stems bearing red or black pustules or stripes.......... ....... 10 Stems affected with discolored spots or blotches................. 1G 10. Pustules reddish or black, with ragged edges....Black stem rust, p. 20 Stripes very long, at first lead colored, later rup- turing and emitting black powder................. Flag smut, p. 40 Bin Stems aiscoloredsat or near the: joints... -)-- sa see = series crises oe 12 Seem Seaiscolonredmel sew heneeamerciiars clei ere iete ete eels ane eer alicy 12. Discolorations sparingly dotted with black pustules. .Glume blotch, p. 47 Discolorations brownish and water soaked.........: Anthracnose, p. 31 13. Upper part of stem affected; water-soaked, black- [STOW MAUSAY OES [OREO ok gee odie peo acco nontaacoes Black chaff, p. 45 Basaltpantvor stemwmathectedn. Os. oa-c6 ecm (© ohne oe tere 14 16 14. 15. 16. ie 18. 119: 20. Ale 22. 23. 24. 26. ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 Stem base bearing numerous rust-brown spots or Streaks: .fis5,2 on nec ens eee ree Helminthosporium disease, p. 33 Stem base dark brown to black, usually a plate of fungous tissue between the stem and sheath......... Take-all, p. 55 Leaves with orange-red, open pustules or black, covered: pustules’s :tnc: o3¢\-[asid. Obs. o et ira ee ee Leaf rust, p. 17 Leaves showing symptoms other than pustules..................... 16 Leaves green throughout but wrinkled, twisted or OthernwiserdclobMnede pee erect eae Nematode disease, p. 56 Leaves discolored by spots, which are generally PLOWS cc6%G0 ais hs wie ngs ch Sere eased eee a ide Shee oe 17 Spots thinly covered by a superficial, powdery MOG ws he Pe ea ete ee ee cies Powdery mildew, p. 50 No moldon the outside on the leat... 2. ses 2 ie eee 18 Leaves bearing very long, lead-colored stripes which break open and discharge a black powder.......... Flag smut, p. 40 Spots on the leaves round to oval or elongated.................... 19 Leaf spots elongated, tan to reddish brown, studded with, black dOtsact eee omen: hte eae once Speckled leaf blotch, p. 25 Leaf spots round to oval, definitely brown bordered............... 20 Leaf spots dark brown, with a few black dots...... Glume blotch, p. 47 Leaf spots light or dark tan, without bIAekKdOtSi ce. sine do eo ere one Helminthosporium disease, p. 33 Chaff and grain entirely replaced by a mass of blacks powder selre:.5 ck s ecm cite © 2 oe eek rene ene Loose smut, p. 38 Chaff not replaced by black powder. .-........--.=- =. ses 22 Heads normal yor nearly.So,.in Colom sae a ee eee eee 23 At least the chaff showing definite discolorations................ 25 Kernels, when crushed, breaking up into a foul- sniellinesblackspowd cleric iene ee Stinking smut, p. 36 Kernels: «Solid):. 2s 8 sehe 2 cles con ens susie soho Biaye soe ee 24 Kernels expanded into long, hard, black bodies........... Ergot, p. 50 Kernels short and hard, the heads shorter, and stay- ing green longer, than normal.............. Nematode disease, p. 56 Part of the head, or all of it, blighted and ripening prematurely.<.... 5 cect. dew ce evi dees eww cs oes on 26 Head! ripenins, more or less normally.:>:-5----..-.--- eee PAE Affected parts of the head with very minute black dotsvonsthersurbace aye soc ee cmeke ciate eee nee Anthracnose, p. 31 Affected parts of the head clear or often covered by pink. MOLE <2 gen Word ces we Sr oeee 6 eee CATES one or etek eae Seab, p. 28 Chaff blackened, sometimes with beards twisted and blackened eve kon se aS cle cca ae ee Black chaff, p. 45 Chatt discoloredswath) blotchesy or! spotsee. aac oe eters eee 28 Dull water-soaked areas at the base of the chaff. . Basal glume rot, p. 43 Discolorations on the upper pau OL the Cath ee cece ere ener Chaff showing dark, sunken stripes on the upper [Of Hl a) Re nore teens Corals ue hemes Che, Ghia e coals ca Nine Cucina Black chaff, p. 45 Chafieshowanor denies poussins cic eiercieicrne cene ence acc neen eet 30 Spots irregular, brown with light centers containing a few: black dotss ... tee seiclsoe corinne sc cet Glume blotch, p. 47 Spots well defined, tan with brown 33 DOTGERSE Si hacst settee eae cree Ree Helminthosporium disease, p. BOEWE: DISEASES OF SMALL GRAIN CROPS 17 LEAF RUST Puceinia rubigo-vera, var. triticina Leaf rust, less commonly called orange leaf rust, attacks only wheat and, so far as is known, does not infect wild grasses. Like all rust diseases of cereals, it is capable of making use of an alternate host, but in America apparently does not do so com- Fig. 4.—Leaf rust of wheat. The dark spots scattered over the leaves, between the veins, are the rust pustules. These are orange red during the growing season and produce the rust spores by which the disease is spread. monly. Specialized forms, like those of stem rust (see page 20), show considerable selectivity with regard to the wheat varieties they attack, and over 40 such forms have been found to occur in the United States. Appearance.—As its name implies, leaf rust is found mainly on wheat leaves. Here it shows as small, round, raised, orange pustules the size of a pinhead or smaller, fig. 4. In the early part of the growing season these pustules are few in number and scattered irregularly over the leaf surface. Later in the season they become very abundant, and in years of heavy rust all the leaves appear plastered with them. Leaf rust pustules owe their color to the masses of summer spores they contain. 18 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 As wheat nears maturity, other pustules of about the same size, but dark in color and less ragged and powdery, appear in abun- dance, both on the leaves and on the sheaths; both types of pustules remain until the wheat plant has matured and died. Life History.—It has been proved experimentally that the wheat leaf rust fungus has an extended and complicated life history, like that described for stem rust, in which five distinct kinds of spores are produced and use is made of an alternate host that is neither one of the cereals nor a grass. The spores formed in the dark, closed pustules as the wheat plant ripens serve to carry the fungus over winter. In the spring these spores germinate, sending out short tubes bearing four short branches, on each of which a special spore is formed that is capable of in- fecting only herbs known as meadow rue, which botanists call Thalictrum. However, no instance of the natural occurrence of this rust on meadow rue has been found in Illinois. In experi- ments, minute spores have been produced on the upper surfaces of the swellings on artificially infected meadow rue leaves and cluster cups filled with spores on the lower surfaces. Spores from the cluster cups, if transferred to wheat, would produce infec- tion, followed first by orange pustules from which summer spores are shed and later by dark pustules containing winter spores. Native American meadow rue species have proved less suscepti- ble to leaf rust than foreign species. For practical purposes, the life history of wheat leaf rust in Illinois, as also throughout North America, may be considered as limited to the summer spore, or orange leaf rust, stage. The orange pustules produce spores in enormous numbers, and these are caught up on the wind and carried short or very long dis- tances. Undoubtedly the rust overwinters in its summer spore stage in southern states, perhaps even in Illinois, and in the spring is carried northward on the wind, producing new infection as soon as favorable weather occurs. Once established in a wheat field, it produces summer spores in such great abundance as to assure its spread throughout that field. Importance.—Taken year after year, leaf rust is the most serious disease attacking wheat in Illinois, outranking even speckled leaf spot in destructiveness. Estimates covering a con- tinuous 10-year period indicate an average reduction in yield of 4 per cent, equivalent to approximately 1,370,000 bushels annually. Losses have ranged from as little as a trace, in 1928, to as high as 12.5 per cent, in 1935, and during the period 1926 to BOEWE: DISEASES OF SMALL GRAIN CROPS 19 1935 have amounted, in total, to 53 per cent of all wheat losses attributed to disease attack. The destructiveness of leaf rust is due to its effect upon leaf tissues. Light rust attacks which occupy only small amounts ~ fo) e) Oy) (e) IN LJ O < Kk Zz LJ O ad WW Oo < LJ a cent metallic copper) is used at the rate of 242 to 3 ounces per BOEWE: DISEASES OF SMALL GRAIN CROPS 12: Ww bushel. Copper carbonate especially prepared for seed treatment should be used. The finer it is ground the better disinfectant it is. The size of the dust particles is almost as important as the copper content of the chemical. To be effective, the dust must be Fig. 46.—Oil drum mixer, for treating seed grain with copper carbonate and other dusts. (Photograph furnished by the author.) fine enough to pass through a 200-mesh screen, but dust fine enough to pass through a 300-mesh screen is better. A mechanical mixing machine must be used for copper car- bonate, since each kernel must be coated thoroughly. The shovel method of mixing is not efficient enough for this dust. An oil drum, a commercial treating machine or a concrete mixer can be used. Formaldehyde Treatments.—Formaldehyde, a gaseous dis- infectant, has been used since 1897 for seed-borne diseases. It has proved especially effective in controlling the oats smuts. It is not effective, however, in controlling such diseases as barley stripe and loose smut of wheat. For seed treatment, formaldehyde is now available as forma- lin, which is a liquid containing from 37 to 40 per cent of dissolved formaldehyde gas, and also as formaldehyde dusts. These dusts, 124 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 which are sold under proprietary names, contain from 4 to 8 per cent of formaldehyde gas adsorbed on the surface of the dust particles. Formaldehyde has certain disadvantages. It irritates the mucous membranes of the operator. It may injure the seed, if it is used carelessly; and, because it leaves no coating on the seed, it does not give lasting protection against infection. It evaporates quickly, and treating solutions must therefore be used imme- diately after being prepared if they are to be effective. Formaldehyde injury to seed results mainly from the pene- tration of the gas through the seed coat and into the germ. Such injury is especially apt to occur when treated seed is dried without being aerated. It can also occur as a result of absorption of the disinfectant by cracked kernels and even by sound kernels through broken seed coats. The lack of aeration that attends the sowing of treated seed in dry soil can result in severe seed injury; hence, it is advisable to keep treated seed moist until it is sown and to sow it in moderately moist soil. Four methods of application are commonly used in treating cereal seed with formaldehyde: the spray, the sprinkle, the dip © and the dust. The choice of method is governed chiefly by the kind of seed to be treated. The spray method is adapted only for the treatment of oats seed. The sprinkle and the dip methods can be used with all other kinds of cereal seed. Formaldehyde dusts can be used with all kinds of cereal seed for diseases suscep- tible to formaldehyde treatment. The spray method, known as the “dry”’ formaldehyde method before the invention of the dust method, is the procedure most often used today. In this method, a solution consisting of 1 pint of full strength formalin and 1 pint of water is required for each 50 bushels of seed to be treated. An ordinary fly-poison sprayer that throws a fine mist is satisfactory for applying the solution. The cleaned seed is placed in a pile on the granary floor, a wagon bed or a canvas. As one man shovels the seed from this pile to another, a second man sprays the solution uniformly over the seed. Usually two strokes of the sprayer plunger are sufficient for each shovelful of grain. The pile of sprayed seed should be covered with canvas, blankets or sacks which also have been thoroughly sprayed with the same solution. It should be kept covered for at least 5 hours and may be left covered overnight. The seed can be sown immediately after treatment has been completed. BOEWE: DISEASES OF SMALL GRAIN CROPS 125 Seed can be treated by the spray method at any time prior to sowing if, after being treated, it is thoroughly aired before being bagged for storage. The bags used should be treated with the formalin solution to prevent recontamination of the seed. In the sprinkle method of formaldehyde application, the solu- tion usually recommended requires 1 pint of full strength formalin in 40 gallons of water for each 50 bushels of seed. The temperature of the water should be between 60 and 70 degrees F. An ordinary garden sprinkling can is satisfactory for applying the solution. The cleaned seed, spread out thinly and evenly on a smooth sur- face, should be sprinkled with the solution and then mixed by being shoveled until each grain has been thoroughly wet with the solution. The seed should then be shoveled into a pile, and the pile should be covered with canvas, blankets or sacks soaked in the same solution. The pile should be kept covered for at least 2 hours and may be left covered overnight. Seed treated by the sprinkle method should be sown imme- diately after completion of the treatment, in a moderately moist soil. The rate of seeding must be adjusted on the drill to allow for the seed swelling that has occurred. In a modification of the sprinkle method, a solution containing 1 pint of formalin in 10 gallons of water is required for each 80 bushels of seed to be treated. This solution is applied with a sprinkling can, as directed above, at the rate of 1 pint per bushel of seed. The seed is then mixed thoroughly, piled and covered as previously directed. The pile should be kept covered for 3 hours, after which the seed should immediately be sown or spread out in a thin layer to dry. If the seed is dried before being sown, occasional stirring of the seed as it dries will hasten escape of the gas and reduce the chance of injury. The dip method of applying formaldehyde is the most de- pendable for the reason that, if carried out thoroughly, it insures the disinfection of every kernel. The solution required in this method consists of 1 pint of formalin in 40 gallons of water. The temperature of the water should be between 60 and 70 degrees F. The treating solution may be placed in a tank, a barrel or any other suitable container. The seed to be treated, after having been cleaned, should be placed in loosely woven burlap bags— the bags should be not more than half filled—and agitated in the solution until every grain is wet. The seed should then be drained, emptied from the bags and allowed to dry for at least 2 hours. It should be sown immediately in a moderately moist soil. If it 126 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 cannot be sown within about 12 hours after being treated, it should be spread out thinly to dry and should be stirred occasion- ally to hasten escape of the gas and prevent injury. Wheat Seed, because it is more susceptible to formaldehyde injury than oats seed, should be presoaked prior to treatment by the dip method. Each half bushel of cleaned seed, in a loosely woven sack, is soaked in water for 10 minutes, drained and set aside for about 6 hours. Then it is immersed and agitated in the treating solution for 10 minutes, removed, drained and set aside in the sack for another 6 hours. After this time, it should be emptied from the sack and spread out thinly to dry overnight. If seed is presoaked early in the morning, it can be treated at noon, spread out to dry in the evening and sown the following day. With this treatment, an adjustment of the drill must be made, increasing the indicated rate of seeding about 25 per cent, to compensate for the swelling of the seed. Formaldehyde dust, like any of the other antiseptic dusts, can be applied to grain seed with a mixing machine or a gravity mixer. It has the advantage of being easier to apply than liquid formaldehyde. It gives off formaldehyde gas slowly and is there- ° fore less apt to injure the seed than are the formaldehyde solu- tions. In using a formaldehyde dust, the grower should adhere strictly to the rate of application of the dust and all other instruc- tions given on the package or in directions furnished by the manufacturer. Hot Water Treatments.—Although the hot water seed treat- ment kills both external and internal seed infection, it is not recommended for general use because the average farm lacks facilities for performing the treatment satisfactorily. It is rec- ommended, however, to producers of certified seed. If use of this treatment can be made a community project, every farmer in the community can have treated seed for his fields or at least enough treated seed to plant a seed plot from which disease-free seed can be obtained later. Local creameries often offer good facilities for treating seed by this method. The treatment may be used wherever the necessary tanks or vats can be assembled, if a boiler is available to furnish steam for heating the water used in the tanks. Since the effectiveness of the hot water treatment depends upon raising the temperature of the seed high enough to kill any internal infection but not quite high enough to kill the seed germ, many of the weak and cracked seeds. and those with broken seed BOEWE: DISEASES OF SMALL GRAIN CROPS 127 coats will be killed by the treatment. It is, therefore, necessary to test the seed for germination after it has been treated and in- crease the rate of seeding to compensate for the seed that has been killed. There are two forms of hot water seed treatment, the long- soak or single-bath method and the modified or short method. The latter is the one generally used. Necessary equipment for either treatment includes a standardized, accurately graduated thermometer, a source of live steam to maintain water tempera- ture and tanks large enough to accommodate the amount of seed to be treated. In hot water treatment by the modified method, three tanks are necessary. Each tank is partly filled with water. The water in one tank is not heated, that in the second tank is maintained at 120 degrees F., and that in the third at 129 degrees F. for wheat and rye and 127 degrees F. for barley. The temperature in the second and third tanks must be kept as nearly constant as possible by live steam which is led into the tanks through hose or pipes and allowed to bubble up through the water. Thoroughly cleaned seed, sacked in half-bushel lots in loosely woven 2-bushel sacks, is soaked in the cold water tank 4 to 5 hours, removed and allowed to drain. Next the seed is submerged and agitated in the second tank (120 degrees F.) 1 to 2 minutes to raise the temperature of the seed nearly to that of the third tank. The seed is then quickly transferred to the third tank and agitated in the water. If the temperature of the third tank has been maintained exactly as directed, the seed must be removed from the tank at the end of 10 minutes and cooled. Treated seed can be dipped in cold water, or emptied from the bags at once, spread out in a thin layer and stirred occasionally. The seed must, of course, be dried as soon as possible. If the treatment is to be effective the temperature of the water in the third tank must not be allowed to fall below 124 degrees F. for wheat seed, or 125 degrees for barley seed. And it must not be allowed to rise above 131 degrees when treating wheat seed or above 129 degrees when treating barley seed, for temperatures higher than these will kill the seed. If the tempera- ture varies from that recommended, it is necessary to vary the treating time accordingly. In the treatment of wheat, for ex- ample, if the temperature falls to 126 degrees, the seed should be soaked 15 minutes, but if it rises to 130 degrees the seed should be soaked only 8 minutes. Soaking the seed for periods longer 128 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 than those recommended is certain to result in serious seed in- jury; soaking for shorter periods reduces the degree of disease control obtained. For the long-soak hot water treatment, only one tank is needed. The seed, sacked as directed for the short method, is immersed in hot water in the tank without having first been soaked in cold water. The temperature of the water may be main- tained at either 120 degrees or 118.5 degrees F. At 120 degrees the seed should be soaked 1 hour and 35 minutes; at 118.5 degrees it should be soaked 1 hour and 50 minutes. When the treatment has been completed, the seed should be removed from the tank, emptied from the sacks, spread out thinly and stirred occasion- ally so that it will dry quickly. Organic Mercury Treatments.—Certain organic mercury compounds, because of their high antiseptic value, are especially well adapted to the control of fungous and bacterial diseases of plants. For the control of cereal diseases, one of the most useful of these compounds, available as New Improved Ceresan, is pre- pared as a dust, the active ingredient of which is ethyl-mercury- phosphate. This chemical not only gives off an antiseptic gas which is immediately effective but also leaves on the seed an anti- septic coating which protects seed from decay and seedlings from blight. It can be used on all kinds of cereals and controls all seed- borne diseases except the loose smut of wheat. It gives excep- tionally good control of barley stripe. Although organic mercury dusts can cause seed injury if they are improperly used, they possess a number of advantages over the older materials. They cause no swelling of the seed, such as occurs with liquid treatments, and adjustment of the seeding rate on the drill is therefore seldom necessary. Because they are used in smaller amounts, they make less dust in the air to be inhaled by the operator while treating seed and handling it later. They do not interfere with the flow of seed through the drill, clog the drill or cause excessive wear of its parts. They can be applied to the seed of all the small grains with the same type of mixer. Organic mercury dusts are poisonous. Seed treated with such dusts should never be used as human food or as feed for livestock. Treatment of seed should be done in the open or in a drafty place, so that the operator will not be compelled to inhale much of the dust. If possible the operator should wear a dust mask. Mercury dusts should be applied at the rate recommended by the manufacturer. The ethyl-mercury-phosphate dust which BOEWE: DISEASES OF SMALL GRAIN CROPS 129 contains 5 per cent of that chemical is used at the rate of one- half ounce per bushel of seed. The dust should be applied to the seed with one of the mixing machines previously described, a gravity mixer or a commercial seed treating machine. If it is seep TREATER * @ 6 : ‘ wip Beg Pot Pay 4 iil hitl ane if Fig. 47.—Minnesota gravity mixer, for treating seed grain with mercury dusts. (Photograph furnished by M. B. Moore, Minnesota Agricultural Experi- ment Station.) 130 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 35 impossible to apply the dust in any of these contrivances, the application can be made by hand, as follows: Spread a bushel of seed thinly on a flat, smooth surface and sprinkle evenly over it the required one-half ounce of dust; spread a second bushel of seed on top of the first and add the dust; repeat the process until all of the seed has been placed in the pile. Then shovel the entire pile over three or four times to mix seed and dust thoroughly. Let the pile stand for 24 hours before sowing the seed. A dust mask should always be worn by an operator using the hand mix method. Some variations are necessary in handling the treated seed of different cereals to secure best results from the organic mer- cury dust treatment. Wheat seed should be treated at least 24 hours before it is to be sown and should be kept in a covered pile or in bags during that time so that the gas given off by the dust will be effective in killing surface-borne infection. It should not, however, be kept longer than two months before being planted. Barley seed should be treated at least 24 hours, prefer- ably 72 hours, before being planted and should be kept in a cov- ered pile or in bags during the intervening time. It can, however, - be treated as long as six or eight weeks before planting time. The injurious effects resulting from the storing of seed treated with organic mercury dusts can be prevented if the quantity of dust used per bushel is reduced in accordance with the length of time the seed is to be stored. For example, if seed is not to be sown for t be pigcatment but is to be sown within a week, three-ei Ss ounce, instead of one-half ounce, of dust is sufficient for the)treafhinDdSeach bushel, and if seeding is to be delayed for A yhiPERETTY OF ALLENOIBOne-fourth ounce of dust per bushel is sufficient. Although liquid treatment with organic mercury compounds is widely used in plant disease control, it has little value in the control of cereal diseases, except as a supplement to the hot water treatment. For this purpose hydroxymercurichlorophenol, avail- able as Semesan, is prepared according to the direction of the manufacturer (1 ounce of chemical in 3 gallons of water) as a 1 to 400 solution in cold water. Seed, after being removed from the hot water bath, is immersed in the cold organic mercury solution, which both cools the seed and aids in the control of sur- face-borne infections. The liquid organic mercury treatment also stimulates germination of the treated seed and thus compensates for the injury done by the hot water treatment. ey ~~. “UU 3 0112 01754118