-—o—

ey

Vv

CIRCULAR No. 70.

United States Department of Agriculture,

BUREAU OF ENTOMOLOGY,
L. O. HOWARD, Entomologist and Chief of Bureau.

THE HESSIAN FLY.
( Mayetiola [Cecidomyia] destructor Say.)

By F. M. Wesster,

In Charge of Cereal and Forage-plant Insect Investigations.

Probably no other insect causes more damage to the wheat crop
of the United States
than the Hessian fly,
though the chinch bug
is doubtless a close
second. During years
when it is excessively
abundant, hundreds
of thousands of acres
of wheat may be either
totally destroyed or so
badly injured as to re-
duce the yield 50 to 75
per cent, and the mon-
etary losses expressed
in dollars would run
far up into the mil-
lions. This insect isan
old depredator, in the
sense that it has long
been known to ravage

our wheat fields, yet
farmers are, in many cases, still at a loss regarding the best methods
ot warding off its devastation.

Figc.1.—The Hessian fly ( Wayetiola destructor): Adult female, much
enlarged (original).

EARLY HISTORY IN AMERICA.

The common name, ** Hessian fly,” was long ago bestowed upon this
insect by Americans, because of its having committed some depreda-
tions on Long Island, New York, in 1779, in the vicinity of Lord
Howe’s old encampment of three years before. The Hessian merce-

(1)

9

naries who constituted a part of this army were much despised, both
at home and in America, and, on the supposition that these soldiers
had brought the pest
\ with them from their
native country in the
straw used for their
bedding while en route,
it was given the obnox-
ious name of ** Hessian
fly.” Whether or not
this theory of its in-
troduction was well
founded can never be
either substantiated or
disproven, and all that
‘an now be said is, that
the pest was imported,
probably from some
trans-Atlantic country
\ and some time during
/ \ the latter half of the
Fic. 2.—The Hessian fly: Adult male, much enlarged (from eighteenth century. As
cerita a matter of interest, it
may be stated that, in some quarters, the more ignorant Tory element
of those days claimed that General Washington was responsible for

this pest. It was not technically described until 1817.

DESCRIPTION OF THE INSECT.

The fly itself (tig. 1, female; fig. 2, male) is very small, being only
about one-tenth of an inch long, the body of an
obscure dark color, and the form much like that |
of a very small mosquito. The abdomen of the i
female (fig. 1) is red, or yellowish when first

—<—<———__

|
1
hatched from the ‘‘ flaxseed,” the color varying
with age, the posterior segments terminating in
a compressed cylindrical, very minutely hairy ,
ovipositor, capable of great extension. The male
(fig. 2) is smaller, more slender, and in color gen- dT |
erally darker than the female, the abdomen ter- | |
minating in asomewhat intricate organ composed
of a set each of outer and inner claspers. |
The egg (fig. 3) is very minute, being only | ||
about one-fiftieth of an inch in length,cylindrical, Fie. 3.—Egg of Hessian fly,
roundingly pointed at the ends, glossy translu- Hieneiantreg es rity nce
cent, and slightly reddish, this color deepening _ ingeggsasusuallydeposited,
with development. ear ease a
The larva or maggot (tig. 4), when newly hatched, is a little smaller

than the ege, with a slightly reddish tinge; later, as it increases in

size, it is at first white and afterwards ereenish white, clouded inter-
nally by flaky white.

The flaxseed (tig. 6).—This is the name given to the insect after the
larva has reached its full growth and the skin has hardened and turned
brown, forming a covering known as a puparium. There
is at this time a minute, brown, forked process on the
underside of the anterior end of the larva, known as the
** breastbone” (fig. 5), the use of which is not fully under-
stood. It is not present, however, until the larva enters

the flaxseed state. Within this ‘* flaxseed”
7; it transforms first to a pupa(fig. 7), and from
this to an adult fly. The term ‘‘ flaxseed”
is applied partly because of its brown color

and partly because it is more or less flat- eas i
C ae iq, 4.—The
tened, thus giving it somewhat the appear- Hessian ay:
ance of a flaxseed. LA ee)
fore ‘‘ flax-
Sieied77 suas
WHERE TO FIND THE DIFFERENT STAGES. formed,
much = en-
From the foregoing descriptions it will — lerged (rig:

"3 a a 2 inal).
FIc.5.—TheHessian De Observed that, during the life of this

fly: Larva taken jnsect, it is found in four very different forms, so

from ‘‘ flaxseed,” : . : F
much enlarged, entirely unlike in appearance as to confuse the average

with “breast- stat
bone” still more AL ATIGIE. . |
enlarged‘at right rhe eggs (fig. 3), which may be easily seen by one
(original). = - j A ;

with fairly good eyesight, are generally placed in the
grooves of the upper surface of the leaves, though they -are occa-
sionally found on the underside of the leaf. When the
young wheat plant is just pushing through the ground,
the egg is sometimes placed on the outside,
because no leaves are available. The young
larva is slightly smaller than the egg, and
as soon as it is hatched it makes its way
down the leaf and behind the sheath. In case
of young wheat it descends to just above the
root, but after the plants have begun to joint it
can go no farther than the base of the sheath Fic. 6 —The
belonging to that particular leaf, which is al- ae
ways at the joint. Where excessively abun- or ‘‘flax-
dant, the larvee will frequently be found on the ee aioe
Fic. 7—The Hes- ]ower stem ranged one behind the other, the (omsime).
sian fly: Pupa 6 2 : G
taken from anterior end of one pushed slightly under the posterior
tora as end of the one in advance. Very often this position is
larged (after maintained throughout the entire development of the
ene ee larva (figs. 4 and 5), and the flaxseeds (figs. 6 and 10)
still retain the same relative position. The fall brood of larve and
the overwintering flaxseeds are to be found just above the roots (tig. 10),

f=)

+

except in cases where the young plant has become disintegrated and
separated at the point of attack in the fall or the plants have been
heaved out by the action of freezing and thawing, in which case they
may be scattered about on the surface of the ground.

The young make their way down the plant head foremost, and so
remain until before pupating, when they reverse their position in the
flaxseed and are then situated head upward, and thus pass into the
pupal stage. Before the fly issues, however, if the flaxseed is not
situated conveniently for its escape, the pupa will push itself, if pos-
sible, to such a point, and frequently empty pupa skins may be
observed protruding from under the sheaths of the leaves.

The fly itself is not easily observed until one becomes familiar with
its appearance, and this will account for the great variety of insects
that are continually mistaken by farmers for the Hessian fly. Much
of this difficulty may be obviated if farmers will look for an insect
like that shown in figure 1, but very minute and somewhat resembling
a very small mosquito. During warm days, in the egg-laying season,
the flies may be observed flying about in the young wheat, alighting
upon the leaves. In cooler days, or in early morning while a heavy
dew is on, they will be down among the leaves, or even on the ground.

LIFE HISTORY.

At present all indications point to the probability of tne Hessian fly
being two-brooded, at least during favorable seasors, over its entire
area of distribution in the United States.

In the South the two broods are the most widely separated, while
in the North, in the regions of spring-wheat growing, they seem to
follow each other in quick succession.

LIFE HISTORY IN REGIONS OF FALL-WHEAT GROWING.

Throughout the fall-wheat-growing sections the fly passes the winter
in the young wheat, mostly in the flaxseed stage, but also to some
extent as from two-thirds to full-grown larva. It is difficult to esti-
mate the number of these larvee that will winter over and remain alive
until spring, owing to the fact that it is impossible to determine whether
they are alive or dead until they begin to decay. But where we have
attempted to rear them, even though apparently alive, comparatively
few adults have been obtained, though of course this mortality would
probably vary somewhat with the severity of the weather during
winter.

In spring (from March, in Georgia and South Carolina, to May, in
Michigan) the flies escape from the flaxseeds and deposit their eggs on
the wheat, and the young from these develop to flaxseeds before har-
vest, passing the summer in the stubble. The flies from overwintering
larvee come on later; and it is quite probable, also, that Some of the
very earliest deposited eggs may give rise to adults at about this

oD

5

time; thus, owing to this overlapping, during some seasons and in
some localities, there appears just before harvest what has by some
been considered a supplementary second brood.

In autumn the time of appearance of adults as between North and
South is reversed. In northern Michigan the adults of the fall brood
are abroad, under normal meteorological conditions, during the last
days of August and first days of September. In Georgia and South
Carolina, under the same conditions, it may be the last of Novem-
ber or the first of December before they have all left the stub-
ble. Thus has the species adapted itself to the prolonged southern
summer, during which there is little or no food ‘for the larve. While
there are stragglers, the major part of the brood will appear and dis-
appear within the space of a few days, probably within a week, and
the flies, by preference, will deposit their eggs on the younger plants,
those of one or two leaves seeming to suit them best. At this time
the young Jarve make their way downward nearly or quite to the roots
(fig. 10). The normal outcome of this brood is that the individuals
reach their development as larvee, pass into the flaxseed stage, and pass
the winter as such on the young wheat plants. But here again the
earliest deposited eggs may produce adults before the winter sets in,
and the delayed individuals occurring at this time may unite and
another supplementary brood, as it has been termed, may be produced.
The economic significance of this so-called brood depends much on the
weather, as, if winter sets in before the larve have sufficiently matured
to withstand its rigors, these must necessarily perish, while, if the
mild autumn weather is greatly prolonged, more or less of them may
winter over uninjured.

LIFE HISTORY IN SPRING-WHEAT REGIONS OF THE NORTHWEST.

The statements here made are based largely on the careful investi-
gations carried out by Mr. George I. Reeves, a special field agent of
this Bureau, during the season of 1905. This single season may have
been an exceptional one, in that the spring was backward, the summer
wet, and the mild autumn weather continued later than usual. The
results must not, therefore, be taken as wholly conclusive.

In North Dakota the insect winters in the flaxseed stage in both
stubble and volunteer wheat. chiefly the former. Egg laying begins
late in May, and during seasons with plenty of rain the second brood
follows the first in quick succession, being reenforced by the con-
tinued emergence of flies from stubble of the previous year. Here
the summer conditions are different from those in the East and South,
and the breeding season extends from about May 20 to October 1, or
throughout the entire summer. In other respects the habits of the
insect do not seem to differ from what they are in the fa!l-wheat-
growing section of the country.

6

DISTRIBUTION.

Outside of America the Hessian fly occurs in North Africa, western
Asia, Europe, British Islands, and New Zealand. In the Dominion of
Canada Doctor Fletcher has found it from Prince Edward Island to
Indian Head, Saskatchewan. On the Pacific coast it probably occurs
from southern California to British Columbia; but as no exact investi-
gations have been made there, this statement is to be considered as
only approximately correct.

Our previous notions of the distribution of this insect over the
country east of the Rocky Mountains will have to be revised. The
accompanying map (fig. 8) will show the extent to which this revision
becomes necessary. The original of this map appears in Bulletin 16,

Fig. 8.—Map showing distribution of the Hessian fly in America (altered from Osborn).

new series, of this Bureau (issued in 1899). The heavy broken line
indicates the present western and southern limits of Hessian fly dis-
tribution based on our latest observations and data furnished by Pro-
fessor Bruner, of Nebraska, and Mr. R. I. Smith, entomologist of the
Georgia State crop pest commission. This is believed to be approxi-
mately correct. It also seems to show that the insect must have been
first introduced into the Pacific coast region in or with articles of
inland commerce, and (unless it be found to infest native grasses) that
it did not reach there by natural diffusion, a point that has not before
been definitely stated so as to be clearly understood.

Experimental sowings of wheat near Sault Ste. Marie, Mich., dur-
ing the last two years do not reveal its presence there, and no attempt

7

has been made to study its occurrence in the spring-wheat-growing
sections of Maine. While its absence in some parts of the country
between the Platte River, in Nebraska, and the Canadian boundary
line might be attributed to a lack of its food plant, this will not hold
in southwestern Kansas and Oklahoma, as in those localities it seems
to suddenly terminate in the midst of a wheat-growing section, and
where this grain has been cultivated for at least twenty years. Strange
as this may at first appear, Doctor Merriam, of the Biological Survey,
informs the writer that he finds several parallel cases in the distribu-
tion of some of the smaller mammals.

FOOD PLANTS.

While the female fly will often deposit her eggs on grass, or even
weeds, the larvae, so far as known, survive only on wheat, barley, and
rye, proportionately in the order mentioned. From time to time
** flaxseeds” closely resembling those of this insect have been observed
on the stems of several native grasses, but adults reared from them
have not been considered as belonging to this species, owing to sup-

bo) bo) c=)
posed structural differences, and no experiments have been made to
ascertain whether or not it is possible for larvee of the Hessian fly to sur-
vive on these grasses. Doctor Forbes some years ago failed to induce
the insect to breed in either redtop, bluegrass, foxtail, or orchard
grass—species on which ** flaxseeds” had, however, not been found.

Flaxseeds resembling those of Hessian fly have been found on Ely-

fo) . PY,
mus, Agrostis, Bromus, and Agropyron, in California, by Mr. Koe-
bele, and on the latter also in Indiana, by Mr. W. J. Phillips, a field
agent of this Bureau. Besides, Doctor Lindeman found similar flax-
seeds on timothy and Agropyron repens in Russia.

EFFECT OF LARVZ ON THE PLANT.

The effect of the larvee on a young wheat plant is very marked and
becomes observable soon after the young reach the stem under the
sheath. Once he has observed it, any farmer can readily detect an
infested plant, or a single infested tiller may be as readily detected in
a cluster without taking the trouble to remove the plant from the
ground.

For the purpose of comparison, illustrations are given of an unin-
fested young plant (fig. 9) and an infested young plant (fig. 10). An
uninfested plant is of a more slender growth, the green color is lighter,
with a slight tinge of yellow, the stems are more or less visible, and
the central unfolding leaf is present. The whole plant is inclined to
droop and the tillers spread out and cover the ground. An infested
plant is without stem and the leaves are broader, usually shorter and
of a deep bluish-green color, somewhat resembling those of oats. The

8

plant stands more erect, and, in fact, is but a mass of short overgrown
leaves that usually kill with the first frost. Figure 10 shows a young
tiller starting out from below the part attacked by the fly. If this
tiller were to be attacked after it appeared above ground, there would
follow the same appearance as in case of the original plant; that is to

Fig. 9.—Healthy young wheat plant (original).

say, the leaves would become broader and of a darker color. The
foregoing statement will apply to a severe attack on fall wheat in
spring and on young spring wheat. The only exception in the appear-
ance of infested young plants is in the case of the hard wheats, whose
foliage is broader and of a darker color, but the erect position will

9

still enable the observer to detect the infestation. Of course later on
the infested plants change to yellow and then brown, but the darker
color and rank growth of leaf always precede this.

In summer, in both spring and fall wheat, the effect of the fly is to

Fic. 10.—Young wheat plant infested by the Hessian fly (original).

cause the straw to break over before harvest. It is then said to be
** straw fallen.”

IMMUNE OR DISTASTEFUL VARIETIES OF WHEATS.
There is no such thing as *‘ fly-proof wheat.” Most wheats will suf-

fer when the plants are young, regardless of variety. In experimen-
tal sowings a variety that seems to escape attack one year may sufter

10

the next; and, while the insect may prefer certain varieties over others,
this all comes to naught in years of serious ravages or where the sup-
posed distasteful variety is in a condition more satisfactory to the
insect at the time of oviposition. It is doubtful, however, if this can
be said of the attack of the second brood on the more matured plants,
as it is quite noticeable that the ranker-growing varieties with strong,
stiff straw are the least affected. Then, too, among fall wheats in the
northern part of the country it is quite essential that a wheat plant
be able to send out tillers from the old roots of plants killed by the fly
(fig. 10), and that these tillers prove hardy enough to withstand the
winter. Therefore, in selecting varieties of wheat with a view to evad-
ing Hessian-fly attack, the farmer will do well to ignore statements on
this point from those who have seed to sell and select from the varie-
ties known to do well in his locality such as are of strong, vigorous
growth, hardy, and with a stiff straw. For some reason the durum or
macaroni wheats do not seem to attract the fly, at least not the second
brood. In going over fields of this kind of wheat in sections where
other spring wheats were suffering from attack by this pest, it was
rarely found on a stem of macaroni wheat, while any straws of other
varieties growing from seed that had become intermixed were almost
invariably infested. Whether this wiil hold good in case of the young
plants it is as yet impossible to say, because of the difficulty of telling
to what varieties the young plants belong. Infested plants have been
found in fields of young macaroni wheat in some considerable numbers;
but these plants may have been of other varieties, as the fields had been
used for other varieties the vear before, and besides the seed itself may
have been impure.
METEOROLOGICAL EFFECTS.

All who have carefully studied the Hessian fly, under various field
conditions during a series of years, have noted that weather conditions
have an important influence on the insect. Especially is this true in
its economic relations to the grains it attacks; hence, in the applica-
tion of preventive measures, these weather conditions become of vital
importance.

Many farmers place much stress on the effect of cold weather or
even of frosts in terminating the flies’ work in the fall, and it is for
this reason that many try to delay wheat sowing until after there has
been a sharp frost. The facts are that the females will be abroad and
ovipositing in freezing weather, and Mr. W. J. Phillips has found
by experimentation that the eggs will remain in a temperature of 36°
F. for seventy-two hours with no other effect than to delay their
hatching that much longer. This is about the temperature at which

11

frosts would occur. Indeed, the writer has observed eggs hatching
during the day in the fields when there were frosts nearly every night.
Whether or not the larvee from these would get sufliciently advanced
to pass the winter would, of course, depend upon later weather condi-
tions. In the North these much-belated larve are killed off by cold
weather.

The immunity of the late-sown wheat from attack by the fly is not
due to frost, but to the fact that, by the time severe frosts usually
occur, most of the flies have appeared and gone.

The most marked influence of climatic conditions on this insect is
seen in the effect of heat and drought, and especially of the two com-
bined. In the South it is the long summer that so widely separates
the two broods. Drought has a similar effect on the development of
the insect as it has on the germination of the seed which produces its
food; thus, dry weather in the late summer and fall tends to keep the
insect in the flaxseed stage—a fact of special importance in the North,
where it is imperative to get the wheat sown early enough to enable
the plants to stand the winter. Under exceptional conditions, such as
in a dry room, flaxseeds may be kept for a year, or even two, but
when moistened the flies will soon after emerge. So in the fields they
will, during a drought, remain in the flaxseed state for a considerable
time after they would appear under normal conditions, and only appear
soon after rains have moistened the soil.

NATURAL ENEMIES.

There can be no doubt that parasites play a most conspicuous part
in the natural control of the Hessian fly, and if we only knew the whole
truth of the matter we should find that these minute friends of the
farmer are worth many times their weight in gold. Not infrequently
one species of these parasites will overcome the pest in a neighbor-
hood so effectively as almost to exterminate it. Several times the
writer has found, in attempting to breed Hessian fly from young wheat
plants that had been killed by the larvee, that hundreds of these para-
sites would emerge from the flaxseeds, while only an occasional fly
could be obtained. Nearly all of these deposit their eggs in the bodies
of the maggots, but the fully developed parasites emerge from the
flaxseeds.

Professor Osborn “ has enumerated six species of these parasites, not
including the English species Entedon epigonus Walker. Polygnotus
minutus Lindm., which occurs in Russia, France, and England, is in

41898: Bul. 16, n. s., Div. Ent., U. S. Dept. Agric., pp. 28-29.

12

America represented by Polygnotus hiemalis Forbes (fig. 11), per-

haps the most useful of any in this country.

ULL

Fig. 11.—Polygnotus hiemalis, much enlarged (original).

It is very minute, and
Mr. Reeves has count-
ed over forty of the
larve within a single
flaxseed. It is black,
with yellow feet, and

the legs are dark
brown, banded with
yellow. The writer

has again and again
reared this in great
numbers from fall
wheat infested by the
fly and witnessed the
sudden check
tained by the pest the
following spring. It

sus-

is owing to this more than to any other influence that the Hessian fly

is now being held in check in the
spring wheat regions of the North-
west. Perhaps the next most useful
parasite is Hupelmus allynii French
(figs. 12, male, and 13, female). This
is generally distributed over the
country and affects both the Hessian
fly and the joint-worm. It is larger
than the preceding; the body is black,
with a greenish luster, and the legs
are more or less yellow. Jerisus
destructor Say (fig. 14) oecurs in
Europe, England, and America, but
not in such profusion with us as to

Fie. 12.—Eupelmus allyniu: Male, much en-
larged (from Riley).

afford the same relief to the farmer as in the case of the two preceding.

ee

Sf

Fig. 13.—Eupelmus allynii: Female, much enlarged

(from Riley).

in some individuals, while others are fully winged.

It also is black, but with a bluish
ereen metallic reflection, and the
legs are black, banded with yel-
low. MPlatygaster herrickiz Pack.
(fig. 15) is very minute, shining
black in color, and is supposed
by many to attack the egg of the
fly, but there is still some doubt
regarding this. Baotomus sub-
apterus Riley (fig. 16), as the
name implies, has aborted wings

The head and

thorax are of a dark greenish metallic luster, and the legs honey-

13

yellow. It is generally less abundant than some of the others, but
sometimes individuals are quite numerous. Besides these, several
undescribed species have been
recorded from the northwestern
part of the country. The influ-
ence of these minute parasites in
regulating the world’s wheat sup-
ply is not at all understood, and it
is doubtful if wheat could be sue-
cessfully raised were they all to be
suddenly swept out of existence.

REMEDIAL AND PREVENTIVE
MEASURES. Fic. 14.—WMerisus destructor, much enlarged (from
Of remedies there is little to be Riley).

said, since after the pest becomes established in a field it can not be
Be ee tee reached by any measure likely
gf: to destroy it. The application
broadcast of some quick-acting
fertilizer containing a_ large
percentage of phosphate, made
as soon as general infestation
is apparent (see fig. 10), will
cause the plants to tiller more
freely and give them sufficient
vigor to withstand the winter,
and thus increase the number
Fig. 15.—Platygaster herrickii, much enlarged (from Of healthy stems the following
a spring. Any other means that
could be employed having a similar effect would be a remedial measure.
All practical measures must necessarily be
in the nature of preventives, looking (1) to the
elimination of the pest in the young wheat in
the fall, and (2) to the increasing of the vigor
of the young plants in order to enable them
to counteract the insect’s effect, when present.
Under the first come late sowing, rotation of
_ crops, burning of the old stubble, and the de-
struction of volunteer wheat. Under the sec-
ond should be classed the enrichment of the
soil, its thorough preparation, and selecting

and properly sowing the best seed.

LATE SOWING.

By late sowing as here recommended is meant
moderately late sowing of fall wheat in any
locality, for extremely late sowing, which has
sometimes been advised, would be even worse than early sowing. The
later appearance of the fly in the fall, as we pass from the north south-

Fie. 16.—Baevtomus subapterus,
much enlarged (from Riley).

14

ward, has already been explained. At present the Bureau of Ento-
mology is conducting experiments in fall wheat sowing in nine States,
covering approximately the country between latitude 83° and 46>.
Here wheat is being sown every ten days during September, Octo-
ber, and November, year after year, with the expectation of determin-
ing the approximate date of safety for seeding in the fall to evade
attack of the fly. While these experiments have not been going on
fora long enough time to give results sufficiently definite, covering
all variations in the weather during these months, it is safe to say that
wheat may probably be sown, without danger from Hessian fly attack,
in northern Michigan soon after the first of September; in southern
Michigan and northern Ohio, about September 20; in southern Ohio,
after the first week in October; in Kentucky and Tennessee, October
10 to 20; in Georgia and South Carolina, October 25 to November 15.
‘So far these dates are only approximate, and serve to show ina general
way about the time when the fall brood of the fly will have largely disap-
peared over the wheat belt east of the Mississippi River. As the
larger part of the fall brood appears and is gone within a week, it is
possible for a farmer to so time his seeding as to avoid it, and this is
by far the most practical and effective preventive measure that can be
applied.

CROP ROTATION.

Aside from the general benefits to be derived from crop rotation, it
compels the Hessian fly, when it emerges from the stubble in the fall
(or spring in the Northwest) to travel a greater or less distance to
reach young wheat plants.

If, during this season of migration, storms or heavy winds occur,
these frail creatures will be driven about or beaten down until a com-
paratively small number survive to reach their destination. On the
other hand, if they are not obliged to leave the field where they
emerge, this mortality will be vastly lessened.

BURNING STUBBLE.

This is the most efficient measure of all, as fire will reach and
destroy not only the Hessian fly but all other insects infesting the
stubble, including the joint-worm. Unfortunately, it can not be gen-
erally carried out. Over a large portion of the Middle West timothy
and clover are sown, either with the wheat or during late winter or
early spring, and therefore stubble-ground can not be burned over.
Fields not followed by grass or clover can usually be burned over if
the grain is cut rather bigh at harvest and a mower is run over the
field and the mown grass, weeds, and stubble allowed to dry for a few
days just before the burning. This is much the more feasible measure
in the Northwest, and ought to be more generally followed.

15

DESTRUCTION OF VOLUNTEER WHEAT.

Perhaps the importance of this measure is best illustrated by the
condition frequently observed in fields of young wheat in the fall,
where every volunteer plant is infested and the sown grain is entirely
free from attack. The volunteer plants were above ground in time
to enable the fly to deposit her eggs on them, with the result that large
numbers of flaxseeds will go through the winter and the flies there-
from will deposit their eggs on the plants which constitute the crop
itself. Thus the growth of volunteer plants menaces, to a certain
degree, the crop of the following year, precisely as does a field sown
too early more seriously menace adjoining fields that are uninfested
in the fall. This destruction of volunteer plants by plowing, disking,
or otherwise must take place before the larvee have matured in order
to be effective.

ENRICHING THE SOIL.

While it may seem ‘‘ far fetched” to bring forward as a preventive
measure the enrichment of the soil, a fertile soil will produce plants
that will withstand with little injury attacks that will prove disastrous
to plants growing on an impoverished or thin soil. This is because a
fertile soil will enable an infested plant to tiller freely, and these tillers
will have sufficient vitality to withstand the winter and send up head-
producing stems in the spring. It is also chiefly on the thin or impov-
erished soils that the difficulty of sowing late enough to evade the fall
attack and at the same time secure a growth suflicient to withstand
the winter is encountered, and whatever can be done to obviate this
difficulty will constitute a preventive measure.

PROPER PREPARATION OF THE SOIL.

It matters little whether a soil has much or little fertility if that
fertility is bound up in clods or hard lumps out of reach of the root-
lets of the young plants. Early plowing and thorough working and
compacting of the soil will eliminate the lumps and clods and produce a
finely pulverized, compact, moisture-conserving seed bed, from which,
as soon as rootlets are sent out from the seed kernel, the shoot will
begin to draw nourishment. This will give vigor to the plants and
thus enable them, by freely tillering, to outgrow a light attack of the
fly that otherwise might prove serious.

THE USE OF GOOD SEED.

When we come to consider the fact that the seed kernel contains, or
should contain, sufficient nutriment to put out and sustain rootlets
until these can begin to draw from the soil and thus support the stem,
it will be seen at once that any deficiency in the seed will necessarily
tend to weaken the plant at the very beginning of its existence. Thus

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good seed becomes the first requisite in securing the healthy, vigorous
plant that is to be further strengthened and sustained by a well-
prepared, fertile soil. It is very clear, then, that all shrunken,
dwarfed, or otherwise imperfect kernels should be cleaned out of the
seed before it is sown and only the largest and most perfect retained.

CONCLUSION.

Methods for controlling the Hessian fly, the worst pest of the wheat
field, in the fall wheat growing sections, may be summarized as fol-
lows: Sow the best of seed in thoroughly prepared, fertile soil after
the major portion of the fall brood has made its appearance and passed
out of existence, and, if possible, sow on ground not devoted to wheat
the preceding year.

In the spring-wheat section late seeding will not apply. It seems
likely, on the contrary, that the earlier it is sown in spring the less it
will suffer from the Hessian fly. But good seed and a well-prepared,
fertile soil are as essential there as elsewhere.

Approved:

JAMES WILSON,
Secretary of Agriculture.

WasuineTon, D. C., April 14, 1906.

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