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Title: Weed Growth and Efficacy of Pre-Applied Herbicides in Alternative Rooting Substrates Used in Container-Grown Nursery Crops

item WEHTJE, GLENN - Auburn University
item Altland, James
item GILLIAM, CHARLES - Auburn University
item MARBLE, STEPHEN - Auburn University
item VAN HOOGMOED, ALBERT - Auburn University
item FAIN, GLENN - Auburn University

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2009
Publication Date: 8/1/2009
Citation: Wehtje, G., Altland, J.E., Gilliam, C.H., Marble, S.C., Van Hoogmoed, A.J., Fain, G.B. 2009. Weed Growth and Efficacy of Pre-Applied Herbicides in Alternative Rooting Substrates Used in Container-Grown Nursery Crops. Weed Technology. 23:455-459.

Interpretive Summary: As the price of pine bark increases, and its availability decreases, alternative substrates are being explored. Several new substrates include materials that are composed of pine bark, wood, and needles, as opposed to just the bark fraction. Weed growth in response to herbicide application is well documented and understood in pine bark substrates. Changes in the composition of the substrate could alter herbicide effectiveness. The goal of this research was to determine if weed growth in alternative substrates was similar to traditional pine bark substrates in response to herbicide rate. Our research studied three common weed species in response to three common nursery herbicides. In each case, weed control was similar or better in alternative substrates compared to pine bark substrates. We conclude that nursery weed management programs would not change when adopting the alternative pine wood based substrates used in this experiment. These results will impact all nursery growers who desire to switch from traditional pine bark substrates to alternative substrates comprised of pine wood, needles, and bark.

Technical Abstract: Container-grown nursery crops in the Southeastern United States are typically grown in a rooting substrate comprised primarily of the ground bark of pine trees. However pine bark is becoming less available and more costly due to changes in production and marketed practices within Southeastern pine forestry. This shortage has resulted in the economic incentive to seek pine bark alternatives. Two possible alternatives are ‘clean chip residual’ and ‘whole tree’. These alternatives are like pine bark since both are products of southern pine forestry. Unlike pine bark which is a single part of the tree, these alternatives contain all parts of the tree including wood and foliage in various portions. Registration of preemergence-active herbicides has been based solely upon data obtained from pine bark-based nursery production. Research was conducted to determine if the control of 1)large crabgrass with prodiamine, 2)eclipta with flumioxazin, and 3) spotted spurge with isoxaben would be comparable in these alternatives to what has been established in pine bark. Seed germination of all three weed species in no-herbicide controls was approximately 10% and equivalent between pine bark and the alternatives. Foliage fresh weight production of large crabgrass and spotted spurge was less in the alternatives compared to pine bark; eclipta was not affected. For all three weed species-herbicide combinations, weed control was nearly identical between pine bark and the alternative substrates provided the herbicide had been applied at its registered rate. For all three herbicides, rates that are effective in pine bark substrates will be equally effective in the pine bark alternatives.