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    Saturday, April 01, 2023

    Knowledge is power when it comes to horseweed

    Master Gardener Dr. Judith Allik holds a bunch of horseweed with seeds in a Pawcatuck parking lot in September 2022. Photo by Jan Tormay
    Master Gardener Dr. Judith Allik shows horseweed coming up through a crack in a Pawcatuck parking lot in September 2022. She predicts there will be much more of this invasive weed everywhere this year. Horseweed will grow wherever there are bare patches in lawns, as well as in asphalt cracks, sidewalk crevices, in parks and on streets, she said. Photo by Jan Tormay
    This photo of a young horseweed plant was taken by Dr. Jatinder Aulakh, an associate weed scientist at the Connecticut Agriculture Experiment Station in Windsor.
    Horseweed in its beginning rosette stage. This invasive plant often grows seven feet tall, but can grow as high 10 feet. Photo by Dr. Vipan Kumar, Cornell University
    Small, young Palmer amaranth weeds in cornfield. Photo by Dr. Jatinder Aulakh, CAES Windsor Connecticut
    The invasive Palmer amaranth weed in reproductive stage. Photo by Dr. Jatinder Aulakh, CAES Windsor Connecticut

    After Dr. Judith Allik moved from Voluntown to Stonington’s Pawcatuck Village last spring, she noticed horseweed everywhere - bare patches on lawns, in asphalt cracks and sidewalk crevices, in parks and on streets. Since she had never seen the weed before, the retired Voluntown school psychologist began doing research.

    She later spotted it all over downtown Cambridge, Massachusetts, when she visited her sister-in-law.

    “The best way to get rid of it is to pull it,” said Allik, a graduate of University of Connecticut’s Master Gardener Program. She pulled at least 3,000 of these “feathery” plants from bare spots in her new home’s backyard last year and hopes she will not have to do it again this spring.

    She said horseweed is not a new weed. “What’s new is a lot of the farmers are going to no-till farming,” because plant roots hold down the soil and prevent soil erosion.

    “The farmers that are doing that are having a much, much more difficult time with horseweed than the farmers that are plowing, because when they plow, the dirt goes over the existing seeds and they don’t germinate.”

    Horseweed, also known as horsetail, marestail and Canada fleabane, is an annual weed native to North America, which can “follow a winter or summer annual life cycle. After emergence in the fall, horseweed forms a basal rosette for winter survival. In a winter annual life cycle, the rosette bolts in the spring, growing to a height of 1.5 to 6 feet,” according to extension.purdue.edu/extmedia/gwc/gwc-9-w.pdf.

    “Horseweed leaves are alternate, linear, and simple with entirely or slightly toothed margins. ... Leaves get progressively smaller in size toward the top of the plant.”

    At six feet, horseweed can produce over 230,000 seeds in early spring or in the fall and be carried by the wind to other places, said Dr. Jatinder Aulakh, associate weed scientist at the Connecticut Agriculture Experiment Station in Windsor in an email.

    “It has already established itself as a problematic weed in Connecticut agronomic, ornamental, and horticultural crops.”

    Aulakh stated that horseweed contains specialized chemicals that “can inhibit germination and growth of several other plant species.”

    He said Christmas-tree farm owners have been managing this invasive plant with herbicides.

    Possible solutions

    Even though horseweed has developed resistance to many different herbicides, Aulakh said it is easy to control with the right kind of herbicide depending upon the site it is growing in.

    Allik predicts horseweed will become more of a problem with every passing year. She urges people to pull the weed out as soon as they see it in the spring.

    “They pull up very easily when they’re young and they don’t regrow,” she added.

    Allik said if you’re a faithful mower and mow every week, only the tops of the weed are being cut off and the roots and tentacles keep growing – at which point it is very difficult to pull the weed.

    “If you’re a 250-pound guy, maybe,” she said, but if it breaks off, it will still come back.

    Ways to rid properties of horseweed without using chemicals include “repeated mowing, planting cover crops, and tillage in field crops,” as well as hand-pulling, Aulakh said.

    He agreed with Allik that if horseweed is mowed over, it will come back with a vengeance. Mowing or uprooting depends on the scale of infestation, he added.

    “You may hand pull if there are a few plants here and there, but how about thousands of plants in a lawn or playground, etc.?”

    “If it is a dense infestation and on a scale not suitable for hand pulling, and people do not want to control it chemically, then mowing may be the only option.”

    Aulakh said organic farmers could also plant a cover crop, such as cereal rye, crimson clover or their own mix, in August or September to suppress or reduce its densities in the coming spring/summer.

    Now that she has developed an eye for horseweed, Allik said laughing, “I can spot them easily.”

    Beware of the Palmer amaranth weed

    Another weed to watch out for is Palmer amaranth, which “looks like redroot pigweed and water hemp,” said Dr. Jatinder Aulakh, associate weed scientist at the Connecticut Agriculture Experiment Station in Windsor, in an email.

    The weed averages 6 to 7 feet in height, but can reach 10 feet.

    Aulakh first discovered the weed in pumpkin fields in East Windsor in the summer of 2019. Prior to this time, it was commonly found in the South, he wrote on the CAES website.

    “There is zero tolerance for this plant. Therefore one should do everything, depending upon scale of infestation, such as physical suppression with cover crops, crop rotation, use of pre- and post-emergence herbicides, hand pulling the escaped plants before they set seeds.”

    This highly invasive summer annual plant in the pigweed (Amaranthaceae) family “is an extremely problematic weed in several crops which include: cotton, corn, soybean, cucurbits, and several vegetable crops,” he stated. “What is most concerning about this pigweed is its ability to rapidly evolve resistance to herbicides.”

    Since a single female plant can produce more than 600,000 seeds, “Preventing the pioneer Palmer amaranth plants from producing seed is the first line of defense and also the most effective strategy to prevent its establishment into new areas,” Aulakh stated.

    If a single Palmer amaranth plant is allowed produce seed, he said, “it may result in serious management issues in the following years and may also result in increased herbicide costs as well as significant losses in crop yield.”

    Jan Tormay, a longtime resident of Norwich, now lives in Westerly.

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