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When calcium level is low in apples, they are much more susceptible to bitter pit and postharvest senescent breakdown. Most fruit calcium accumulates early in the season, but absorption of calcium by roots is greatly reduced by dry soil conditions. The dry weather conditions throughout orchards this year very likely have lowered fruit calcium levels, increasing the opportunity for bitter pit and senescent breakdown development. Even if we get substantial rain between now and harvest, the situation probably will not improve. In fact, it would probably be worsened, because increased fruit size would further dilute what calcium is in the fruit.
Growers are encouraged to apply as much foliar calcium as is feasible between now and harvest. We recommend 2.7 to 3.3 lbs of calcium chloride (77-80% Ca) per 100 gal dilute at this time of the season, every 2 weeks. However, calcium chloride should not be applied in hot weather (85oF or higher) because of increased risk of injury to leaves. Calcium nitrate carries less risk of foliar damage, but it needs to be applied at 4.3 to 5.3 lbs per 100 gal dilute to obtain equal benefit.
Further information is available from Cooperative Extension Leaflet L-553.
Southern New England continues to experience the hot dry conditions that plague many portions of the east. Fruit growth rate has been slowed. Fruit diameter in monitored blocks of McIntosh, Delicious, and Gala were : 2.25 in., 2.42 in., and 2.50 in., respectively. This represents approximately a 30% reduction in growth rate compared with growth rates under nonstressed conditions. Fruit maturity has been advanced by the stress associated with these conditions. Maturity has been advance from a few days to over a week depending upon soil type and the occurrence of isolated thunderstorms. ReTain should be applied to McIntosh and Gala within the next 10 days. It is not too early to consider applying ReTain this week. Since ReTain is somewhat forgiving with respect to time of application, choose a day to make the application that assures good spray coverage and the threat of washoff due to rain is low. The full rate of ReTain is recommended on all McIntosh. A full rate of ReTain on Gala may delay maturity by as much as 3 or 4 weeks. If a delay in maturity of this magnitude is undesirable, we suggest that you apply a half rate or a reduced rate on this cultivar.
The failure of ReTain to reduce preharvest drops in the past has been associated with stressful conditions caused by drought, excessive heat, or foliage damage caused by insects or disease. The use of ReTain in severely stressed blocks should be weighed against the possibility of reduced preharvest drop efficacy under these difficult conditions.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Duane Greene except where other contributors are noted. Edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
