DISEASES OF CROPS 



943 



which a sticky, milky fluid oozes in the early spring, and from which the 

 disease is spread, by means of insects, to the opening blossoms. If the 

 weather conditions are favorable the blossoms and fruit spurs die and 

 blacken and very frequently considerable quantities of the young fruit are 

 destined. The disease also occurs on the apple, crab, hawthorn and 

 other related trees. 



Treatment. — Prune and burn the diseased twigs on young trees; 

 clean out the cankers on old trees, dipping the knife from time to time in 

 formaldehyde (1 part in 20 parts water). Paint these wounds with formal- 

 dehyde and then with white lead paint or coal tar. Do not over-fertilize 

 or over-cultivate the orchard. 



Spray Table for Apples, Pears and Quinces. 



Two additional sprayings are frequently necessary for fall and winter varieties. 



Arsenical poisons for chewing insects and tobacco extracts for sucking insects may be added to treatments 2 and 3. 



Rust (Gijmnosporangium juniperi-virginianae and G. blasdaleanum 

 [D. and H.], Kern). — Similar to apple rust. 



Scab (V. pyrina, Aderh.). — Similar to apple scab. 



Leaf Spot (Septoria pyricola, Desm.) appears as numerous small, well- 

 defined, angular, ashy-colored spots with minute black dots. It is not often 

 severe. 



Leaf Spot (Entomosporium maculatum, Lev.) occurs on the leaf, causing 

 small, circular spots with dull, red centers and dark borders. When severe 

 it causes the leaves to become yellow or brown and fall. It also attacks 

 the fruit, causing spots which are at first red, becoming dark and in severe 

 cases causing the fruit to crack. It is carried over the winter on the fallen 

 leaves. 



Treatment. — This disease can be controlled by spraying with Bordeaux 

 mixture, beginning when the leaves are about half or two-thirds full grown 

 and repeating at intervals of three weeks until four treatments have been 

 given. 



Rots. — The black rot and brown rot also occur on the pear. (See 

 Apple.) 



Crown Gall. — See Apple. 



