Efficacy of preemergence herbicides over time

Authors: Altland, James

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2019
Publication Date: 6/1/2019
Citation: Altland, J.E. 2019. Efficacy of preemergence herbicides over time. Journal of Environmental Horticulture. 37(2):55-62.

Interpretive Summary: There are numerous preemergence herbicide products available for container-grown nursery crops. It has been established that some herbicide active ingredients are more effective at controlling certain weeds than others. This information is used by growers in develop weed management programs. Another factor affecting herbicide performance is how long the product will remain effective on the substrate surface. There is comparatively less information on herbicide longevity. The objective of this research was to provide more information on how long several commonly used herbicides remain effective after application. Herbicides containing oxyfluorfen or flumioxazin provided effective preemergence bittercress and creeping woodsorrel control even when weed seeds were introduced to the containers up to 8 to 10 weeks after herbicide application. Other herbicide products, including pendimethalin or prodiamine + isoxaben resulted in reduced control as the time between herbicide and seed application increased. This information provides growers with additional criteria to develop effective weed management programs.

Technical Abstract: Preemergence herbicides are applied to container-grown nursery crops repeatedly throughout the year, often in 8 to 10 week intervals. Preemergence herbicide efficacy may decline over time, resulting in reduced weed control several weeks after application if seed pressure remains high. The objective of this research is to evaluate efficacy of preemergence herbicides on creeping woodsorrel (Oxalis corniculata L.) and flexuous bittercress (Cardamine flexuosa With.) by applying weed seed from 0 to 10 weeks after herbicide application. Pendimethalin, prodiamine + isoxaben, oxyfluorfen + pendimethalin, and flumioxazin were applied at their maximum labeled rates to separate groups of containers every two weeks for ten weeks. After the herbicide application at 10 weeks, 40 seeds of creeping woodsorrel and flexuous bittercress each were applied to all containers. All herbicides provided effective control when seed were applied within 2 weeks of herbicide application. Herbicides containing oxyfluorfen or flumioxazin provided effective preemergence bittercress and creeping woodsorrel control when seed were applied up to 8 to 10 weeks after herbicide application. Other herbicide products resulted in reduced control as the time between herbicide and seed application increased.