Improving Fruit Quality
Preventing Apple Fruit Russet
Fruit russet, rough tan to brown patches or streaks on the skin of apples, is a particularly common problem in Golden Delicious. It is typically caused by the presence of water on the fruit surface during the first 45 days of fruit development. High relative humidity, dew or rain, light frosts, and reaction to some pesticides may also cause russeting.
Multiple applications of gibberellic acid (GA4+7) during the 45-day period after bloom has been shown to reduce fruit russeting. Beginning at late bloom or petal fall, apply GA4+7 (ProVide) in four consecutive sprays every 7 to 10 days. Apply 10 to 13 oz per 100 gallons (15 to 20 ppm). Do not exceed 40 oz/acre of ProVide in a single season. Excessive water volumes can contribute to fruit russet. ProVide can be tank mixed with pesticides, but should not be mixed with spreader-stickers or nutrient sprays. Do not apply ProVide through the irrigation system.
Improving Fruit Shape
Promalin is a combination of benzyladenine and gibberellins (GA4+7) that can be used to increase fruit size and “typiness” (fruit length) of lobed apple varieties such as Delicious. Apply a single application of 1 to 2 pints per acre from early king bloom to early petal fall. Alternatively, a split application can be made with 0.5 to 1 pints per acre applied at the beginning of the king bloom period, followed by a second 0.5 to 1 pints per acre application when the remaining side blooms have opened. Do not exceed 2 pints per acre within a season.
Reports from Michigan and other eastern regions have shown a negative interaction between Promalin application and subsequent NAA thinning applications. However, this has not been as big of a problem in the West.