B levels were similar 

 each year for an annual 

 treatment, it appears 

 that any beneficial ef- 

 fect on Ca from high 

 rates of B application is 

 dependent on environ- 

 mental conditions in a 

 given year, and cannot 

 be depended upon. 



It is widely recog- 

 nized that when B con- 

 centrations in apples 

 are too high, early rip- 

 ening is promoted. By 

 chance, the block of 

 trees we chose for this 

 experiment contained 

 relatively high B levels 

 without any treatment. 

 Leaf B levels of 35 to 50 ppm are considered to be 

 optimum, and the lowest level measured in this ex- 

 periment was 42 ppm (Table 2). All treatments 

 except the 1/2 lb Solubor sprays raised levels above 

 the optimum range. Thus, it is important to observe 

 the effects of these treatments on fruit quality. 



In 1987, heavy premature fruit drop occurred 

 from many trees, and measurements of fruit remain- 

 ing on the trees indicated that the soil borate treat- 

 ments had accelerated fruit ripening. In 1988, fruit 

 were systematically sampled, and all B treatments 

 resulted in higher starch disappearance scores 

 (riper fruit) than in the treatment that received no B 

 that year (Table 4). These results were confirmed in 

 1989, and data from ethylene measurements were 

 consistent with those from the starch assessments 

 (data not shown). Therefore, our results showed 

 that when leaf B was raised above the optimum level, 

 fruit ripening was accelerated. 



Curiously, despite the accelerated ripening, 

 these high-B fruit were firmer than ones whose B 

 was within the optimum range (Table 4). This was 

 evident both at harvest and after storage for 4 

 months in 32°F air. These results were confirmed in 

 1989 (data not shown). This has been reported 

 before, although the reason for the greater firmness 

 is not known. While the greater firmness is certainly 

 desirable, the premature drop due to accelerated 

 fruit ripening precludes any thought of deliberately 

 overdosing with B to improve fruit firmness. 



The results of this experiment indicate that our 

 recommendation that a soil application of borate or 

 borax be applied every third year is not adequate 

 protection against B deficiency in apples, and that 

 the recommendations for 1/2 lb of Solubor per 100 

 gallons of spray is not equivalent to a soil B treat- 



ment. 



These results also show the importance of know- 

 ing the B status of apple trees through annual leaf 

 analyses . If trees have optimum B levels, then 

 premature fruit drop (along with a waste of money) 

 can be caused by application of an unneeded B 

 treatment. However, if trees are deficient in B — as 

 thev often are in the Northeast — then annual B 

 applications are needed to ensure strong tree growth 

 and good fruit quality. 



It appears that the recommendations for B treat- 

 ments to apple trees that are being made by Dr. 

 Warren Stiles at Cornell University are more appro- 

 priate than the ones that we have been making. 

 Therefore, his recommendations are presented as 

 follows. 



Very low leaf boron (less than 25 ppm). Apply 2 

 to 3 lbs of actual B per acre to the soil, plus , apply 

 3 sprays of Solubor at 1 lb/100 gallons dilute 

 equivalent at tight cluster to pink/white bud; 

 again at 7 to 10 days after petal fall; and again at 

 25 to 30 days after petal fall. 



Low leaf boron (25 to 34 ppm). Apply 2 to 3 lbs 

 of actual B per acre to the soil, plus , apply 2 

 sprays of Solubor at 1 lb/100 gallons dilute 

 equivalent at tight cluster to pink/white bud, 

 and again between 10 and 30 days after petal 

 fall. 



Leaf boron in optimum range (35 to 50 ppm). 

 Continue present B program. 



High leaf B (greater than 50 ppm) . Discontinue 

 use of B for one year, and resample. Be alert for 

 premature drop or occurrence of storage disor- 

 ders due to early fruit ripening. 



12 



Fruit Notes, Spring, 1991 



