PEACH LEAF-CURL 
This is a common and frequently destructive disease of peaches in 
nearly every peach-growing section. It is especially severe in regions 
subject to cold, wet weather in the spring. One of the most profitable 
commercial varieties, the Elberta, is particularly susceptible. 
SYMPTOMS 
It is chiefly a disease of the leaves, although the current season’s shoots 
may also suffer. Shoot-infection is especially serious when nursery-stock 
is affected. Flowers and fruit rarely show lesions of the disease. 
On the leaves. Examine the material provided. OBSERVE :— 
1. The flexible character of the normal portions of the leaf. 
Tear it and note the texture. 
2. The wrinkled and distorted portion of the leaf affected by the 
curl. Tear and compare with the healthy portion as to texture and 
flexibility. Explain the difference. Compare with the healthy portion 
as to color and thickness. 
3. The character of the distortion. In which direction as re- 
gards the long axis is the diseased leaf wrinkled? Why? prRaw. 
Examine photographs and Cornell Bul. 276, fig. 83-86. OBSERVE :— 
4. That the diseased leaves soon drop, partially or wholly 
defoliating the tree. Later new leaves are usually put forth. 
On the twigs. Study the specimens provided. OBSERVE :— ; 
5. The dwarfing of the shoot due to a shortening of the inter- 
nodes, giving it a rosette-like appearance. 
6. The much thickened fleshy stem,—hypertrophied; more or 
less definite linear ridges often extending down on the previous years 
growth. 
7. The badly infected leaves. The leaves on diseased twigs 
are more severely affected than on the healthy twigs, for invasion becomes 
general or systemic and the leaf-fundaments become diseased as they 
are formed. Most of the affected shoots gradually die. (Compare U. S. 
Agr. Dept., Veg. Phys. and Path. Div. Bul. 20, pl. V.) 
On flowers and fruit. If specimens or photographs are available, study 
the character of the lesions on these organs. DRAW. ; 
The curl on the leaves affects the fruit indirectly by preventing setting 
or by causing it to fall. (Study U. S. Agr. Dept., Veg. Phys. and Path. 
Div. Bul. 20, pl. XVII, and table 33, p. 124.) 
ETIOLOGY 
The cause of this curl is Exoascus deformans (Berkley) Fuckel, one 
of the primitive ascomycetes of the order Protodiscales. No definite 
fruit-body is formed, the asci developing directly from the mycelium in an 
exposed hymenium over the surface of the lesion. ; 
Life-history. Relatively little is positively known about. the life- 
history of E. deformans. Opinions with respect to the life-habits of this 
pathogene are based very largely upon circumstantial evidence. No 
true asexual stage of the fungus is known. 
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