128 PROCEEDINGS OF THIRTY-SIXTH FRUIT-GROWERS ' CONVENTION. 



colony, and to which they return when not feeding, but the canker- 

 worms live individually, and have the habit of spinning down from the 

 tree on a web when disturbed. 



The tussock caterpillar is capable of doing considerable damage even 

 when present in small numbers. This is due to the fact that it attacks 

 the young fruit, eating out portions which afterwards develop into 

 rough scars that detract much from the appearance and value. 



Treatment of caterpillars has to be modified according to their habits 

 and character. The. tent caterpillar and cankerworms are readily con- 

 trolled by spraying with arsenate of lead, and so no special treatment 

 need be given when applications are made for the codling moth. On 

 the other hand, the tussock caterpillar is not readily poisoned, and it 

 is more practical to pick the eggs from the trees during the winter 

 than to rely on arsenicals applied later. The eggs are laid in masses 

 about the size of a pea, and may be found on most any part of the 

 tree, often attached to the old cocoons. The white to gray color of the 

 egg masses makes it possible to find them rather readily, but very care- 

 ful work is necessary with large trees. 



Caterpillars are subject to great fluctuations in abundance, due to 

 the attacks of parasites and diseases. These natural enemies may 

 nearly exterminate the species at times, but again their absence for 

 several years allows a destructive increase of the pests. 



Coming now to the fungus diseases, the apple powdery mildew is the 

 most important. Under climatic conditions favorable to it, the per- 

 sistent attacks of this fungus keep the trees from making the proper 

 wood and foliage growth. The vigor of the tree is thus much reduced 

 and many unfavorable conditions develop. 



The mildew is a fungus parasite which thrives on the surface of 

 young leaves and growing shoots. It spreads over the attacked parts 

 and resembles a mold, both in appearance and odor. The fungus is 

 propagated and distributed by means of spores or seed-like bodies. 

 These spores, although microscopic, are produced in such enormous 

 numbers as to form a white powder, which is often abundant on mil- 

 dewed shoots. The spores are distributed by the wind. 



Treatment for the apple mildew has. until recently, been impractical, 

 because the fungicides in common use had little effect upon it. Winter 

 sprays have not proved effective because the fungus is in a very resist- 

 ant state during the dormant period. Sprays, to be effective, must be 

 applied in the spring and early summer, and some form of insoluble 

 sulphur should be used. We have experimented with a large number 

 of sulphur compounds, and the best among them is the iron sulphide 

 spray, now recommended. Three or four sprayings are required, but 

 fortunately these fit very nicely into the codling moth schedule, so that 

 only a small additional cost is entailed. The Bordeaux mixture is not 

 effective. 



The apple scab is another fungus disease which may prove serious if 

 there is much rain during April and May, but dry springs reduce the 

 damage to a minimum. This fungus grows within the tissues of the 

 leaves and fruit, and forms spores on the surface which resemble a 

 dark brown powder or .soot. The spores are carried by the wind, and 

 when deposited on apple foliage or fruit will start a new infection if 

 sufficient moisture is present. The injury consists in the scabbing of 



