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

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

Summary

A comparison of organic, fresh-market, and processing tomato farms in Indiana suggested that, although some weed species are common to all three systems, yellow nutsedge, barnyardgrass, goosegrass, and Pennsylvania smartweed are particular problems for organic growers. Organic farms differ substantially from conventional farms in a number of characteristics including size, reliance on cover crops, and labor inputs. Conventional tomato production in Indiana is highly standardized with relatively little variation in practices among farms. In contrast, organic farmers in Indiana vary widely in their management practices. Conventional tomato farmers may be reluctant to transition to organic production until management practices become more standardized. Thus, there is considerable need for research on optimal weed management practices in organic agriculture.

Objectives/Performance Targets

1. 1) Increase interaction among farmers, extension personnel, and researchers by organizing an advisory board committed to facilitating research on organic vegetable crop production.
   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. We are preparing outreach materials based on our research and will submit these materials to the board before making the materials available to the public. We began the transition of 16 acres at Purdue University to organic. We will expand our current board and rely on their input to structure research and outreach activities during the transition and after certification. This will further increase and improve interaction among farmers, extension personnel and researchers.

Objective 2. A detailed questionnaire regarding weed management practices and farming systems was developed and disseminated during 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.

Our analyses clearly distinguished among processing and organic tomato management systems, even when herbicide use was not included as a variable. Organic farmers used cover crops more frequently, had more hours per acre of manual weeding, and used wider row spacing than processing farmers. Organic growers relied more heavily on plastic mulch than fresh or processing. Organic and fresh market fields were much smaller than processing fields (0.5 and 1.3 hectares vs. 28.1 hectares, respectively). Although processing and organic farms differed substantially in management practices, fresh market tomato farms had practices common to both organic and processing farms. Finally, management practices were very similar among processing farmers but varied widely among fresh market and organic farmers. For conventional farmers accustomed to relying on a set of highly standardized practices, transitioning to a system that lacks clearly defined and common management practices, particularly for weeds, may be difficult. Our study suggests the need for research on optimal weed management practices in organic tomato production.

Weed species richness and abundance were greater for organic tomatoes than for processing and fresh-market tomatoes. Although many weed species were common to all three management systems, some species were associated with specific farming practices and systems. Giant ragweed was associated with processing farms, but not with organic; this may reflect the rotation of agronomic crops (corn, soybean) on processing farms. Giant ragweed is the primary weed pest in corn and soybean in Indiana. Yellow nutsedge, barnyardgrass, goosegrass, and Pennsylvania smartweed were associated with the use of cover crops in organic systems. Thus, our research suggests that the three farm systems differ not only in management systems, but also in weed communities and weed abundance.

Soil cores were collected at the same time that fields were sampled for weed species in order to obtain estimates of species diversity in the soil seedbank. We are currently employing a seedling emergence technique to determine soil seed bank composition. Soil seedbank data will be used to further assess the cumulative effect of weed management techniques on weed species richness and abundance.

Objectives 3 and 4. We are in the process of developing and disseminating outreach materials. We anticipate the development of a website devoted to weed management in organic tomatoes during final year of the grant.

Impacts and Contributions/Outcomes

First, this project has led directly to increased collaboration among farmers, extension personnel, and researchers. We anticipate additional and increased levels of collaboration as we develop land for research on organic agriculture at Purdue University. Second, we have identified differences among management systems and weed communities in processing, fresh-market, and organic tomatoes. This information should help farmers evaluate issues involved in the transition from conventional to organic agriculture. Finally, we will work with our advisory board to disseminate the results of our research to conventional and organic growers.