Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2018
Publication Date: 4/4/2018
Citation: Teasdale, J.R., Mirsky, S.B., Cavigelli, M.A. 2018. Meteorological and management factors influencing weed abundance during 18 years of organic crop rotations. Weed Science. 1:8. https://doi.org/10.1017/wsc.2018.15.
Interpretive Summary: Weed management represents one of the largest challenges for organic grain farmers because weeds, which can reduce crop yields substantially, can be difficult to control without herbicides. An analysis of 18 years of weed cover data in three organic crop rotations at the long-term Farming Systems Project in Beltsville, Maryland, showed that the interaction between weeds, corn and soybean production were complex. Delaying crop planting date and increasing the number of crops other than corn and soybean in the rotation decreased weed abundance but had little effect on crop yields. Using a rotary hoe to control weeds reduced weed abundance but also damaged crops. Precipitation during late vegetative and early reproductive crop growth stages improved crop production, which was the most important factor impacting weed cover. Results show that practices that favor corn and soybean competitiveness seem to provide the most effective weed management in organic grain production systems. These results will be of interest to organic farmers, crop consultants, government agencies such as USDA-AMS, other scientists, and policy makers.
Technical Abstract: Organic crop production is often limited by the inability to control weeds. An 18-year dataset of weed cover in organic crop rotations at the long-term Farming Systems Project at Beltsville, Maryland, provided the opportunity to identify meteorological and management factors influencing weed abundance. A path analysis using structural equation models was employed to distinguish between the direct effect of factors on weed abundance compared to the indirect effect by way of effects on crop performance. Corn and soybean grain yield served as a surrogate for overall crop competitiveness, and was found to be the most important factor influencing weed cover. Precipitation during late vegetative and early reproduction crop growth had a strong positive effect on crop yield, and thereby a negative indirect effect on weed cover, but this effect was offset by a positive direct effect on weed cover. Delayed crop planting date and crop rotational diversification to include crops other than the summer row crops, corn and soybean, both had a moderate negative effect on weed abundance, while having minimal effect on crop performance. Rotary hoeing also had a direct negative effect on weed abundance, but a corresponding negative effect on crops resulted in an offsetting positive indirect effect on weeds. Results demonstrate the complex interactions that define the relative abundance of weeds faced by organic growers each season, but, generally, practices that enhance crop competitiveness should provide the most effective basis for successful weed management.