GardenLine | Fruit to Grow and Pick | Factors Affecting Fruit Tree Production

In some years, fruit trees, such as apples, plums, pears, cherries, and saskatoons, produce few or no fruit. Poor yields may occur, despite heavy flower production; in other cases, few if any flowers may be produced. There are several possible reasons for this problem; and these include the physiological condition of the tree, lack of pollination, weather conditions, and insect pests and diseases.

Physiological Factors

Most fruit trees common to Saskatchewan gardens bloom during early to late May. The buds that developed into these flowers were formed during the previous growing season. Conditions during the period of flower formation can therefore influence flowering and fruit production the following year. Factors that decrease the amount of carbohydrates stored in the tree decrease the number of flower buds initiated. These include early summer pruning, defoliation by insects, excessive use of high nitrogen fertilizers, too much water, high temperatures, or heavy fruit crop production.

Lack of Pollination

Lack of pollination leads to a lack of fertilization and seed formation and thus no stimulation of fruit set. Tree fruit pollen, being heavy and sticky, must be carried from flower to flower by bees. Bees work best in warm, dry, calm weather and are less active in cool, wet, windy weather, which limits pollination. The use of insecticides during blossoming can kill bees, thus preventing pollination; some pesticides can also be toxic to the delicate flower tissues and cause abortion and loss of potential fruit. Generally, apples, crab apples, pears, plums, apricots, cherry plums and bush cherries should be considered self-sterile, that is, they can be fertilized by their own pollen. Self-sterile fruit trees must have a source of pollen within 500 m. The pollen source must be a tree of the same species but of a different cultivar, and which blooms at about the same time. This is especially important for the various plums and cherry cultivars. Self-sterile trees that are not pollinated, or poorly pollinated, will not produce any fruit.

Weather

Weather conditions can markedly affect tree fruit production. High temperatures can decrease flower bud development. Winter thaws followed by cold weather can kill flower buds. Frost during blossoming can damage flowers, and cool temperatures can decrease the viability of the pollen. Excessive rainfall in late-summer and early fall followed by freezing temperatures can damage flower buds that have not developed adequate winter hardiness.

Pests and Diseases

Finally, a large variety of insect pests and diseases can affect fruit trees. Poor fruit production can result from the direct effects of insects and diseases on growing and mature fruit. Insects and diseases that attack leaves, shoots or roots indirectly affect fruit production by negatively affecting the nutrient status of the tree.

Generally, if trees are healthy and properly looked after, they are better able to withstand attacks from insects, diseases, and inclement weather conditions, thus providing for more consistent fruit yields.

Richard St. Pierre

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.