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 organic farms had more weedy individuals and weed species than processing and fresh market farms. However, no single weed species dominated on the organic farms while giant foxtail was particularly abundant on the processing farms. This suggests that selective pressure favoring the dominance of a particular weed species may be lower in organic tomato production. Only eastern black nightshade was found in all three systems. Analyses are being conducted to determine how management factors affect the abundance and dominance of weed species in each management system.

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.
  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 will submit all outreach materials to the board before making the materials available to the public to insure the clarity and effectiveness of our outreach efforts.

Objective 2. A detailed questionnaire regarding weed management practices and farming systems was developed and disseminated during fall 2002 and early winter 2003 to a group of 25 production, fresh market and organic tomato growers in Indiana. Growers were recruited during extension meetings, conferences, and from recommendations from the advisory board.
The identity and relative abundance of weed species were determined by sampling fields in 2003. Species richness and abundance were greater for organic tomatoes than for processed and fresh market. Some weed species were common to all management systems. For example, Eastern black nightshade was found in all three systems. Redroot pigweed and giant foxtail were found in two of the three systems. Giant foxtail was particularly abundant in fields farmed for processing tomatoes. This suggests that giant foxtail may be particularly well-adapted to weed management practices used by processed tomato farmers. In contrast, while the organic fields contained more weed species, no single weed species dominated. This suggests that selective pressure favoring the dominance of a particular weed species may be lower in organic tomato production.
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 seedbank composition. Soil seedbank data will be used to further assess the cumulative effect of weed management techniques on weed species’ richness and abundance.
We are conducting multivariate analyses to characterize the relationships between farm management practices and weed communities and control. Questionnaires will be redistributed during winter 2003-04 and tomato fields will be sampled in 2004. We hope to recruit an additional five to seven organic farmers into the project in 2004

Objectives 3 and 4. We will develop and disseminate outreach materials in the third and final year of the project. We anticipate the development of a website devoted to organic production in tomatoes during that phase of the grant.

Impacts and Contributions/Outcomes

Although we are still in the initial stages of data collection, our project has had the following impacts. First, we now have a pool of farmers with a direct link to Purdue University. We believe this group of farmers will improve our ability to prioritize weed management issues. We also believe they will serve as a resource for future on-farm research endeavors. Second, we have presented our preliminary results at two weed science regional conferences.