86 
WISCONSIN HORTICULTURE February, 1917 
Clean Cultivation and Thorough 
Spraying Promise Most Re- 
lief from Cherry Leaf Spot 
Sturgeon Bay, Jan. 17 — At a 
meeting of Door county fruit grow- 
ers held on Wednesday, January 
17, C. W. Keitt, of the department 
of plant pathology of the Univer- 
sity of Wisconsin, reported, upon 
investigations looking toward the 
control of cherry leaf spot which 
have been in progress here and at 
the Experiment Station for the 
past two years. 
Leaf spot (also called “shot- 
hole” or “yellow leaf”) is one of 
the most serious pests of the cherry 
in Wisconsin, and, unless controll- 
ed, makes the piofitable culture of 
this fruit impossible in our more 
important cherry producing sec- 
tions. For many years Wisconsin 
cherry growers have been able to 
control this disease by persistent 
spraying with Bordeaux mixture. 
However, the time and number of 
applications and the concentration 
of the spray necessary for best and 
most economical results have not 
been determined, and in certain 
years the foliage of many Bor- 
deaux sprayed orchards has failed 
to go through the season satisfac- 
torily. Furthermore, the high 
price of copper sulphate and the 
scarcity of labor have made it very 
important that the expense of the 
treatment be reduced. Conse- 
quently, there has been legitimate 
call from the cherry groAvers of 
the state for investigation of this 
disease with the aim of determining 
the most economical methods by 
which it can be efficiently controll- 
ed under Wisconsin conditions. 
Laboratory and field studies have 
been conducted at Madison, and 
for two seasons a field station has 
been maintained here at Sturgeon 
Bay. Mr. Keith expressed his ap- 
preciation to the people of Stur- 
geon Bay for haA T ing greatly aided 
the work by placing the laborator- 
ies of the high school at the dis- 
posal of the investigators during 
the summer months, and by cooper- 
ating individually in various lines 
of experimental A\ r ork. 
ATTACKS FOLIAGE AND FRUIT 
“The leaf spot disease,” said 
Mr. Keitt, “affects not only the 
foliage, but also the fruit. On the 
leaves, it appears as small round- 
ish broAvn spots which often oc- 
cur so abundantly that they run 
together and form large irregular 
dead patches. Under certain con- 
ditions, the dead spots -drop out 
and on account of the resulting 
appearance of the leaves the disease 
has often been called shot-hole. 
Badly affected leaves ordinarily 
turn yelloAv and drop. This has 
led many to call the disease yel- 
low leaf. It should be borne in 
mind, hoAvever, that certain other 
troubles may have very similar 
symptoms, and that there is dan- 
ger o<f confusing leaf spot Avith 
other foliage injuries. In cases of 
doubt, specimens should be sent 
to the department of plant pathol- 
ogy of the university for identifi- 
cation. On the fruit or the pedi- 
cels (stems of the fruit,) the dis- 
ease may appear as small broAvn- 
ish or reddish spots. The chief in- 
jury to the fruit, however, results 
from the loss of vitality of the 
tree, due to the effect of the disease 
on the leaves. In case of severe 
attacks, the fruit may fail to ma- 
ture, and Avood and bud formation 
are seriously hindered. Repeated 
severe attacks may kill the tree. 
DEAD LEAVES HARBOR THE DISEASE 
“Leaf spot is caused by a fun- 
gus (a Ioav form of plant) which 
lives in the diseased parts of the 
cherry in the summer and passes 
the winter in the dead leaves on 
the ground. In the spring, it pro- 
duces spores (Avinter spores), like 
the seeds of higher plants, but too 
small to be seen Avith the unaided 
eye, which are carried in the air 
and lodge on the leaves. Here they 
germinate, groAv into the leaf, and 
produce the disease. On the under 
surfaces of the resulting spots 
small “blisters” usually develop. 
These break open and a Avhitish 
material oozes out. This is made up 
of thousands of spores of another 
type (summer spores) Avhich serve 
to spread the disease very rapidly. 
INTIMATE ACQUAINTANCE NECESSARY 
“In order to fight the disease to 
best advantage, it is necessary to 
knoAv not only its cause, but also 
a great many facts concerning its 
development. It is necessary to 
knoAv the condition of the fungus 
throughout the year, Avhen and 
Avhere it produces spores, how these 
are scattered, hoiv they produce in- 
fection, what plants harbor the dis- 
ease, Avhat conditions favor or hin- 
der its development, and the like. 
Many of these matters haA r e already 
been determined and others are be- 
ing studied further. The informa- 
tion thus obtained not only prom- 
ises to be of much A’alue in working 
out the most economical and effi- 
cient spray treatments but in de- 
veloping a further method of fight- 
ing the disease, as follows : 
EARLY CLEAN CULTIVATION HELPFUL 
‘ ‘ The studies of the leaf spot 
fungus have shoAA’n that the Aveak- 
est point in its life history occurs 
A\iien it passes the winter in the 
dead leaves on the ground. If all 
these dead leaves would be de- 
stroyed, and if the disease harbored 
on no other plants, spraying Avould 
not be necessary. While it is not 
practicable to dispose of the dead 
leaA r es in such a AA r ay as to make 
spraying unnecessary, it is possible 
greatly to strengthen the spray 
schedule, and probably eventually 
to cut doAvn the number of appli- 
