Southeast Exotic Pest Plant Council

EVALUATION OF CLOPYRALID, FLUROXYPYR, METSULFURON METHYL, AND TRICLOPYR FOR SCOTCHBROOM CONTROL. M.P. Blair; Department of Agronomy, University of Kentucky, Lexington, KY and S.M. Zedaker; Department of Forestry, Virginia Tech, Blacksburg, VA. (


Scotchbroom (Cytisus scoparius L.) is a perennial woody shrub that is present in 25 of the 50 United States. This federally listed invasive species is native to Europe and was introduced in California in the late 1800's as an ornamental plant and soil stabilizer. The continued ornamental use of this leguminous plant has contributed to its spread across the continental United States and Hawaii. Scotchbroom can establish itself on a variety of sites, including dry upland sites. Scotchbroom readily establishes in open environments during early succession. Individual plants may produce up to 60 seed pods by the second year of growth with each pod containing 5-8 seeds. This fecundity and rapid growth rate have contributed to failures in Douglas-fir plantations in the Pacific Northwest. Dense stands of scotchbroom may also interfere with right-of-way access and maintenance. This troublesome species is beginning to invade the Piedmont and Coastal Plain physiographic regions of the southeastern United States.

A study was initiated in August, 2003 to evaluate chemical control options for scotchbroom. Seven chemical treatments and one untreated control treatment were evaluated in a completely randomized design study with four replications in the Coastal Plain region of Virginia. Plots were installed along a forest road and were 25' X 15'. Treatments included Garlon 4 (triclopyr ester) at 0.5, 0.75, and 1 lb a.i. per acre, Escort (metsulfuron methyl), at 2.4 oz a.i. per acre, Escort plus Garlon 4 at 1.2 oz a.i. and 0.5 lb a.i. per acre, respectively, Garlon 3A (triclopyr amine) plus Vista (fluroxypyr) at 1 lb a.i. and 0.5 lb a.i. per acre, respectively, and Transline (clopyralid) plus Vista at 0.5 lb a.i. and 0.5 lb a.i. per acre. All treatments included a nonionic surfactant at 0.25% v/v and were applied as a roadside foliar spray using a CO2 powered sprayer equipped with BoombusterTM tips mounted on an ATV. Application volume was 20 GPA.

Data were collected at pre-application, 7 weeks after treatment (WAT), and 40 WAT. Green scotchbroom and brown (dead) scotchbroom horizontal line intercept counts were made at one foot intervals. This data was then transformed into percent cover by plot and analyzed using analysis of covariance (preapplication data as the covariate) in SAS®. Least squared treatment means were compared using Tukey-Kramer HSD at p = 0.05.

All treatments reduced percent cover of live scotchbroom to less than 10% 7 WAT and maintained this reduction in cover 40 WAT. Garlon 4 alone reduced scotchbroom cover to less than 5% 7 WAT and maintained a reduction the following growing season regardless of rate used. Escort provided a reduction in cover to 9% 7 WAT and further decreased cover to 0% 40 WAT. The Escort / Garlon 4 tank mix increased cover between 7 and 40 WAT, yet still had satisfactory control. The Transline / Vista tank mix was the only treatment to reduce percent cover to 0% at 7 WAT and maintain the 0% cover level the following growing season.

Growth regulator herbicides (Garlon, Vista, and Transline) are effective control options for scotchbroom. This is consistent with past studies. Escort, a sulfonylurea herbicide in the ALS inhibitor class of herbicides, is an effective control option. Imazapyr, an imidazolinone herbicide also belonging to the ALS family, has been shown to be ineffective in controlling scotchbroom. This comparison shows that two compounds with the same mode of action but different chemical structures may have different control results. Further rate titrations of the growth regulator herbicides should be examined for cost efficacy, control options, and crop sensitivity (i.e. southern yellow pine). Additional studies are needed to determine if retreatment can eradicate scotchbroom in southern yellow pine plantations.

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