Issue: November 11, 2000

All apples fall from tree early

I have a Red Delicious apple tree in my yard. I am guessing that the tree is 30 years old or more, but no older than 40. We first moved into our house 10 years ago, and that year's crop of apples was full of worms but were very tasty and extremely large. Since that year, the apples bloom and I get a great fruit set; however, by midsummer the apples start to fall off the tree at a rate such that I have no crop to pick by the end of summer. Some of the apples even rot on the tree, so by the time they fall and hit the ground, they look like apple sauce.

Another consideration is the fact that after I moved to the house I took out the grass that was under the tree and put pea gravel around the tree and a majority of the surrounding area. The area is very shaded from other trees in the area which keeps the gravel cooler than if in the direct sunlight; however, it is now hotter than when the grass was there. What could be the problem and how could I correct it? Bill Kolb Artesia, NM

There are several things that could be contributing to the problem. One of them is the worms you mentioned. The fact that many of the apples rot while still on the tree suggests that the codling moth larvae (worms) are infesting them. Apples infested with codling moths will have rotten areas within the developing fruit and will often drop from the tree. The gravel under the tree may be a contributing factor by providing a place for the larvae to pupate and develop into moths which will lay eggs in the next year's crop. I conferred with Bob Cain, NMSU Extension Forest Entomologist, and Carol Sutherland, NMSU Extension Entomologist. Dr. Sutherland reported that codling moth infestations can cause 100 percent crop loss as you are describing. Both agreed that the gravel might create an increased problem by providing a safe place for the moth larvae to pupate. They also stated that the most common place for the larvae to pupate is on the branches and trunk.

It is important to remove fallen fruit (even small apples) as soon as they fall so that the codling moth larvae are removed from the vicinity of the tree. Failure to do so allows the codling moths to increase to harmful population levels near your tree. If you wish to compost the fallen apples, be certain that they are placed into a hot part of the compost pile where the larvae will be killed by the heat. Otherwise, they will pupate in the cool part of the compost pile and emerge as adult codling moths to lay eggs in your apple tree next year.

Treatment with an insecticide for codling moth management may be necessary. If you decide to use an insecticide, choose a product labeled for controlling codling moth in apple trees and carefully follow the directions.

It is important that you provide irrigation to the tree where the lawn was removed. The tree developed roots in the lawn area because there was water there to maintain the lawn. Although the pea gravel will serve as a mulch to reduce evaporation of water from the soil, irrigation will be necessary. Water well to moisten the soil to a depth of at least two-to-three feet every two weeks in the summer and once a month in the winter. Insufficient water can cause fruit drop.

Poor pollination due to a deficiency of pollinators (honey bees) could also be a part of your problem. Honey bee colonies have been greatly reduced by mite infestations. This would result in the loss of large numbers of small fruit early in the growing season.

Another factor may be the shade from nearby trees. Apple trees need several hours of direct sunlight each day. If the surrounding trees that are shading the gravel are also shading the tree, the competition for light could be causing the loss of fruit. In addition to competing with the apple tree for light, these trees are also competing for water and nutrients. Competition for light, water, and nutrients may be a more difficult problem to solve, especially if the other trees are on your neighbors' properties. More frequent irrigation should help if this is the problem.

Finally, there is a percentage of fruit that will drop in the summer every year. This is aggravated by competition from other trees and by the infestation by codling moths.

Send your gardening questions to Yard and Garden, ATTN: Dr. Curtis Smith NMSU Cooperative Extension Service 9301 Indian School Road, NE, Suite 112 Albuquerque, NM 87112

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.

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