12 CIRCULAR 867, U. S. DEPARTMENT OF AGRICULTURE 



set of fruit. Self -unfruitful varieties, such as Winesap and Delicious, 

 with favorable weather during the bloom period normally set heavily 

 at least three tree spaces away from a pollinating variety, provided 

 there are adequate bees or other pollinating insects. Under cool, 

 rainy, or windy conditions pollination may become a limiting factor 

 when these varieties are located more than one tree space from a 

 pollinizer. In fruit sections where such varieties are adapted for 

 chemical thinning it would seem advisable, for greatest safety in 

 seasons of adverse weather, to apply thinning sprays only if adjacent 

 to pollinizers, or at the most two tree spaces distant. 



Weather Conditions During Blossoming Period 



In the preceding discussion frequent reference has been made to 

 weather conditions as they are related to various factors influencing 

 the effectiveness of dinitro sprays. During the past several years it 

 has become increasingly evident that weather conditions existing 

 during the bloom period are perhaps the most important factors in 

 the success of thinning sprays. 



Working with Elgetol sprays in West Virginia in 1943 and 1944, 

 Batjer, Moon, and Kinman (.£), obtained results that were in decided 

 contrast during the 2 years. The weather in the 1943 bloom period 

 was cool and windy (mean minimum 43° F. ; mean maximum 69°), 

 with frequent showers. The weather the following year was much 

 warmer (mean minimum 54°; mean maximum 78°) and relatively 

 dry. In 1943 the application of Elgetol sprays on York Imperial 

 and Grimes Golden seriously overthinned, principally because fruit 

 set on unsprayed trees during that year was less than one-half that 

 which occurred in the more favorable year (1944). 



Dinitro sprays in the ^Northwest are more likely to thin heavily 

 during a cool, humid bloom period (as in 1948), even though a heavy 



Table 5. — Effectiveness of Elgetol thinning sprays at Wenatchee, 

 Wash., during 2 years of ividely different weather 1 





Fruits per 100 blossoming spurs in — 



Orchard and variety 



1947 



1948 





Unsprayed 



Sprayed 



Unsprayed 



Sprayed 



Birchmount orchard: 



Winesap 



Bond orchard: 

 Delicious 



Number 



54 



65 

 70 

 95 



50 



Xumber 



40 



50 

 52 

 70 



35 



Number 



50 



66 

 75 

 90 



23 



Number 



25 



35 



Winesap 



30 



Golden Delicious 



Ox Team orchard: 



Winesap. . _' 



45 

 3 



l During a 7-day bloom period at Wenatchee, W T ash., in 1947 and 1948, there 

 vere 108 decree-hours and 65 degree-hours (daily average), respectively, above 

 >0° F. 



