Conservation Buffers and Ecological Weed Management in Southeast Organic Cropping Systems : Weed Seedbanks and Weed Seed Predators

FOX, AARON FREEMAN. Conservation Buffers and Ecological Weed Management in Southeast Organic Cropping Systems: Weed Seedbanks and Weed Seed Predators. (Under the direction of Dr. S. Chris Reberg-Horton and Dr. David Orr). Conservation buffers, areas of non-crop vegetation integrated into agricultural landscapes, enhance many agroecosystem services. Among other benefits, these buffers provide habitat for wildlife and beneficial organisms such as pollinators and pest enemies. However, non-crop vegetation in agricultural settings can also be a source for crop pests. One buffer strategy, fallowing strips of land adjacent to crop fields, provides critical habitat for threatened wildlife species, but fallow strips may increase in-field weeds by creating a reservoir of weed seeds that spreads into the adjacent crop. Fallow buffers also offer few resources for beneficial organisms that provide important pest management services. It has been suggested that conservation buffer practitioners move away from fallowing towards plantings of native forbs and grasses. Planted buffers provide more resources for beneficial organisms while maintaining good habitat conditions for wildlife. It is not clear, however, how these planted buffers augment or diminish weed dynamics in the agricultural landscape. Ecological weed management, an integration of many indirect weed management strategies, can be of critical importance to organic growers who are restricted from using conventional weed management tools. The first two studies of this dissertation examined multiple field edge strategies to determine if they have an impact on ecological weed management in organic cropping systems. The first study investigated how the bank of weed seeds in the soil (the ‘weed seedbank’) changed over time in relation to field buffer management, distance away from the field edge, and crop type. Results showed how planted buffers, especially those with native warm season grasses, can reduce the number of weed seeds that enter the seedbank. The second study examines how ground dwelling, seed eating organisms (‘weed seed predators’) to the different field buffer management schemes. The results from this study showed that field buffers had little to no influence on weed seed predators or on the seed predation services they provide. However, crop type did heavily influence these organisms as well as seed removal. Fields with crops that provide dense cover, such as hay, experienced more weed seed predation than fields that were more open and had less vegetative cover, such as harvested maize fields. The results from this weed seed predation experiment, however, may reflect conditions that are specific to our system and to the southeastern United States. One important aspect of the Southeast in relation to weed seed predators is the recent introduction of the invasive red imported fire ant, Solenopsis invicta. Although this ant is now present in high numbers inside southeastern U.S. agricultural fields, it is not clear if they are contributing to weed seed predation services. The third study of this dissertation used video monitoring in an agricultural field to collect direct evidence of Solenopsis invicta and their impact on summer annual weeds. The video data suggest that this ant is not contributing to weed seed predation services. It is not clear from the video data, however, what impact these invasive ants have on native weed seed predators. © Copyright 2013 by Aaron Freeman Fox All Rights Reserved Conservation Buffers and Ecological Weed Management in Southeast Organic Cropping Systems: Weed Seedbanks and Weed Seed Predators by Aaron Freeman Fox A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy