What to Do About Alternate Bearing in Apple Trees? A Full Guide to Prevention and Treatment

Apples are sweet and tart, with thick flesh and plenty of juice, and different varieties differ in flavor; for instance, Granny Smith apples are fairly tart and crisp, while Red Fuji apples are fairly sweet. Recently, apple tree growers have asked, what should be done about alternate bearing in apple trees? Let us learn about the solutions.

I. Causes of alternate bearing in apple trees

The main cause of alternate bearing in apple fruiting is a disturbance in the tree's nutrient metabolism. Under different regional conditions, the physiological differentiation period of flower buds is the same, that is, before the 5th week after short shoots stop growing is the concentrated period of physiological differentiation, and after 5 weeks they enter morphological differentiation. The physiological differentiation period of apple flower buds happens to fall during the apple's swelling period, when the fruit tree needs a large amount of nutrients to supply fruit swelling. If there is too much fruit, the nutrients the tree supplies for flower bud differentiation will inevitably be reduced, causing insufficient flower bud differentiation. In an on-year, there is too much fruit, which consumes a large amount of the tree's nutrients; the tree's nutrients are insufficient, so fewer flower buds differentiate, and naturally fewer flowers bloom and fruit set the following year.

Improper pruning that makes the tree too vigorous will also consume a large amount of nutrients. Insufficient fertilizer application, soil compaction, poor root respiration, and poor ability of roots to absorb fertilizer and water will all cause nutrient deficiency, affect the growth of the fruit tree, and cause a large amount of flower and fruit drop. When pests and diseases occur severely, if the leaves are damaged, the fruit tree cannot produce sufficient photosynthetic products for fruit growth; if the root system is damaged, the supply of water and mineral elements cannot be guaranteed, resulting in an off-year. Next is abnormal environmental conditions: under severe climatic conditions, flower buds are frozen, and there are late frosts during the flowering period, plus the impact of heavy snow, strong winds, and heavy fog, so pollination and fertilization of flowers cannot proceed normally; low temperatures and strong winds during the young fruit stage cause a large number of young fruits to drop, and a sharp reduction in yield that year makes it an off-year. If the flower bud differentiation period is too dry, leaf wilting is unfavorable for flower formation. In addition, severe hail disasters and waterlogging disasters can all cause alternate bearing.

II. What should be done about alternate bearing in apple trees?

For on-year trees, on the premise of ensuring the yield of the current year, appropriately control the number of flowers and fruits to save nutrient consumption, promote flower bud formation, and lay the foundation for a high yield in the off-year;

For off-year trees, flower buds should be retained as much as possible to increase the fruit-setting rate and enlarge fruit size, so that the off-year is not small.

In fertilizer and water management, on-year trees should be topdressed with nitrogen fertilizer after flowering, and an appropriate amount of phosphorus and potassium fertilizer should be mixed in when applying base fertilizer;

For off-year trees, apply quick-acting nitrogen before germination and one week after flowering, and spray 1%—3% superphosphate after flowering.

Winter irrigation and irrigation before germination should be strengthened. On-year trees should control the number of flower buds; for off-year trees, all fruit branches should be retained, and vegetative branches should be properly headed back more heavily and left unpruned less; weak trees and weak branches should be strengthened by renewal pruning.

Thinning flowers and fruits not only has an obvious effect on overcoming alternate bearing, but can also enlarge fruit size, improve quality, and prevent premature aging of the tree. In addition, for off-year trees, artificial pollination and boron spraying during the flowering period should be strengthened to increase the fruit-setting rate.