-22- 



Use of chemical thinning following Promalin application. Promalin applied by itself is 

 capable of thinning. A chemical thinner, generally Sevin, is often used during the 

 post-bloom period on Delicious. Frequently, increased thinning is observed when 2 

 different thinning agents are applied. Therefore, it is particularly important to know 

 if Promalin-treated trees are thinned to a greater extent than unsprayed trees when 

 chemical thinners are applied. We have attempted to answer this question with 5 different 

 experiments over the past 4 years using both Sevin and NAA as chemical thinners. Results 

 of a typical experiment are shown in Table 3. When applied as a dilute spray during the 

 bloom period, Promalin thinned. Sevin thinned Promalin-treated or untreated trees 

 comparably. In no experiment did the combination of Promalin with either chemical 

 thinner reduce the crop load below that on trees treated with either Promalin or the 

 chemical thinner alone. Very 'typey' fruit with large L/D ratios were harvested from 

 both Promalin and Promalin-plus-chemical thinner trees. 



Table 3. Effect of Promalin, Sevin, and naphthaleneticetic acid (NAA) on fruit set, fruit characteristics anc 

 yield of Double Red Delicious apples. 

 1982. 



^Promalin applied 5/12/82 (full bloom 5/13/82) as a dilute spray with 1 pt/100 gal. Glyodin. Sevin and NAA 

 applied as a dilute spray on 5/30/82. 



Weather conditions following chemical thinner application were cloudy and moist 

 thus favoring foliar penetration. Complete drying of spray droplets did not occur for 

 24 hours. Trees treated with NAA soon showed typical leaf epinasty (twisting) and the 

 development and retention of many small and seedless 'pygmy' fruit became apparent. 

 It is for this reason that NAA appears not to have thinned and that average fruit size 

 on these trees was considerably smaller (Table 3). Although 'pygmy' fruit were observed 

 only one year, this illustrates the potential danger of using NAA as a chemical thinner 

 for Delicious. 



It should be noted that Promalin did not increase fruit weight (Table 3). We have 

 never observed an increase in fruit size following Promalin application unless the treatment 

 caused significant thinning. The increase in fruit length caused by Promalin was 

 accompanied by a corresponding reduction in fruit diameter. The reduced fruit diameter 

 is attributed to a reduction in seed number. 



