Increasing biological control of brassica pests through overwintering

Increasing biological control of brassica pests through overwintering

Summary

Bryan O’Hara, a diversified organic farmer, has found that his pest problems in brassicas have been much reduced since he began overwintering some brassicas and allowing them to flower in the spring. We will test how widely this observation applies on two organic farms with overwintered brassicas and two organic farms without overwintered brassicas (but with other early flowering plants, such as overwintered carrots or parsley). On these four farms, we will collect the insects on the flowering plants in the spring to determine if parasitoids or predators of the insect pests of brassicas are more abundant on the farms with overwintered brassicas, and we will set out imported cabbageworms on potted plants in the spring and summer to see if the rate of parasitism differs.

Objectives/Performance Targets

• Summer 2006: Establish a colony of imported cabbageworms at the Connecticut Agricultural Experiment Station, and test the above protocol for parasitism tests to determine if this number of larvae and length of exposure will be sufficient to measure parasitism levels on organic farms.

  Fall 2006: Plan with the farmers the location of the overwintered brassicas and other flowering plants (such as parsley or parsnips) to be sampled the following spring. Collect information from farmers about when they plant and harvest their brassica crops, the methods used in overwintering brassicas, and the cost of materials for overwintering brassicas.

  Winter 2006-2007: Gear up imported cabbageworm colony so that it can produce 200 larvae per week in the spring of 2007.

  April – June 2007: Collect spring vacuum samples and conduct spring parasitism tests as described above. The spring parasitism tests require rearing out 1000 imported cabbageworm larvae (assuming the tests are conducted for 5 weeks) in order to determine rates of parasitism.

  August – September 2007: Conduct late summer – fall parasitism tests.

  June 2007 – December 2007: Sort vacuum samples, organize and enter data from the vacuum samples and parasitism tests.

  December 2007 – February 2008: Analyze data from all experiments, write up results for publication and presentation.

  March 2008: Outreach through grower meetings (conference of the Connecticut chapter of the Northeast Organic Farming Association ) and publication in Gleanings (CT NOFA newsletter) and on the CT Agricultural Experiment Station website.

  August 2008: Additional outreach through a workshop at the regional NOFA Summer conference.

Accomplishments/Milestones

As planned, we have established a colony of imported cabbageworms that we expect to carry through the winter to use in experiments this coming spring. We did one trial run of a parasitism test in the field (not at the farms under study – it was just to practice the procedures). And, we had a meeting with the four farmers who are cooperating to determine what crops they are overwintering and how much area they will overwinter of each crop.

Impacts and Contributions/Outcomes

The experiments for this project will be carried out this coming spring, so there are no outcomes from the research. Just before this project began (in March 2006), we held a twilight meeting at Tobacco Road Farm, in cooperation with Ruth Hazzard, who leads a SARE project on improving production of brassicas. Bryan demonstrated his methods for overwintering brassicas, and showed his overwintered crops, which were ready to harvest in March. This meeting was attended by about 30 farmers, and an article about this meeting was the featured article and front cover of Gleanings, the newsletter of the Connecticut Northeast Organic Farming Association, reaching over 600 CT NOFA members.

Collaborators: