Preventing Unwanted Fruit - Marion County
Preventing Unwanted Fruit on Ornamental Trees and Shrubs
By Steve Mayer
Extension Educator-Horticulture
Purdue Extension-Marion County
The fruit on some ornamental trees adds color and interest to the landscape. However, the fruit or seeds of other trees can be a maintenance problem. The tree mentioned most often is the sweetgum with its spiked seed balls. Sometimes the seed balls are so numerous they are messy and even hazardous. However, there is something you can do about the problem.
The ideal way to prevent unwanted fruit is to select trees and shrubs without objectionable fruit. Fruitless varieties are available on some plants. For example, to avoid the messy, stinky fruit of ginkgo trees, choose a named male cultivar (cultivated variety).
There is a fruitless sweetgum ('Rotundiloba') with rounded lobes on the leaves but it has winterkilled at temperatures below -10 degrees F. This makes it too tender for central Indiana except in special microclimates. In addition, individual branches occasionally revert to the typical sweetgum star-shaped leaves with fruit.
Another way to prevent objectionable fruit is to physically remove the developing fruit after flowering. However, this is not practical for large trees or extensive shrub plantings.
Products containing plant growth regulators are another option to prevent unwanted fruit. However, they do not work on all plants, and they may work to varying degrees depending on the weather, specific plant cultivar as well as how and when they are applied. Plant damage could also occur if the products are not applied carefully.
The most common "fruit eliminator" products contain the active ingredient ethephon. This plant growth regulator releases ethylene, a naturally occurring plant hormone, causing fruit to drop in its earliest stages before it sets.
Limited research is available on the effectiveness of specific plants. Kansas State researchers near Wichita got mixed results when treating crabapples. With some varieties, fruit was substantially thinned. Others showed no effect. Generally, fruit elimination may not be satisfactory on small, red fruited varieties of crabapples. The specific product label information may help you decide if fruit elimination treatments are right for you.
According to the label, a foliar spray will reduce or eliminate undesirable fruit development on many ornamental trees and shrubs such as: apple, carob, cottonwood, crabapple, elm, flowering pear, horsechestnut (buckeye), maple, oak, olive, pine, sour orange, sweetgum and sycamore. There is no evidence of effectiveness on other trees not listed.
Fruit eliminator products must be used each year in order to work. Spray the entire plant to sufficiently wet the flowers and foliage, but do not allow runoff to avoid plant injury. Inadequate coverage may cause incomplete fruit elimination. Ethephon degrades quickly in water so applications should be completed within four hours of mixing.
Because ethylene production within the plant is stimulated by stress, do not treat plants under stress from drought, high temperature, disease or other environmental stress conditions. Treating stressed plants may result in leaf scorching or defoliation.
The weather plays a role in effectiveness. Ethephon is slower to act when temperatures are low (60 degrees F) or very high (95 degrees F).
Apply ethephon products prior to fruit set at the mid to full bloom stage of the particular plant. This will require close observation. Sprays applied too early or too late will be less effective and result in incomplete fruit elimination. Sweetgum blooms appear about the time the redbud trees are flowering. Wait until the round female sweetgum flowers are present before treating.
The photos show sweetgum and redbud trees in full bloom on the same site in Indianapolis on April 23, 2003. They also bloomed together the following year (April 21, 2004).
All photos taken by Steve Mayer, Purdue Extension-Marion County, Indianapolis, Indiana
March 2005
