April, 1918 
WISCONSIN HORTICULTURE 
117 
Control of Cherry Leaf Spot in 
Wisconsin* 
(i. W. Keitt 
Bulletin 286 Wisconsin Agricultural 
Experiment Station. 
*The matter presented in this bul- 
letin is to be accepted as a report of 
progress based upon two seasons’ 
work. It was Dr. Keitt's plan to con- 
tinue this work for a third season and 
present the detailed data in a re- 
search bulletin. Owing to his ab- 
sence in war service it has seemed 
best in order to meet the practical 
needs of the fruit growers to pub- 
lish the essential results in the present 
form. When conditions permit it is 
expected that the investigations will 
be completed and the full data pub- 
lished as originally planned. 
L. R. JONES, 
Professor of Plant Pathology. 
Leaf spot is the most serious fungus 
disease of the cherry in Wisconsin. 
Its control is necessary for profitable 
commercial cherry culture in this 
state. 
For many years Wisconsin orchard- 
ists have been able to control this di- 
sease by persistent spraying with 
Bordeaux mixture. However, the 
time and number of applications and 
the concentration of the spray neces- 
sary for the best and most economical 
results have remained to be deter- 
mined. Furthermore, the recent high 
prices of copper sulphate and the 
scarcity of labor have made it ex- 
tremely important to reduce the cost 
and labor of control measures and to 
develop, in case of need, a control 
program which is independent of 
Bordeaux mixture. 
The Nature of Leaf Spot Injury 
The leaf spot disease affects not 
only the foliage, but also the fruit and 
fruit stems. On the leaves, it ap- 
pears as small roundish spots which 
often occur so abundantly that they 
run together and form large irregular 
dead patches. Under certain condi- 
tions, the dead spots drop out and on 
account of the resulting appearance 
of the leaves the disease has often 
been called “shot hole.” Badly af- 
fected leaves ordinarily turn yellow 
and drop. This has led many to call 
the disease “yellow leaf.” It should 
be borne in mind, however, that cer- 
tain other troubles may show very 
similar symptoms, and that theie is 
danger of confusing leaf spot with 
other foliage injuries. On the fruit 
and the fruit stems the disease ap- 
pears as small brownish or reddish 
spots. The chief injury to the fruit, 
however, results from the loss of 
vitality of the tree, due to loss of 
leaves. In cases of severe attacks, 
the fruit often fails to mature, and 
wood and bud formation are seriously 
hindered. Repeated severe attacks 
may kill the tree. 
Leaf spot is caused by a fungus. 
Tl;is parasite lives in the diseased 
parts of the cherry plant in the sum- 
mer and passes the winter in the 
dead leaves on the ground. In the 
spring it produces spores (“winter 
spores”) which are shot into the air. 
Some of these lodge on living cherry- 
leaves. Here they germinate, grow 
into the leaf, and produce the disease. 
On the under surface of the result- 
ing spots, small “blisters” usually de- 
velop. These break open, and a 
whitish material ozzes out. This 
is made up of thousands of spores of 
another type ("summer spores”) 
which spread the disease very rapidly. 
Early Clean Cultivation 
Leaf spot may be fought by means 
other than spraying. The weakest 
point in the life history of the leaf 
spot fungus occurs when it passes the 
winter in the dead leaves on the 
ground. If all these dead leaves 
could be destroyed and if the fungus 
harbored on no other plants, spray- 
ing would not be necessary. While 
it is not practicable to practice sani- 
tation with such thoroughness as to 
make spraying unnecessary, it is pos- 
sible greatly to strengthen the spray- 
schedule by turning under as many 
of these leaves as is feasible by clean 
cultivation in the spring before the 
spores of the fungus are discharged. 
Our studies of the fungus have shown 
that “winter spores” usually begin to 
be discharged at about the time the 
blossom buds of the cherry begin to 
break open. Clean cultivation should 
precede this period. Most Wiscon- 
sin growers cultivate before this time 
anyway. Therefore, much may be 
gained with little additional expense 
by making the cultivation as clean as 
is practicable instead of leaving un- 
turned strips or large blocks about 
the bases of trees. 
Spraying 
The spray to use. The following 
sprays were tested comparatively: 
Bordeaux mixture (various strengths), 
lime-sulphur (various strengths), self- 
boiled lime-sulphur (8 lbs. lime and 
8 lbs. sulphur in 50 gals.), “atomic 
sulphur” (5 lbs. in 50 gals.), and 
“barium sulphur” (3 lbs. in 50 gals.) 
Four applications were made, approxi- 
mately as follows. ( 1 ) when the 
blossom buds showed white, just be- 
fore blooming, (2) just after the pet- 
als fell, (3) about two weeks later, 
and (4) just after the fruit was 
harvested. Similar tests were made 
in which the first treatment was 
omitted. Arsenate of lead powder 
( % to 1 lb. in 50 gals.) was added to 
the fungicide in each application. 
Bordeaux mixture and lime-sulphur 
controlled the disease very satisfac- 
torily. The other sprays tested fail- 
ed to control the disease satisfactorily. 
The results in the two years were con- 
firmatory. It is evident from these 
experiments that, under Wisconsin 
conditions, either Bordeaux mixture 
or lime-sulphur in combination with 
arsenate of lead, properly applied. 
FIG. 1— CHERRY LEAF SPOT 
Diseased leaves bear roundish brown spots, on the under surfaces of which “blisters” 
usually develop (right figure). These “blisters” are filled with spores, which rapidly 
spread the disease. Shch leaves usually turn yellow before they fall. Often the dead 
areas fall out and a “shothole” effect results. 
