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At the Joint Base Lewis-McChord military installation near Tacoma, Wash., efforts to thwart a flowery intruder are benefiting significantly from U.S. Department of Agriculture (USDA) backup. Agricultural Research Service (ARS) entomologists helped resource managers at the base evaluate different strategies for controlling flourishing thickets of Scotch broom (Cytisus scoparius), a native European perennial that can grow more than six feet tall. ARS is USDA's chief intramural scientific research agency.
To date, the plant has been controlled at Fort Lewis with some success by using controlled burns, mowing, or by releasing a biological control agent, the Scotch broom seed weevil. The mowing and burning control strategies had been applied to many Fort Lewis sites for at least 20 years. Previous research suggested that burning did not disrupt the native prairie plants, but sometimes Scotch broom that was mowed came back even more vigorously, an outcome that could result in an endless loop of ineffective eradication efforts.
ARS research leader Ray Carruthers and ARS entomologist Angelica Reddy evaluated options for controlling the vegetation with different combinations of weevil seed predation, mowing, and burning. Both scientists work at the ARS Exotic and Invasive Weeds Research Unit in Albany, Calif.
The team assessed the effectiveness of different measures by surveying pods and plants for two seasons to measure seed production, seed predation by the weevils, weevil numbers in pods, and seed bank densities. They found that combining weevil predation with either burning or mowing reduced the number of pods per plant, healthy and mature seeds per plant, and seed bank densities significantly more than just using weevils alone.
As a result of their findings, the researchers believe using 3-year rotation fires with seed predation could improve long-term efforts to control Scotch broom at Fort Lewis.
Results from this study were published in 2012 in Invasive Plant Science and Management, and the paper received an award from the Weed Science Society of America in 2013 for the "Outstanding Paper in Invasive Plant Science and Management."
Read more about this work in the October 2013 issue of Agricultural Research magazine.