Pest
Management Home Page Dr. John F. Baniecki Each year, homeowners apply fertilizers containing broadleaf weed killers on their lawns. These materials may be effective in controlling broadleaf weeds while fertilizing the lawn, but their use can result in injury to ornamental plants. Even when these materials are used according to manufacturer's recommendations, injury has been observed on many trees, shrubs, and flowers. Sick ornamentals sent to the laboratory show definite symptoms of herbicide damage. The injury appears as a twisting and gnarling of the new green stems, twisting and curling of the leaf petioles, and cupping and other distortions of the leaves. Severe injury to ornamental plants results from improper and careless use of these materials. Such practices as making double applications of fertilizers containing broadleaf weed killers near, under or around trees and shrubs will not only increase the concentration of fertilizers, but will also increase the amount of weed killer being applied to a given area. Symptoms of injury as a result of improper applications of these materials will often persist through one or more growing seasons. Repeated applications or constant use of these materials will weaken ornamental plants and make them more susceptible to extreme environmental conditions such as heat, cold and drought. Plants that are affected from the proper use of fertilizers containing broadleaf weed killers will generally recover within the first growing season and resume normal growth. There appears to be no permanent damage to ornamental trees and shrubs when only slight weed killer symptoms are observed. If fertilizers containing broadleaf weed killers must be used for the control of lawn weeds, they should be applied with extreme caution. When applying them to landscaped areas, allow a wide margin of safety around all ornamental plants. Roots of established trees and shrubs extend far beyond the drip line of their branches and fertilizers containing broadleaf weed killers applied within this area can be easily washed into the soil, absorbed by the feeding roots and translocated throughout the plant. Additional precautionary measurers must be taken when applying fertilizers containing broadleaf weed killer on sloping areas because they can easily be washed downhill by heavy rains. Therefore, an additional margin of safety should be allowed when applying these materials on sloping lawns bordering ornamental plantings. It is generally agreed that most weeds found in lawns can easily be controlled by such cultural practices as a good fertilizer program and by properly adjusting the cutting height of the lawnmower. Weed killers should only be used when persistent weeds cannot be controlled by cultural means. Once a broadleaf weed killer enters the plant, there is nothing that can be done that will stop its action. These materials are hormone-like in nature and become part of the plant sap. Because they are easily translocated throughout the plant, the symptoms are rather uniformly distributed. Plants showing symptoms of broadleaf week killer injury should be kept well watered at all times, especially during periods of drought. During the fall, winter or spring the plants should be fertilized with a complete fertilizer in order to restore plant vigor. |
