S

s blicatjons
3 :ived

p

New Integrated
Approach for
Controlling X-disease
of Stone Fruits

P OF CONNECTICUT

BY SHARON M. DOUGLAS
AND MARK S. McCLURE

February 1988

Digitized by the Internet Archive

in 2011 with funding from

LYRASIS members and Sloan Foundation

http://www.archive.org/details/newintegratedappOOdoug

New Integrated Approach for Controlling
X-disease of Stone Fruits

BY SHARON M. DOUGLAS
AND MARK S. McCLURE

Despite its presence as a pest in the United
States for more than 50 years, X-disease of
stone fruits continues to be destructive and
uncontrolled in fruit-growing areas, including
many regions of Connecticut. This disease
causes substantial economic losses in peach and
other stone fruits, including nectarine, Japanese
plum, sweet cherry, and sour cherry. Disease
incidences as high as 60% and yield reductions
ranging from 30% for mildly symptomatic to 80%
for severely symptomatic trees have been
observed in some commercial peach plantings in
Connecticut.

X-disease was first observed in the eastern
United States in 1933 when Stoddard found it in
a Connecticut peach orchard (20). In his
pioneering work, Stoddard described and named
this new disease of peach, and his investigations
completed a framework for understanding many
of the factors associated with this disease
(Figure 1) (21). Concurrent with Stoddard's work
in Connecticut, workers in California described
diseases of cherry and peach which had
characteristics similar to X-disease (15,22).
These eastern and western forms of X-disease
were initially considered distinct diseases, but
when strains from several regions of North
America were compared experimentally, it was
concluded that all were strains of the same
disease (6). X-disease, in a variety of forms,
has been reported in at least 26 states and three
Canadian provinces (4).

At the time of its description, the causal
agent of X-disease was thought to be a virus
which could only be successfully transmitted by
budding and grafting, not by mechanical
inoculation (20,21). Mycoplasm alike organisms
(XMLO) were first associated with the disease in

FIGURE 1— Photograph taken August 31, 1933 by
Ernest Stoddard who described this as an "unusual
peach disease. ..cause of trouble not yet
determined". Note tattered, shot-holed peach
leaves characteristic of X-disease.

Connecticut Agricultural Experiment Station

Bulletin 854

. ■-.■&.:.'■£>

FIGURE 2— Electron micrograph showing phloem
cells of an X-diseased peach petiole packed with
many mycoplasmalike organisms (arrows) which
are 0.5 urn or 1/100,000 of an inch in diameter.

1970 when they were observed in infected tissue
using electron microscopy (14). These organisms
comprise a relatively new class of disease agents
which are similar to bacteria but which lack a
cell wall and are limited to growing in the
phloem of plant hosts (Figure 2). In fact, XMLO
cannot survive outside of their plant hosts or
insect vectors. Although attempts to culture
XMLO in -\dtro have been unsuccessful, additional
evidence has subsequently supported their role in
X-disease including further electron microscopy
(7), symptom remission after tetracycline
chemotherapy (19), and eradication of XMLO in
budwood by heat treatment (21).

leaves of X-diseased peach trees are usually
normal in appearance at the start of the growing
season, but there is a sudden onset of symptoms
by mid-summer. Leaves develop yellow or red
irregular blotches and roll upward longitudinally.
Discolored areas become dry and brittle and dead

tissue drops out giving affected foliage a
tattered appearance. Symptomatic leaves usually
abscise, leaving a rosetted tuft of leaves at the
terminals (Figure 1). X-disease also reduces the
growth and vigor of fruiting wood from both
symptomatic and non-symptomatic portions of
infected trees, even in the early stages (3).
Diseased trees eventually become unproductive
with insipid, bitter tasting or aborted fruit; trees
of any size or age can be affected. Besides
direct economic losses, orchardists have the costs
of removing and replacing dead or severely
affected trees and the 3-4 year wait for
replacements to reach commercial bearing.

Initial observations of orchard trees in
Connecticut indicated that the first trees to
exhibit X-disease symptoms were located at or
near the edge of the orchard (20). This led to
the conclusion that infection might originate from
a wild host plant in the adjacent wood lot or
fence row. Stoddard (20) identified chokecherry,
Primus virginiana, as a reservoir host of the
X-disease agent on the basis of changes in
foliage color similar to those exhibited by
foliage of X-diseased peach. Soon thereafter,
researchers speculated that the X-disease agent
was transmitted from this infected wild host to
peach by insects.

Over ten species of leaf hoppers, small
piercing and sucking insects (Figure 3), were
demonstrated to transmit the X-disease agent
throughout the United States (4,5,16,18). These
leafhoppers are phloem feeders and they acquire

FIGURE 3— Leafhopper stylet penetrating a
petiole. Note the dark ring at the site.

Integrated Approach for Controlling X-disease

XMLO during feeding. The relative importance
of each species is influenced by their biology,
especially feeding and egg laying preferences.
MeClure documented the occurrence and seasonal
distribution throughout Connecticut of six vector
species using yellow sticky traps (10). These
included Colladonus clitellarius , Fieberiella florii,
Gyponana lamina, Norvellina seminuda,
Paraphlepsius irroratus, and Scaphytopius acutus.
These leafhoppers were most abundant in peach
orchards which had wild host plants in the
ground cover and at the orchard edge (11).
Researchers have found that orchard blocks with
the most leafhoppers generally had the most
X-disease (17).

Additional experiments at the Station
demonstrated the influence of ground cover type
on the number of leafhoppers which visited peach
trees. S. acutus was reported to be the most
abundant and widespread vector in commercial
Connecticut orchards and it was most highly
attracted to red clover for both feeding and egg
laying (10,11,12). MeClure and co-workers (13)
found that invasion of peach trees by vectors
could be reduced by manipulating the type of

ground cover around each tree. The greatest
numbers of adults were trapped in plots with
pure red clover as ground cover; significantly
fewer leafhoppers, in order of decreasing number,
were trapped in plots with ground covers
consisting of mixed weeds of mainly roseaceous
species (i.e., raspberry, strawberry), pure orchard
grass, or bare ground. They speculated that
reduced numbers of vectors might reduce
incidence of disease, but did not test this
hypothesis.

The cycle of X-disease is complex (Figure 4).
Eggs of leafhoppers hatch in spring and nymphs
develop on weeds at the edge of the orchard or
in wood lots. These leafhoppers are thought to
feed on nearby X-diseased chokecherry, the key
reservoir host, where the leafhoppers acquire the
XMLO. Seasonal changes in vector preferences
for feeding and egg laying subsequently encourage
dispersal of the adults into the orchard and
stimulate movement among various ground cover
species and peach trees. In addition to
influencing leafhopper movement into an orchard,
ground cover species (e.g., wild strawberry, wild
carrot) have been implicated as reservoirs of

X-DISEASED
CHOKECHERRY

PEACH

ORCHARD GROUND COVER

FIGURE 4— The X-disease cycle. Arrows represent the movement of
leafhopper vectors from the orchard edge (X-diseased chokecherry) into the
orchard and between ground cover species and peach trees.

Connecticut Agricultural Experiment Station

Bulletin 854

XMLO and are thought to have important roles
in the epidemiology of X-disease (1).

Past approaches to the control of X-disease
have targeted the plant hosts and have not
considered the insect vectors. These traditional
control strategies included removing chokecherry
in the vicinity of orchards (9,20,21), removing or
pruning diseased orchard trees (6), and treating
diseased trees with an antibiotic (19). Although
these approaches have helped retard the spread
of X-disease, they have not given orchardists
satisfactory control. In addition to these
measures, researchers have suggested management
of leafhopper populations by use of insecticides
(18) or by ground cover type (13), but the
effectiveness of such measures in controlling
disease is not known. In light of the growing
need for more effective control of
X-disease in Connecticut, we conducted
experiments from 1981-1984 to determine the
impact of manipulating ground cover type on
populations of leafhopper vectors during the
growing season and over a period of several
years, to determine if ground cover affects
vector feeding on peach leaves, and to determine
if these factors influence the spread of disease.

MATERIALS AND METHODS

In April 1981, 256 one-year-old peach trees
(cv. Blake) were planted at the Station's
Lockwood Farm in Kamden, Connecticut. The
experiment was set up with two treatments, bare
ground and weedy cover, which were each
replicated eight times so there were eight plots
with weeds and eight plots with bare ground in
the grid (Figure 5). Each plot measured 335 m
sq. and contained 16 trees which were equally
spaced 3.6 m apart. Bare ground was maintained
throughout the experiment by herbicide
treatments and hand weeding. Weedy cover
consisted of naturally occurring plant species
which were occasionally mowed during the
experiment to maintain height at 1 0.5 m.

Bright yellow, sticky paper traps (Zoecon
Pherocon AM Traps) measuring 23 X 28 cm
(644 cm sq.), which are attractive to adult
leafhoppers, were placed on stakes 1 m above
the ground in the center of each of the 16
plots. Traps were replaced at 14-day intervals
from June through October for a total of

t
N

• • • •

w

® • • •

W

B

B

W

*B® '

W

(a>

W

B

W

B

• • • •

B

W

B

W

FIGURE 5— Diagram illustrating the arrangement
of the experimental plot. B=bare ground,
W=weedy cover; solid dots=healthy trees, and X=
X-diseased trees.

ten intervals each growing season. The number
of each vector species was counted.

In late June and late September 1983, sweep
samples were taken in each plot using a 0.5 m
diameter sweep net. Each of four trees along a
NW to SE transect (Figure 5) were swept five
times per tree. In weedy plots, the ground
cover beneath each of these four trees was also
swept five times. The numbers of leafhopper
vectors captured were recorded for comparison
with sticky trap catches.

Leafhopper feeding damage to peach leaves
was assessed once or twice each year after
vector population peaks. Twenty leaves (five
leaves each from four sides of a tree) were
removed from each of four trees along a SW to
NE transect (Figure 5) through each plot.
Leaves were examined for the presence of
stipling, which is evidence of leafhopper feeding.
The numbers and kinds of leafhoppers observed
feeding on peach leaves at the time of sampling
were also recorded for comparison with sticky
trap and sweep net samples.

Each August, all trees were visually assessed
for symptoms of X-disease.

Integrated Approach for Controlling X-disease

RESULTS

All six leafhopper vectors of X-disease
previously reported in Connecticut (10) were
captured during the four years of this study. Of
the tot8l 4,731 adult vector leafhoppers trapped
on yellow sticky traps, 81-94% were captured in
plots with weeds as compared with 6-19% in
plots with bare ground (Table 1). The difference
in the number of leafhoppers trapped in plots
with these two types of ground cover was highly
significant (R = 0.98) for each year. Numbers of
individual leafhopper species trapped in weedy
and bare ground plots followed the same pattern
for total leafhoppers. P. irroratus was by far
the most abundant species (79% of total), and
S. acutus was a distant second (10%); each of
the other vector species comprised less than 8%
of the total leafhoppers trapped (Table 1).

TABLE 1— LEAFHOPPERS1 CAPTURED ON
YELLOW STICKY TRAPS IN PLOTS WITH BARE
GROUND OR WEEDY COVER.

100

3

g

O

z

Q

O

JUN JUL AUG SEP OCT

TRAPPING INTERVAL

FIGURE 6— Mean seasonal abundance (1981-1984)
of leafhopper vectors trapped in plots with bare
ground (solid line) or weedy cover (dashed line).
Bars represent amount of feeding damage to
peach leaves in bare (solid bar) and weedy
(slashed bar) plots.

Bare Ground

Weedy

Cover

Year

Number

%

Num

ber %

1981

278

19

1169

81

1982

230

15

1305

85

1983

38

6

639

94

1984

133

12

939

88

Six X-disease vectors and relative abundance
(%): Paraphelpsius irroratus (79), Scaphytopius
acutus (10), Gyponana lamina (7), Colladonus
clitellarius (2), Norvellina seminuda (1), and
Fieberiella florii (1).

Data from leafhopper sticky trap catches for
all four years revealed two distinct peaks of
abundance (Figure 6). The magnitude of the
second population peak (late September) was as
much as six times greater than that of the first
peak (late June). Lowest numbers of adult
leafhoppers occurred during mid-August. Patterns
for peaks of abundance were the same, albeit
different in magnitude, whether leafhoppers were
trapped in plots with bare ground or with weeds.

Numbers of vector leafhoppers collected with
sweep nets from peach trees and weeds in weed-
cover plots and from peach trees in bare ground

plots during the two sampling periods were small
(n=76). However, more leafhoppers were
collected in weedy than in bare plots and more
were caught in September (2nd peak) than in
June (1st peak), as with sticky trap catches.
Four of the six X-disease vector species were
represented in these sweep samples, and patterns
were similar to sticky trap catches; P. irroratus
was the most prevalent species (75% of total).
Absent from sweep samples were F. florii and
N. seminuda.

The amount of feeding damage on leaves
from trees in weedy plots was significantly
greater than on leaves from trees in bare ground
plots for all years of this study, regardless of
when damage was assessed (Table 2). Our data
defined a relationship between numbers of
leafhopper vectors and amounts of feeding
damage: higher numbers of leafhoppers were
associated with greater levels of damage
(R = 0.90) (Figure 7). Levels of damage were
also consistent with our previous observation of
two peaks of leafhopper abundance. In 1983 and
1984, the mid-summer peak accounted for only
14-22% of the cumulative damage as compared
with the fall peak which accounted for 56-78% of

Connecticut Agricultural Experiment Station

Bulletin 854

TABLE 2— CUMULATIVE LEAFHOPPER FEEDING
DAMAGE ON PEACH LEAVES IN PLOTS WITH
BARE GROUND AND WEEDY COVER.
NUMBERS ARE MEANS (+ S.E.).

Date

11/82
8/83

10/83
8/84

10/84

% LEAVES WITH FEEDING DAMAGE
Bare Ground Weedy Cover

22.7

(±1.1)

0.7

(±0.3)

14.1

(±1.6)

1.4

(±0.9)

22.0

(±1.6)

93.3
9.9

56.9
9.5

78.3

(±1.3)
(±0.4)
(±2.1)
(±0.5)
(±1.6)

overall feeding damage (Figure 6). The mean
total damage was greater in weedy than in bare
plots, reflecting similar trends in numbers of
leafhoppers trapped in those plots. Representa-
tives from most of the six vector species were
observed feeding on peach leaves during our
study. Our observations were once again
consistent with data from sticky trap and sweep
net catches. P. irroratus was most commonly
observed (82% of total), followed by S. acutus
(9%). Other leafhoppers not known to vector
X-disease were also observed on peach foliage
and captured on sticky traps, but their numbers
were few compared to vector leafhoppers.

100 r

Y = 0.059 X + 2.96
R'= 0.90

"i 1

o

700
NUMBER OF LEAFHOPPERS

1400

FIGURE 7— Relationship between number of
leafhoppers trapped in plots with bare ground
(solid diamond) and weedy cover (open diamond)
and amount of feeding damage on peach leaves.

The number of trees with symptoms of
X-disease by August 1985 was too small in both
weedy (2 trees) and bare ground (5 trees) plots
to determine significant differences. However,
four out of five of the trees with X-disease
symptoms in bare ground plots were border trees,
located next to weedy plots (Figure 5).

DISCUSSION

Our study reaffirmed the importance of
ground cover type to the size of leafhopper
vector populations. But, more importantly, it
established a relationship between leafhopper
numbers and amount of feeding damage to peach
leaves: higher numbers of vectors were associated
with greater amounts of feeding damage. These
findings emphasize the need to adopt a more
integrated approach for controlling X-disease than
has traditionally been undertaken. Such an
approach includes both cultural and chemical
measures and takes into account not only the
disease agent and its numerous plant hosts but,
for the first time, also includes the leafhoppers
which carry and vector XMLO.

The low incidence of X-disease (3%) in the
four years of our experiment is not unusual.
For example, our results are consistent with
observations from several commercial orchards of
similar age and over a similar period of time
which revealed 4% of the trees had X-disease in
4 years (Douglas, unpublished). When evaluating
the importance of a disease such as X-disease
that has an apparently low infection rate, it is
necessary to consider that peach treees are
perennial and once infected, will remain infected
until death. Consequently, small numbers of new
infections each year can effectively reduce
productivity by shortening the normal lifespan of
a peach block. In this light, all efforts aimed
at interrupting the X-disease cycle are important
for disease control.

Some of the cultural control measures that
have been used for years are important
components of our integrated approach. Removal
of X-diseased chokecherry within 152 m of a
peach planting (9,20,21) and removal of diseased
peach trees or pruning of affected parts (6)
continue to be prudent practices for reducing the
X-disease inoculum in and about the orchard.

Results of this and previous studies (11,12,13)

Integrated Approach for Controlling X-disease

reveal that management of ground cover in the
orchard is also an effective cultural measure for
reducing leafhopper vector populations and feeding
damage to peach. In general, vector leafhoppers
thrive in ground covers that are comprised
mostly of red clover or roseaceous species (e.g.
raspberry, strawberry). All vector leafhoppers
are discouraged from invading the orchard if
unfavorable conditions for leafhoppers are
maintained in the orchard floor by regular
mowing, by planting unsuitable host species, or
by keeping the ground bare through use of
herbicides and by weeding. All species except
P. irroratus also find a cover of pure orchard
grass highly unsuitable for their needs (12).
Studies have shown that the condition of the
orchard floor directly beneath each peach tree is
important because leafhopper movements between
peach trees and ground cover species in response
to feeding and breeding preferences are localized
(13). These cultural measures will provide the
additional benefit of eliminating potential
reservoirs of XMLO which are apt to be common
in the herbaceous weedy ground cover of a peach
orchard. Our results have also shown that
maintaining bare ground beneath peach trees
gives the added advantage of enhancing growth
and yield by eliminating competition for moisture
and nutrients from ground cover. In fact, mean
trunk diameter measurements (1985) for trees in
plots with bare ground were 6.6 cm as compared
with 3.6 cm for their weedy counterparts.

Earlier studies have shown that vector
leafhoppers overwinter in the leaf litter and
mature on the weedy and woody vegetation
(primarily roseaceous plants) at the edges of the
orchard in the spring (10,11,12). This coincides
with the time during which detectable levels of
XMLO are present in diseased chokecherry (2).
In June, adult leafhoppers, some of which are
probably carrying XMLO, invade the orchard and
colonize both peach trees and ground cover
species. Removal of the leafhoppers' spring
hosts (especially roseaceous species) from the
orchard edge is another important cultural control
practice aimed at reducing vector populations
before they enter the orchard.

Several chemical control measures targeting
either the disease agent or the vector
leafhoppers complement these cultural practices
in our integrated control scheme for X-disease.

Antibiotics, in particular oxytetracycline-KCl used
annually as a tree injection (19), prolong the
productive life of diseased trees. Other chemical
procedures for reducing the spread of X-disease
involve insecticides which target vector
leafhoppers (8). Most routine insecticide
treatments of peach trees are applied between
petal fall (May) and harvest (August). These
treatments probably have minima] effects on
leafhoppers present in the ground cover or at the
orchard edge and essentially leave no residual on
peach trees after harvest. Since results of this
and previous studies (10-13) have shown that
weedy species in and around the orchard harbor
high numbers of leafhoppers, periodic insecticide
treatments of weedy ground cover and of weedy
vegetation at the orchard edge should reduce
numbers of vector leafhoppers.

Our study also showed leafhopper densities
and feeding damage on peach were much higher
in September and October following harvest than
at any other time of the year. Even if only a
small percentage of these leafhoppers are
actually carrying XMLO, this period should be
important for the spread of X-disease because of
the intensity of feeding. Therefore, insecticide
applications in and about the orchard during peak
leafhopper activity in early autumn could be
another effective means of reducing leafhopper
numbers and presumably, the spread of X-disease.
These autumn treatments would also reduce the
number of overwintering eggs and in so doing,
reduce the number of nymphs developing at the
orchard edge the following spring.

Briefly, the seven measures available for the
orchardist include: 1) removal of chokecherry;

2) removal and pruning of X-diseased peach;

3) removal of spring hosts of leafhoppers
(especially roseaceous species) at the orchard
edge; 4) management of orchard ground cover
during the growing season by planting unsuitable
species for leafhoppers, by mowing, and by
herbicide treatments; 5) periodic insecticide
sprays applied to ground cover during the growing
season; 6) antibiotic injections of peach; and 7)
additional insecticide sprays to peach trees after
harvest (during September and October).

Because of the complexity of the X-disease
cycle, we cannot expect to effectively control
the disease with a simple solution. We are
continuing to unravel the mysteries of the

10

Connecticut Agricultural Experiment Station

Bulletin 854

complex system involving the X-disease
mycoplasmalike organism, its vector leafhoppers
and the numerous plant species including peach,
which they share. Until then, the multifaceted
approach for controlling X-disease that integrates
both cultural and chemical measures may help us
to continue to grow peaches in the midst of this
destructive disease.

REFERENCES

1. Chiykowski, L.N. and Sinha, R.C. 1982.
Herbaceous host plants of peach eastern X-
disease. Can. J. PI. Pathol. 4:8-15.

2. Douglas, S.M. 1986. Detection of
mycoplasmalike organisms in peach and
chokecherry with X-disease by fluorescence
microscopy. Phytopathology 76:784-787.

3. Douglas, S.M. 1986. Initial stages of X-
disease in peach: Within-tree spread and effects
on growth. Phytopathology 76:1084.

4. Gilmer, R.M. and Blodgett, E.G. 1976. X-
disease. In Diseases and Noninfectious Disorders
of Stone Fruits in North America. USDA
Handbook 437. pp. 145-155.

5. Gilmer, R.M., Palmiter, D.H., Schaefers, G.A.,
and McEwen, F.L. 1966. Insect transmission of X-
disease virus in stone fruits in New York. NY
State Agric. Exp. Stn. Bull. 813 (Geneva). 22pp.

6. Hildebrand, E.M. 1953. Yellow-red or X-disease
of peach. Cornell Univ. Agric. Exp. Stn. Mem.
323. 54pp.

7. Jones, A.L., Hooper, G.F., and Rosenberger,
D.A. 1974. Association of mycoplasmalike bodies
with little peach and X-disease. Phytopathology
64:755-756.

8. Lacy, G.H. 1982. Occurrence and seasonal
distribution of leafhopper vectors of the X-
disease causal agent in methoxychlor-sprayed and
unsprayed peach orchards. Crop Protection 1:333-
340.

9. Lukens, R.J., Miller, P.M., Walton, G.S., and
Hitchcock, S.W. 1971. Incidence of X-disease of
peach and eradication of chokecherry. PI. Dis.
Reptr. 55:645-647.

10. McClure, M.S. 1980. Spatial and seasonal
distributions of leafhopper vectors of peach

X-disease in Connecticut. Environ. Entomol.
9:668-672.

11. McClure, M.S. 1980. Role of wild host
plants in the feeding, oviposition, and dispersal of
Scaphytopius acutus (Homoptera: Cicadellidae), a
vector of peach X-disease. Environ. Entomol.
9:283-292.

12. McClure, M.S. 1982. Factors affecting
colonization of an orchard by leafhopper
(Homoptera: Cicadellidae) vectors of peach X-
disease. Environ. Entomol. 11:695-699.

13. McClure, M.S., Andreadis, T.G., and Lacy,
G.H. 1982. Manipulating orchard ground cover to
reduce invasion by leafhopper vectors of peach
X-disease. J. Econ. Entomol. 75:64-68.

14. Nasu, S., Jensen, D.D., and Richardson, J.
1970. Electron microscopy of mycoplasmalike
organisms associated with insect and plant hosts
of peach western X-disease. Virology 41:583-696.

15. Rawlins, T.E. and Home, W.T. 1931.
"Buckskin", a destructive graft-infectious disease
of the cherry. Phytopathology 21:33-35.

16. Rice, R.E. and Jones, R.A. 1972. Leafhopper
vectors of the western X-disease pathogen:
Collection in central California. Environ. Entomol.
1:726-730.

17. Rosenberger, D.A. end Jones, A.L. 1977.
Spread of X-disease in Michigan peach orchards.
PI. Dis. Reptr. 61:830-834.

18. Rosenberger, D.A. and Jones, A.L. 1978.
Leafhopper vectors of the peach X-disease.
Phytopathology 68:782-790.

19. Sands, D.C. and Walton, G.S. 1975.
Tetracycline injections for control of eastern X-
disease and bacterial spot of peach. PI. Dis.
Reptr. 59:573-576.

20. Stoddard, E.M. 1938. The "X-disease" of
peach. Conn. Agric. Fxp. Stn. (New Haven) Cir.
122. 7pp.

21. Stoddard, E.M. 1947. The X-disease of peach
and its chemotherapy. Conn. Agric. Exp. Stn.
(New Haven) Bull. 506. 19pp.

22. Thomas, H.E., Rawlins, T.E., and Parker,
K.G. 1940. A transmissible leaf-casting yellows of
peach. Phytopathology 30:322-328.

The Connecticut Agricultural Experiment Station ,

founded in 1875, is the first experiment station in America. It is chartered
by the General Assembly to make scientific inquiries and experiments
regarding plants and their pests, insects, soil and water, and to perform analyses for State
agencies. The laboratories of the Station are in New Haven and Windsor; its Lockwood
Farm is in Hamden. Single copies of bulletins are available free upon request to Pub-
lications; Box 1 106; New Haven, Connecticut 06504. ISSN 0097-0905

University of
Connecticut

Libraries

39153028932079

S^^Bh^h^H

' M ■••-.

mm

m

-■■'..

m$m%&

'•■>•'-■■■■■•■...
•-'-•■•-.,',

■■'".'■••' ': .■■■■•" ■ • '

■■ '

rLirEDJtUMjZBLrDiMTjiMi mi iij.f¥n.Br8TMTiiTfnBfirap ror i mn

•■.■■■■?•■••"'■",..•.•.•.-■•»•■'■'.■.-■•

•■■.-••.-'.'.■■.•"•■■■.,■ -v- ■"'.■■;■• f '■-.,-■ ■

- : ■ " V ' ■■ ' '.'■■' ^-: •• W -1 -,:;,/<•-: - ■'-• ■.

: ....■■■ s •■■.•■ I -.■■•'-.. ■•••■..- . • • : .•■.

•■■'■•'■>■

* - M

f«'?SwSs

»MSr;:'5(B*«?i«w

^^^^^^^i^a^y^i^^^»^^^w^^^^^^^^^^^^^^^™^ppj^p^^^^^i

'! -S ■■'';.■- v -. * . Kssranct

••••■.■.■'•••.<;•

: f^'-'h--r.:\

P|§^RH| I! HNpS

I

•.■•*-\;. '''■?£>'; ;.'-.:: ■.'■.'„•.:,,•,■ . '..V ■ ' '

K»

YW:' I •'

kKW|f!?»?i

nmrmrm

"•* * ' ■' "'■■■'■'■'-

, 'IBB

■' 8223

^BnMTV'tB-. A&&fl££nGDim$ #ra^toOT32C?«?i

9ffi wSBBBm

..■':-••■■.■

|§gp§ ..•■-'.

'■' ■■.;',','■ '• •.-.'

V; .' .''•'.-. : >.

■ '■'•>:.'■.•'• '.;■'"''-; ■

ise

sis"

'■■.;''.* •'•" ■''';'■ BRas :

■■ .'•■'■'■■?'' '"