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ARS Home » Pacific West Area » Wapato, Washington » Temperate Tree Fruit and Vegetable Research » Research » Publications at this Location » Publication #369841

Research Project: New Technologies and Strategies to Manage the Changing Pest Complex on Temperate Fruit Trees

Location: Temperate Tree Fruit and Vegetable Research

Title: Better together? Combining cover crop mulches, organic herbicides, and weed seed biological control in reduced-tillage crop systems

item LEWIS, DANIELLA - Clemson University
item CUTULLE, MATTHEW - Clemson University
item Schmidt, Rebecca
item BLUBAUGH, CARMEN - Clemson University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2020
Publication Date: 10/5/2020
Citation: Lewis, D., Cutulle, M., Schmidt-Jeffris, R.A., Blubaugh, C. 2020. Better together? Combining cover crop mulches, organic herbicides, and weed seed biological control in reduced-tillage crop systems. Environmental Entomology. 49(6):1327-1334.

Interpretive Summary: Organic growers rely on tillage and other labor-intensive methods for weed management. These methods can be expensive and cause soil erosion. Using cover crops for weed control helps reduce soil erosion compared to other methods, but when the cover crop is terminated to allow for crop growth, weeds can again become an issue late in the season. Recently registered organic herbicides may help organic growers improve their weed control programs. However, these herbicides are based on strong acids and may harm natural enemies that consume pest insects or weed seeds. Researchers at the USDA-ARS in Wapato, in collaboration with Clemson University, tested cereal rye and crimson clover mulched cover crops in combination with the organic herbicides capric/caprylic acid and corn gluten meal. The combination of crimson clover and capric/caprylic acid was the most effective at controlling weeds. This treatment also increased yields of a tomato crop and reduced the incidence of a tomato disease. The organic herbicides did not reduce natural enemy activity and the presence of a cover crop increased weed seed consumption. This work will allow growers to better optimize their weed management programs by integrating chemicals with cover crops.

Technical Abstract: Organic growers rely heavily on labor-intensive mechanical tactics for weed management. The use of cover crop residues as a weed-suppressive mulch has allowed growers to reduce tillage,although weed pressure late in the season can be problematic as residues decompose. Recently developed organic herbicides may mitigate this problem by extending weed suppression in cover crop mulch systems, but may adversely affect beneficial insects that consume weed seeds and crop pests. We compare three killed cover crop mulch treatments (cereal rye, crimson clover, and fallow) and three organic herbicide treatments (capric/caprylic acid, corn gluten meal, herbicide free) in a two-year experiment to examine potential synergy between cultural, chemical, and biological tools for weed management. We also examined potential non-target effects of organic herbicides on beneficial insects and weed seed biocontrol. In both years, capric/caprylic acid herbicides reduced weed cover relative to both fallow and corn gluten meal treatments by approximately 16%. In the second year of our study, a combination of a strong establishment of crimson clover cover crop with organic herbicide had the greatest weed suppressive effects relative to a fallow control. In a second study, we found that cover crop/herbicide combination treatment increased tomato yields to 13-fold relative to a fallow control and reduced soil-borne pathogen incidence by 50%. The cover crop/herbicide treatment had the added benefit of increasing weed seed predation by 46% relative to manual weed control treatments. In both studies, the organic herbicides led to no obvious reductions in beneficial insect activity nor weed seed biocontrol. Organic herbicides may be a viable supplemental weed management tool with limited non-target effects in reduced-tillage systems. Streamlining cultural, chemical, and biological weed management tools is a perpetual challenge for farmers. However, our results suggest that their combined use may enhance weed control while reducing the need for tillage and its adverse environmental impacts.