-21- 



Table 2. The effects of surfactants and pH modification on the performance of 

 Promalin applied to Royal Red Delicious, 1978. 



^l pt of each chemical was used per 100 gal. of water. Treatments applied at 

 rate of 125 gal/acre at petal fall of the king blossom. 



yNumbers in a column followed by different letters are significantly different at 

 odds of 19 to 1. 



Fruit set following Promalin application. Within 2-3 days following a Promalin appli- 

 cation, calyx swelling and closing is apparent, first on the king blossom and then on 

 lateral blossoms. Promalin merely accelerates that which normally occurs on pollinated 

 flowers. Ten to 12 days after application, Promalin appears to have increased fruit 

 set. However, about 15 days after bloom, yellowing of the pedicels occurs on many 

 of the developing fruit in the cluster. By 3 weeks after bloom most of the less vigorous 

 fruit have dropped and within 4 weeks after bloom fruit set has been determined and 

 subsequent drop is minimal. 



Thinning due to Promalin application. It is well documented that Promalin can thin. 

 However, in most cases where Promalin has thinned, label directions were not followed. 

 Causes of thinning include: 



1. Overapplication. The most frequent cause of thinning due to over-application is 

 poor sprayer calibration. Portions of a tree also may be overthinned due to poor 

 spray distribution within the tree. Lower, weaker spurs thin more easily than more 

 vigorous spurs located in the tops of trees. 



2. Application during hot weather. If Promalin is applied when temperatures exceed 

 85°F, the likelihood of thinning is dramatically increased. 



3. Application on young trees. Treatment of young trees frequently results in complete 

 removal of the crop. This is particularly detrimental on young Delicious trees just 

 coming into bearing since even a small crop is quite useful to bring down branches, 

 help slow growth and encourage consistent fruiting. 



Nevertheless, thinning due to Promalin may also be more apparent than real. Pro- 

 malin may merely accelerate young fruit abscission that would normally occur during 

 the early 'June-drop' period. It would certainly appear that Promalin was increasing 

 thinning if you assessed fruit set 2-3 weeks after bloom. However, in most situations, 

 it appears that Promalin has advanced the 'June-drop' by about 2-3 weeks, thus giving 

 only the impression of thinning. While Promalin can indeed cause thinning, caution 

 should be exercised in concluding that this has happened on your trees. 



