are made in the peel, and therefore these arc the 

 cells that are killed. 



Factors affecting scald . Different cultivars 

 vary greatly in scald susceptibility. For example, 

 Cortland is extremely susceptible and nearly was 

 abandoned until effective scald-control methods 

 were developed. On the other hand, Golden 

 Delicious has very low susceptibility. The huge 

 increase in production of Granny Smith worldwide 

 has intensified concern about scald, since this 

 cultivar is extremely scald susceptible. 



Susceptibility of a given cultivar is not 

 constant, however. It is widely recognized that 

 immature fruit tend to be more susceptible than 

 over mature ones. Although this relationship is 

 not invariably true, it is strong enough that 

 growers should be much more concerned about 

 scald on early-picked than on latc-pickcd fruit. 



Color is another important factor. Scald is 

 more likely to occur on a green area than on a 

 well-colored area of the fruit. This relationship 

 is probably indirect; good exposure to sun is 

 probably what reduces scald susceptibility, rather 

 than red pigments. Thus, the production of red 

 strains of susceptible cultivars largely obscures 

 the fact that shaded areas and shaded fruit are 

 more susceptible than exposed areas and exposed 

 fruit. Excessive tree vigor and inadequate 



pruning (hence, fruit shading) probably increase 

 scald susceptibility, while summer pruning 

 probably decreases it. 



Scald susceptibility varies considerably from 

 year to year for a given cultivar. To a large 

 extent this variability is the result of the 

 influence of weather on scald susceptibility. 

 Studies in England (2) showed that weather 

 conditions from late July to the beginning of 

 September were very important: hot, dry weather 

 increased scald susceptibility; cool, damp weather 

 decreased it. Indications were that water stress 

 may have been more important than temperature 

 in this relationship. Studies in New Jersey (3) 

 showed that hot weather shortly before harvest 

 increased scald susceptibility; when Stayman 

 Winesap apples had experienced 190 or more hours 

 of temperatures below 50"F they did not develop 

 scald, but as this total dropped scald 

 susceptibility increased. Thus, a cool moist 

 August and a cool harvest season should greatly 

 reduce scald susceptibility; whereas, a hot dry 



August and a hot September should increase it. 

 How these two periods interact is not clear. 

 For example, 1987 had a hot dry August but a 

 cool September. Is one of these situations more 

 important than the other? 



Control measures . Numerous approaches to 

 controlling scald have been developed, since 

 losses to the disorder can be devastating. Early 

 approaches recognized that scald was caused by 

 a volatile compound and were aimed at 

 maximizing evaporation of the compound from 

 the fruit during storage. These techniques 

 included use of air purifiers in the storage, 

 storage ventilation, and paper wraps that were 

 impregnated with mineral oil. These techniques 

 reduced the amounts of scald that developed, but 

 did not control it. 



CA storage greatly reduces scald. Both low 

 O2 and high CO2 can be effective. However, 

 since CO2 is most effective at concentrations 

 above 5% and most cultivars are susceptible to 

 CO2 injury above 5%, for most cultivars the 

 greatest benefit from CA is from the low O2. 

 The low O2 impedes oxidation of alpha farncsene 

 to conjugated trienes, the toxic materials. This 

 effect is much greater at 1 to 2% O2 than at 3% 

 O2, and many researchers have shown that scald 

 can be nearly completely controlled at 1 to 1.5% 

 O2. However, in the Northeast we have 

 generally been unable to store fruit at less than 

 3% O2, so we are unable to take full advantage 

 of the scald control from CA. At our 

 recommended CA conditions, scald is still a 

 potential problem. 



An important factor in scald control 

 through CA is rapidity with which CA conditions 

 are established. Delayed sealing or slow 



generation of an atmosphere can greatly increase 

 the risk of scald development after storage. 

 Rapid CA is an excellent scald control measure, 

 especially where O2 cannot be reduced below 3%. 



Ethylene-scrubbing during CA storage can 

 also control scald. In England, scald virtually 

 was eliminated from fruit taken from a 

 commercial ethylene-scrubbed storage (1). 

 However, the feasibility of ethylene scrubbing in 

 commercial storage for most cultivars is doubtful, 

 so this method seems to have limited application. 



The most reliable scald-control measure is 



