A Test of a Potential Non-chemical 

 Approach to Scald Control on Apples 



William J. Bramlage 



Department of Plant & Soil Sciences, University of Massachusetts 



James R. Schupp 



Highmoor Farm, University of Maine, Monmouth ME 04259 



Scald Development on Apples 

 After Storage is a Threat 



There is risk of scald development during and 

 following long-term storage on a number of important 

 apple cultivars. Since the 1960's this risk has been 

 minimized by prestorage application of diphenylamine 

 (DPA), an antioxidant that has proven to be very 

 effective in scald control. Today, however, some 

 markets will not accept DPA-treated apples because 

 they have been treated chemically, so alternatives to 

 DPA are being sought. 



Numerous non-chemical scald-control procedures 

 have been proposed, but none are as easy to apply or as 

 reliable as the use of DPA. The most effective probably 

 is low-oxygen controlled atmosphere storage, where O^ 

 iskeptnearorbelow 1%. Itisusedforcommercial scald 

 control in some parts of the worid; however, in the 

 Northeast we are unable to use low-Oj storage because 

 the risk of fruit fermentation is excessive. 



One non-chemical procedure that has been tested is 

 warming of fruit after a short time at low temperature. 

 In New Zealand, Dr. Chris Watkins and I found that 

 when Granny Smith apples were warmed at 70°F for 

 five days after they had been at 32°F for two weeks, 

 warming was as effective as DPA in preventing scald 

 development. Subsequent tests indicated that this 

 warming time and temperature was about optimum for 

 scald control on Granny Smiths. In 1992, we tested this 

 warming procedure on Cortland and Delicious in Mas- 

 sachusetts, and found that it caused significant fruit 

 ripening and gave little or no scald control. However, 

 we had used fruit that were immature and extremely 

 scald susceptible, so the treatment might have given 

 better results if the fruit become less scald susceptible. 

 It is likely that as fruit become less scald suscep- 



tible, scald becomes easier to control. We found several 

 years ago that as Cortland and Delicious become less 

 scald susceptible, lower concentrations of DPA become 

 effective in controlling scald. It is our hypothesis that 

 at lower levels of scald susceptibility, non-chemical 

 control measures may be as effective as DPA. The 

 problem is how to determine at harvest when fruit have 

 relatively low scald susceptibility. However, we have 

 found that in Massachusetts, preharvest hours below 

 50°F is a reasonably reliable indicator of scald suscep- 

 tibility on Cortland and Delicious (see Fruit Notes 

 59(3):6-10). Therefore, it is conceivable that by moni- 

 toring preharvest temperature, a grower could know 

 when DPA is necessary for scald control, and when a 

 non-chemical procedure might be used instead. 



Experimental Procedures 



In 1993, the Maine State Pomological Society 

 provided funding for a test of this concept. Fruit for the 

 study were provided from the University of Maine's 

 Highmoor Farm, and treatments, storage, and fruit 

 evaluations were done at the University of Massachu- 

 setts Horticultural Research Center (HRC). 



Three cultivars were tested: Mcintosh, Cortland, 

 and Delicious. Fruit were harvested from the same trees 

 when 75 , 1 1 9, 1 50. and 200 hours below 50°F had been 

 recorded at Highmoor Farm. Harvest dates were Sep- 

 tember 20 and 27 and October 1 and 5. All three 

 cultivars were harvested on these dates. Maturity was 

 assessed by using a starch test within one day of harvest, 

 and by measuring ground color and firmness after 

 transport to the HRC. Within a week of harvest, one set 

 of one-bushel samples of each cultivar was dipped for 

 two minutes in DPA (1000 ppm for Mcintosh, 2000 

 ppm for Cortland and Delicious). After two weeks at 



Fruit Notes, Fall, 1994 



