-5- 



Terrainals pruned from Red Delicious trees in a block that had a little pow- 

 dery mildew last summer showed no mildew on the bark or on the buds when the 

 terminals were brought into the laboratory. When placed in water and forced, 

 the new leaves showed an abundance of powdery mildew threads and spores. It is 

 obvious that the powdery mildew in overwintering buds is alive and ready to in- 

 fect new growth early in the season as soon as conditions are favorable. 



To keep mildew from building up and becoming serious, it will be necessary" 

 to begin mildew control early, especially in orchards where there was even a 

 small amount of mildew last year. In orchards where there was no mildew last 

 year, prevention could be started in the early scab sprays, otherwise, control 

 should be started as soon as mildew is discovered. A small amount of sulfur, 

 one or two pounds, in the pre-cover scab sprays, with Karathane, 1/4 to 1/2 

 pound at 7 to 10 day intervals, in the cover sprays to about the 4th cover when 

 terminal growth slows down, keeps powdery mildew under satisfactory control. 

 On sulfur-sensitive varieties, such as Red Delicious, Baldwin and others, it is 

 advisable to change from sulfur to Karathane in Pink to reduce russetting. 

 Specific directions for various situations will be found on the inside cover of 

 the last page of the Apple Spray Charts for 1960. 



The following information about mildew will be helpful in controlling it: 



Unlike scab, mildew does not need free water for spore germination and in- 

 fection and, in fact, free water hinders and prevents spore germination. A 

 high relative humidity, over 90%, however, is necessary and such conditions do 

 exist on foggy, damp, and dewey nights. 



Infections occur at temperatures between 55 and 80° F. with best mycelial 

 growth and spore germination at about 70°F. Infections become visible in two 

 or three days. 



The best control is obtained with sprays applied regularly and thoroughly 

 so that the mildew is wet. For better wetting, some glyodin or wetting agent, 

 such as Triton B-1956 or Du Pont spreader-sticker, may be necessary. 



C. J. Gilgut 



I I I I I I I I I I I I I I I I 



CHEMICAL THINNING 



By this time I'm sure you have received word that all the common chemical 

 thinning (and preharvest drop control) materials for both, apples and peaches 

 have been cleared for use through 1960. VJhether these materials will have 

 clearance beyond 1960 from the Food and Drug Administration will depend in some 

 measure on work that is to be carried out during the 1960 growing season at 

 several experiment stations. 



Special Circular No. 189 on Chemical Thinning of Apples has been revised 



