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Title: Preemergence Control of Black Cottonwood in Nursery Containers

item Altland, James

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2009
Publication Date: 3/1/2009
Citation: Altland, J.E. 2009. Preemergence Control of Black Cottonwood in Nursery Containers. Journal of Environmental Horticulture. 27(1):51–55.

Interpretive Summary: Several cottonwood species (Populus spp.) are native throughout the U.S. While cottonwood are essential to local ecosystems, they can also be a serious weed problem in nurseries. Commonly used preemergence herbicides can prevent establishment of these species in nursery containers. Flumioxazin provided the most effective preemergence control of black cottonwood across two experiments. Timing of herbicide application is important for obtaining effective control. Cottonwood species release seed in a narrow window of time between May and June in Oregon, and late spring in general throughout the rest of the U.S. After seed release, seed must germinate within 2 weeks before losing all viability. Herbicides that are applied more than one month prior to seed release will be less effective than applications made immediately prior to seed release. The author recommends applying preemergence herbicides to containers prone to cottonwood infestation, one to two weeks prior to seed release. Cottonwood trees can be observed for swelling catkins to accurately time applications. When precise timing is not feasible, and applications must be made more than 4 weeks before probable seed release, flumioxazin should be applied (per label instructions).

Technical Abstract: Two experiments were conducted to evaluate preemergence herbicides for control of black cottonwood (Populus trichocarpa) in nursery containers. In 2006, granular preemergence herbicides were applied to recently filled, weed-free containers in May just prior to seed release from mature cottonwood trees. Flumioxazin provided the most effective cottonwood control, although control with isoxaben + trifluralin, oxyfluorfen + oryzalin, and pendimethalin was also effective. In 2007, containers were filled February 15, and herbicides were applied to separate groups of containers on Feb. 22, March 14, April 16, and May 15. Containers were over-seeded with cottonwood for a 2 week period starting on May 16. Control with most herbicides improved as the date of application neared the date of seeding. Flumioxazin provided the most effective control throughout the experiment, but also improved as the date of application neared the time of seeding.