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UNH scientists join effort to identify most common weeds

March 07. 2018 12:04AM
UNH graduate student Sarah Levy and Dr. Sidney Bosworth with the University of Vermont Cooperative Extension examine an unusual lambsquarters plant in the UNH Macfarlane Research Greenhouses. (Courtesy of UNH)

DURHAM — Scientists from Maine, New Hampshire, and Vermont have completed the first comprehensive assessment of weeds found on organic vegetable farms in Northern New England.

“The purpose of this project was to establish a baseline assessment of the weed problems facing organic vegetable growers in the Northern New England region as a basis for detecting and predicting the evolutionary emergence of new, problematic weeds,” said New Hampshire Agricultural Experiment Station researcher Dr. Tom Davis, professor of genetics at the University of New Hampshire.

“Even weeds that are currently rare or non-existent in certain areas of our region may become more prevalent in the future due to changes in our environment, and those should be of concern to any farmer, whether they are organic or not,” said experiment station researcher Dr. Richard Smith, associate professor of natural resources and the environment at UNH.

According to a UNH news release, Maine, New Hampshire, and Vermont encompass a large degree of climate and soil variation across a relatively small area, making it ideal for studying climate and other environmental change impacts on agricultural weed communities.

Scientists sampled weed seedbanks and measured soil physical and chemical characteristics on 77 organic farms across the region. They found temperature-related variables such as latitude, longitude, and mean maximum and minimum temperature were the strongest and most consistent correlates with weed seedbank composition, the news release states.

Researchers discovered that at least some weed species in the region are much more genetically diverse than had been previously recognized.

Scientists identified 113 weed species in soil seedbank samples collected across the 77 farms. The most abundant weed species, in terms of total number of seedlings that emerged from the seedbank samples, were from highest to lowest: slender rush, hairy galinsoga, common purslane, Veronica spp., common lambsquarters, redroot pigweed, large crabgrass, and low cudweed.

Together these accounted for nearly 73 percent of the seedlings.

No species were present in all 77 sites; however, nine species occurred in at least 65 percent of the sites. These nine species were:

• Common lambsquarters (observed in 95 percent of the farms),

• Large crabgrass (82 percent);

• Redroot pigweed (78 percent);

• Hairy galinsoga (70 percent);

• Slender rush (68 percent);

• Common chickweed (68 percent);

• Veronica spp. (68 percent);

• Yellow woodsorrel (66 percent);

• Broadleaf plantain (65 percent).

According to the USDA’s most recent Certified Organic Survey released in 2017, the total value of sales of organic vegetables in Maine, New Hampshire, and Vermont is $23.2 million.

“Weeds continue to be one of the most difficult management challenges that organic farmers face. Our research has not only provided a much clearer picture of the weed species present in our region, it has also provided farmers with a ‘heads up’ in terms of which particular weeds they can expect to see more (and also less) of in the near future. Such information is useful to both farmers and researchers who are trying to develop new and more effective management strategies for dealing with weeds,” Smith said.

“Ultimately, weed control practices influence the quality, price, and availability of locally grown produce. Thus, efforts to monitor and perhaps forestall the emergence of new weed species serve the interests of consumers seeking affordable, high-quality, locally grown produce,” Davis said.

In addition to Davis and Smith, collaborators on this project include Dr. Eric Gallandt, professor of weed ecology at the University of Maine; Dr. Sidney Bosworth, University of Vermont Cooperative Extension professor of crop science; Dr. Ann Hazelrigg, University of Vermont Cooperative Extension assistant professor of plant pathology; Nick Warren, graduate student and manager of the UNH agroecology laboratory; Sarah Levy, UNH graduate student in genetics; and Sonja Birthisel and Bryan Brown, graduate students in ecology and environmental sciences at the University of Maine.

This research was funded by the Northern New England Collaborative Research Funding Program, a partnership of the Maine Agricultural and Forest Experiment Station, New Hampshire Agricultural Experiment Station, and the Vermont Agricultural Experiment Station.

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