Biological Control of Weeds in Corn and Soybean with Dwarf Brassica Smother Plants

Project Overview

Project Type: Research and Education
Funds awarded in 1992: $0.00
Projected End Date: 12/31/1995
Matching Non-Federal Funds: $36,000.00
ACE Funds: $67,000.00
Region: North Central
State: Minnesota
Project Coordinator:
Donald Wyse
University of Minnesota

Annual Reports


  • Agronomic: corn, soybeans


  • Crop Production: crop rotation, application rate management
  • Education and Training: demonstration, extension, on-farm/ranch research
  • Natural Resources/Environment: soil stabilization
  • Pest Management: biological control, field monitoring/scouting, weather monitoring


    In 1994 and 1995, field experiments were conducted in four geographical regions throughout Minnesota to evaluate the effectiveness of dwarf-Brassica smother plants for weed control in corn and soybeans. Additionally, the effects of dwarf-Brassica plants on crop growth and development and grain yields were examined under a variety of soil types and environments. In 1994, three seeding rates of dwarf-Brassica were evaluated. Two early season harvests were conducted for each crop at each site. Broadleaf and grassy weeds, dwarf-Brassica, and corn or soybeans were counted and harvested within specific, defined plot areas for each of the two early season harvests. In general, dwarf-Brassica plants were quite competitive with both corn and soybeans early in the crop growing season. Often, all three seeding rates of dwarf-Brassica resulted in smaller and/or fewer corn and soybean plants and sometimes delayed the crop's development. The visual differences were more apparent in corn than soybeans. Generally, the stunting effect only lasted until the middle of the growing season. The effectiveness of dwarf-Brassica for weed control was quite variable between sites in 1994. In some instances at least the highest seeding rate of dwarf-Brassica provided significant early season weed control.

    In 1994, late-season weed harvests were conducted near the end of the crop growing season at the three locations with the heaviest weed populations. Interestingly, dwarf-Brassica provided the best and most consistent weed control at the location with the greatest weed populations. In 1994 there were no apparent positive or negative effects of dwarf-Brassica on corn or soybean grain yields. However, the presence of weeds significantly decreased grain yields of corn and/or soybeans at three of the five locations. Therefore, it is possible that by providing weed control, the dwarf-Brassica may have had an indirect, but positive, effect on maximizing grain yields. It is important to note that growing conditions were optimal for corn and soybeans in Minnesota in 1994, and weed pressure was fairly light at four of the five experiment locations, which was due to past weed control practices and favorable growing conditions. The experiments conducted at four locations in 1995 were similar to the 1994 studies except that another dwarf-Brassica seeding rate was added that was twice the highest seeding rate used in 1994.

    Additionally, the 1995 experiments were conducted in fields with high weed populations to most accurately assess the ability of dwarf-Brassica to control weeds in corn and soybeans. In 1995, climate was the most important factor affecting the performance of dwarf-Brassica. The 1995 growing season was very different from 1994 and was characterized by a cool to normal spring followed by a hot dry early summer, based on 30-year averages. The dwarf-Brassica smother plant we have been developing is a cool season plant that typically will germinate well under the cool spring conditions often found in Minnesota, and then will near the end of its life cycle by mid-summer. The average temperatures in mid-June of 1995 were several degrees above normal, while precipitation was below normal. The hot, dry weather experienced in mid-June occurred during the beginning of the dwarf-Brassica reproductive growth phase which is when most plants are especially vulnerable to environmental stress. Because the growth and development of dwarf-Brassica was delayed or arrested during mid-June at most sites in 1995 it was not able to compete very well with weeds found at these locations.

    In 1995 the presence of weeds significantly decreased grain yields at all of the corn experiment locations and three out of four soybean locations. The dwarf-Brassica seeding rate generally had no effect on crop grain yields except at the south central Minnesota location where all but the lowest seeding rate of Brassica decreased corn grain yields. This site was the one location where dwarf-Brassica was the least affected by the high early season temperatures. Dwarf-Brassica was able to achieve maximum ground cover at this location and was fairly competitive with corn but did not suppress weed growth enough to eliminate yield reductions due to weeds. Based on the past two years of field research, climate had the greatest impact on the ability of dwarf-Brassica to compete with and control weeds. Additional research is needed to further determine the effectiveness of dwarf-Brassica for weed control in corn and soybean systems in Minnesota.

    Project objectives:

    1. Develop dwarf-Brassica smother plants for weed control in soybeans and corn through classical plant breeding.

    2. Evaluate the effectiveness of dwarf-Brassica smother plants for controlling weeds and reducing soil erosion.

    3. Identify the factors that could impede the adaptation of the dwarf-Brassica smother plant system by corn and soybean producers.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.