Weed Community Shifts and Management Options in the Conversion to Organic Production Systems

2005 Annual Report for LNC02-220

Project Type: Research and Education
Funds awarded in 2002: $93,375.00
Projected End Date: 12/31/2006
Region: North Central
State: Indiana
Project Coordinator:
Kevin Gibson
Purdue University

Weed Community Shifts and Management Options in the Conversion to Organic Production Systems

Summary

Weed species respond to the cumulative effect of multiple practices employed within weed management systems. However, this response is rarely studied at the system level and the relationships among weed communities and management systems in crops are not well understood. We used a questionnaire, on-farm sampling, and multivariate analyses to identify five weed management systems used to produce tomatoes in Indiana: two conventional processing systems, an organic fresh market system, and two fresh market systems used by organic and conventional growers. The five systems differed primarily in the use of irrigation, cover crops, and in the extent to which hand weeding was used to control weeds. The number of hours spent hand-weeding was much greater in the organic system than in the other systems. Giant foxtail, common lambsquarters, prickly sida, and carpetweed were common in all systems. Eastern black nightshade was common in the processing and mixed fresh market systems but largely absent from the organic system. Barnyardgrass and goosegrass were common in the organic fresh market system but not in the other systems. Canonical correspondence analysis identified distinct associations between specific species and the management systems. Common purslane was strongly associated with the rain-fed, mixed fresh market system and barnyardgrass, goosegrass, yellow nutsedge, and green foxtail were associated with the irrigated, organic fresh market system. Weed densities in the organic system were not greater than in the other systems. However, large weed populations were present in all systems after control measures were completed for the season. Weed populations persist or increase when a set of species-specific environmental conditions are met. This research suggests that new approaches are needed in all five systems to reduce within-season weed survival and seed production in order to lessen the need for intensive weed management efforts in subsequent years.

Objectives/Performance Targets

1) Increase interaction among farmers, extension personnel and researchers by organizing an advisory board committed to facilitating research on organic vegetable crop production and by conducting on-farm research.

2) Quantify the effect of conventional, transitional and organic farm management systems on weed species composition and abundance.

3) Provide information on the potential advantages and limitations of weed management in organic systems to farmers and extension personnel.

4) Stimulate on-farm research on weed management systems in organic crop systems.

Accomplishments/Milestones

Objective 1. An advisory board was formed to facilitate on-farm data collection, to help assess the relative advantages and limitations of different vegetable systems, and to identify continuing and emerging problems in weed management. The board assisted in the development of a questionnaire and in identifying farmers who might participate in this project. A detailed questionnaire regarding weed management practices and farming systems was developed and disseminated 2003 and 2004 to a group of twenty-five production, fresh market, and organic tomato growers in Indiana. Growers were recruited during extension meetings, during conferences, and based on recommendations from the advisory board. We used on-farm sampling during 2003 and 2004 to determine the identity and relative abundance of weed species on fields managed by farmers who completed our questionnaire. We used multivariate statistical analyses to 1) classify tomato farms into weed management systems based on the questionnaires and 2) identify relationships between weed communities and management systems.

Objective 2. We used a questionnaire, on-farm sampling, and multivariate analyses to identify five weed management systems used to produce tomatoes in Indiana: two conventional processing systems, an organic fresh market system, and two fresh market systems used by organic and conventional growers. The five systems differed primarily in the use of irrigation, cover crops, and in the extent to which hand weeding was used to control weeds. The number of hours spent hand-weeding was much greater in the organic system than in the other systems. Giant foxtail, common lambsquarters, prickly sida, and carpetweed were common in all systems. Eastern black nightshade was common in the processing and mixed fresh market systems but largely absent from the organic system. Barnyardgrass and goosegrass were common in the organic fresh market system but not in the other systems. Canonical correspondence analysis identified distinct associations between specific species and the management systems. Common purslane was strongly associated with the rain-fed, mixed fresh market system and barnyardgrass, goosegrass, yellow nutsedge, and green foxtail were associated with the irrigated, organic fresh market system. Weed densities in the organic system were not greater than in the other systems. However, large weed populations were present in all systems after control measures were completed for the season. Weed populations persist or increase when a set of species-specific environmental conditions are met. This research suggests that new approaches are needed in all five systems to reduce within-season weed survival and seed production in order to lessen the need for intensive weed management efforts in subsequent years.

Objective 3. Three papers have been submitted to peer-reviewed journals. Two have been accepted for publication by Weed Science. We have also published an article entitled “Weed management systems in organic vegetable production” in The New Ag Network (NAN), a website that provides seasonal advice to growers interested in organic agriculture. We also have presented the results of this study at several weed science conferences.

Objective 4. This project involved 25 growers and required substantial interaction with the growers to collect information for the questionnaires and to sample fields for weeds. We anticipate that the long-term impact of this project will be increased use of on-farm research to study system properties in organic and conventional crops.

Impacts and Contributions/Outcomes

This project has advanced our understanding of weed management systems and weed communities in conventional and organic tomato production. Purdue University is in the process of transitioning 16 acres to organic. Our research and input from conventional and organic growers suggests that we should focus on economically viable practices to reduce late-season weed populations and decrease weed seedbanks in order to reduce weed emergence and lessen the need for within-season control, particularly handweeding. We will initiate research on this topic in 2006, focusing specifically on the use of cover crops and intercropping to manage late-season weeds in vegetable crops.