Managing weed seed rain: A new paradigm for organic and low-input farmers

Managing weed seed rain: A new paradigm for organic and low-input farmers

Summary

Field experiments examined effects of management for zero seed rain and practices that maintain weed seed rain at or near the soil surface to encourage losses due to predation and germination. Not surprisingly the zero seed rain effect was dramatic. For example, spring sampling of the germinable seedbank showed redroot pigweed averaged 30,000 seeds per square meter (10 cm depth); in flail-mowed, tilled cover crop and no-till cover crop, with no treatment effects, but 1,000 germinable seeds in the zero seed rain control. Barnyardgrass response was consistent with our hypotheses regarding greater seed loss with no-tillage (860 seeds per square meter) compared to a tilled cover crop (2,800 seeds per square meter). However, these treatments had similar effects on the other dominant weed species including redroot pigweed, common lambsquarters, low cudweed and marsh yellowcress. It appears that, inexplicably, predation levels were very low in the fall/over-winter period of 2008-2009; for all species, spring seedbank density was similar in samples collected within and outside seed predator exclosures. After the dramatic exclosure effects documented in the 2007-2008 field season this was unexpected, but demonstrates the potentially large variability in predation effects. Management to enhance predation losses has consistently been equal to tillage-based treatments, but only in one of three years has it contributed to significant seed losses.

Objectives/Performance Targets

Through field days, meeting presentations, and published case studies, 150 New England vegetable and organic dairy farmers will learn about the Fall Weed Management Project; direct-mail and follow up telephone surveys will demonstrate that one third of this target audience implemented a new strategy focused on fall weed management, with 10% of the group adopting multiple tactics to preempt seed rain and maximize weed seed predation and mortality.
Evidence Performance Targets Have Been Reached
1. Attendance at on-farm site field days and grower meetings will reach an audience of over 300 mixed vegetable growers.
2. Surveys of growers in cooperation with the Maine Organic Farmers and Gardeners Association (MOFGA) and the Northeast Organic Farming Association (NOFA) will indicate the number of growers implementing strategies for weed seed rain management, and the source of their information.
3. Requests for information and on-farm visits will be used as an indicator that performance targets are being met.
4. Lastly, we will anonymously review MOFGA applications for organic certification (for growers who agree to participate in the survey) from a one- to three-year period prior to implementation of our project, and applications submitted in the fall and winter of 2008, recording the proportion of applicants implementing weed seed rain management practices.

Accomplishments/Milestones

1. Ten grower participants are selected based on individual meetings with 15 or more candidate growers.
2. On-farm tactics are selected by growers and researchers for implementation in the fall of two consecutive field seasons; tactics are implemented and maintained by project team.
3. Field days and talks at winter meetings present tactics to target audience.
4. Experiences are summarized in case studies to be published jointly by UM Cooperative Extension and the Maine Organic Farmers and Gardeners Association.
5. Surveys are conducted to document outcome. ?

To prepare case studies of growers with a range of weed seedbank management philosophies we resampled two farms that were originally sampled as part of a 2001 NESARE project, the Peacemeal Farm in Dixmont, Maine, and the New Leaf Farm in Durham, Maine. This is an exciting opportunity to resample fields and examine changes in the weed community and relative abundance of problem species over eight years of management. We also sampled the Beech Grove Farm of Eric and Anne Nordell who are well known for their intensive rotation and cover cropping strategies, and a weed management philosophy that focuses on the seedbank.

Weed communities were comprised of an average 8 to 10 species on each farm. The three most abundant species at the Peacemeal Farm, redroot pigweed, common lambsquarters and hairy galinsoga, are a widespread problem among northeastern vegetable growers. At the New Leaf Farm, smooth crabgrass was the top-ranked species, primarily because of a large infestation in a field where pigs had been pastured. The number two- and three-ranked species, low cudweed and corn spurry, while a problem in salad mix, are not particularly troublesome in most other vegetable crops. At the Beech Grove Farm, typically pernicious summer annual weeds were rare and not among the top ranked species which included marsh yellowcress, mouseear chickweed and Virginia strawberry. Mean seedbank density at the Beech Grove Farm was 550 germinable seeds per square meter (10 cm depth); this compares to 5,000 and 12,500 germinable seeds per square meter at the New Leaf and Peacemeal Farms, respectively. The focus on managing the weed seedbank at Beech Grove is clearly reflected in this small dataset which represents the low, medium and high seedbank conditions that are found on diversified organic vegetable farms.

To complete the replicated field trials, we established a final field study at the University of Maine’s Witter Farm in the fall of 2009. We considered the site ideal for the Seed Rain Project as the wet field season of 2009 resulted in an abundant and uniform stand of large crabgrass in a soybean field at this site. We included four treatments as in previous years: standard fall tillage with cover crop (tilled/cover crop), No-seed rain, No-till planting with cover crop (no-till/cover crop) and Flail mow with no tillage and no cover crop (flail/no-till/no cover crop). We also included a moldboard plow treatment, based on questions from growers who have considered deep plowing to bury seed rain of relatively non-persistent species, including many annual grass species. To measure seed rain we implemented a new sampling methodology using vacuum cleaners to collect surface seed from a known area. These samples are presently being sub-sampled, sieved and sorted by hand to identify weed seeds.

Impacts and Contributions/Outcomes

There has been an increasing interest in the topic of weed seedbank management at local and regional grower meetings. The new datasets from Managing Weed Seed Rain were featured at three invited presentations during the 2009 calendar year, and a symposium at the Northeast regional weed science meeting in early 2010:

• Managing Weed Seed Rain. Northeast Weed Science Society Annual Meeting, Symposium on Weed Seedbanks (5 January 2010).

• Managing Weeds with Crop Rotation. New England Vegetable and Berry Conference, Manchester, NH (16 December 2009).

• Gallandt, E.R. (2009). Managing weed seed rain to enhance physical weed control efforts. 8th European Weed Research Society Workshop on Physical and Cultural Weed Control, Zaragoza, Spain (9 March 2009).

• Seed Rain Project — Weed Master. Maine Agricultural Trades Show, Augusta, ME (13 January 2009; 75 attending).

The on-farm seedbank sampling has been of great interest to growers, used as a handout by Eric and Anne Nordell during their recent presentations (seed attachment), and posted to the University of Maine Weed Ecology Group Blog (gallandt.wordpress.com).

• Handout used at grower meetings.
• Sampling fall weed biomass and seed production; Sept. 23, 2009
• Soil sampling the Nordell’s home garden plots
• Crabgrass-infested organic soybeans and weed-free plots for 2009-2010 field experiment
• Vacuuming to sample fall weed seed rain, UMaine Witter Farm, Sept 23, 2009

Collaborators: