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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Fruit Drop and Hand Thinning

This article was published originally on 5/19/1995
Gardeners are often surprised when small apples and other fruit drop prematurely to the ground. However, premature fruit drop is relatively common on apples and other fruit trees. The home gardener shouldn't be alarmed if the fruit tree appears healthy. The fruit drop may simply be nature's way of reducing a heavy fruit load.

Two fruit drop periods commonly occur on apples. The "first drop" occurs shortly after petal-fall and may continue for 2 to 3 weeks. The fruit that falls during this period is pea-size and may be the result of poor pollination. Most apple varieties are considered self-unfruitful. These fruit varieties will produce little or no fruit when pollinated with their own pollen. Another variety (cultivar) is required for cross-pollination and fruit set. 'Jonathan' and 'Yellow Delicious' are two apple varieties which are notable exceptions. Each will produce a fairly good crop without cross-pollination. A lack of pollination may also be due to poor weather. Most fruit trees are pollinated by bees. They are most active on sunny, warm days. There is little bee activity during cool, rainy weather. Cool, rainy weather during the bloom period reduces bee activity, results in poor pollination, and may lead to fruit drop. Exposure to freezing temperatures during flower bud development and bloom may also cause fruit drop.

The "second drop" usually occurs in early June. (This is commonly referred to as "June drop.") The fallen apples are approximately 1/2 to 1 inch in diameter. The second shedding of fruit is often due to the competition among the developing fruit for food, water, and nutrients. This natural thinning removes excess fruit and allows the remaining fruit to develop properly. Hot, dry weather in late spring will contribute to fruit drop.

While the number of fruit which fall to the ground as a result of natural thinning may seem quite high, additional thinning may be necessary. Trees overloaded with fruit need additional thinning to (1) obtain large, high quality fruit at harvest; (2) allow development of flower buds for next year's crop, thus overcoming the tendency for some fruit trees to bear fruit in alternate years; and (3) prevent limb breakage. Hand thinning of apples should be done within 6 weeks of full bloom. Leave the largest apple in a cluster unless it is damaged. After thinning, the apples should be spaced about 8 to 10 inches apart on the branch. Pears, plums, and apricots may also require hand thinning. Fruit should be spaced about 6 to 8 inches apart on the branches following thinning.



This article originally appeared in the May 19, 1995 issue, p. 69.

Year of Publication: 
1995
Issue: 
IC-470(12) -- May 19, 1995