Timothy W. Miller

Effects of Herbicide, Tillage, and Grass Seeding on Wild Chervil (Anthriscus sylvestris)

Abstract Wild chervil is an invasive biennial or short-lived perennial weed introduced into North America that negatively impacts forage production and degrades habitat for native plant species. A 2-yr study using prebloom mowing followed by combinations of herbicide, tillage, and grass seeding was conducted in the Pacific Northwest to identify an effective integrated weed management strategy for this species. By 2 mo after herbicide treatment (MAHT), wild chervil control with glyphosate + ammonium sulfate (AMS) and clopyralid was 83 and 73%, respectively. Tillage with or without herbicide pretreatment resulted in 92 to 98% wild chervil control at 2 MAHT, whereas herbicide without tillage gave only 45% control across all treatments. Tillage with or without subsequent grass seeding reduced wild chervil density four-fold compared to herbicide alone at 9 MAHT. Herbicide + tillage + grass seeding resulted in similar wild chervil cover (1 to 5% cover) as herbicide + tillage (1 to 6% cover) without subsequent grass seeding. Wild chervil biomass at 1 yr after herbicide treatment (YAHT) was reduced to 487 kg ha−1 (439 lb ac−1) with herbicide + tillage compared to 4,256 kg ha−1 for herbicide treatment alone. Herbicide + tillage + grass seeding increased grass dry weight at 1 YAHT from 201 kg ha−1 for herbicide + tillage to 1,575 kg ha−1, compared to 351 kg ha−1 in herbicide-only plots. Nomenclature: Clopyralid; dicamba; glyphosate; triclopyr; 2,4-D; wild chervil; Anthriscus sylvestris (L.) Hoffmann. Interpretive Summary: Wild chervil is an introduced biennial or short-lived perennial species found in the northeastern and midwestern states and adjacent Canada, as well as in middle Atlantic states and the Pacific Northwest. Control of this invasive plant is desirable, given its ability to reduce forage yield and quality, and to degrade native habitat. Mowing wild chervil prior to treatment with herbicides moderately increases control, but the impact of tillage on wild chervil control previously has not been examined. Because chemical or mechanical control of weeds in pastures and natural areas often results with injury to or elimination of nontarget plant species, revegetation of the site using well-adapted or native species generally must follow weed-control efforts. With these facts in mind, an integrated weed management strategy for wild chervil was developed that utilized prebloom mowing, herbicide application, and tillage, followed by seeding of well-adapted perennial grass species. An experiment was designed to test the effectiveness of this strategy, and two trials were conducted in the state of Washington from 2003 to 2005. Tillage as used here provided 92 to 98% control of wild chervil at 2 mo after treatment, with or without a pretillage herbicide application. At 1 yr after treatment, wild chervil biomass was reduced nine-fold if plots were tilled after herbicide application, but seeding grass into tilled plots was necessary to increase grass biomass. In areas where tillage such as used here is not possible, glyphosate application should provide satisfactory control of wild chervil. Because wild chervil seed does not persist long in the field (often surviving only one winter), lasting control of this invasive weed species likely will result from a consistently-applied integrated control strategy such as presented here.

Integrated Strategies for Management of Perennial Weeds

Multiple weed control strategies employed in combination can often aid the successful management of perennial weed species. This review article provides examples of integrated control programs that could aid in the management of several invasive perennial weed species that are problematic in the Pacific Northwest and elsewhere in North America. The development of an integrated management control program for wild chervil, a relatively recent invader to the Pacific Northwest of the United States and adjacent Canada, provides an example for this process. Through use of mechanical (mowing and tillage), cultural (establishment of competitive vegetation), and chemical (specific herbicides) strategies, control of this short-lived perennial species was greatly improved as compared to foliar herbicide applications alone. Such integrated strategies have been shown to enhance control of many perennial weed species, while potentially reducing the amount of herbicide applied, lessening the possibility of injury to adjacent desirable vegetation and increasing the stability of the ecological community at the site. Nomenclature: Aminocyclopyrachlor; aminopyralid; clopyralid; dicamba; fluazifop; fluroxypyr; glyphosate; imazapic; imazapyr; imazethapyr; mecoprop; picloram; triclopyr; 2,4-D; wild chervil, Anthriscus sylvestris (L.) Hoffmann.

Meadow Knapweed (Centaurea debeauxii) Response to Herbicides and Mechanical Control

Abstract Meadow knapweed is a fertile European hybrid between black and brown knapweed that has expanded its North American distribution to 27 of the United States and four provinces in Canada. Two experiments were conducted on meadow knapweed in northwestern Washington to determine (1) whether meadow knapweed is similarly sensitive to several herbicides commonly used to control related knapweeds, (2) if herbicide application timing plays a role in control of meadow knapweed, and (3) whether mowing before, after, or instead of herbicide treatment can aid in meadow knapweed control. In the first experiment, herbicides were applied to meadow knapweed at rosette or bolting stages of growth, and again with the same herbicides in the autumn. In the summer following treatment, clopyralid alone or with 2,4-D, dicamba + 2,4-D, and triclopyr ester + 2,4-D ester provided 81 to 100% meadow knapweed control; the only other treatment providing similar control was glyphosate + ammonium sulfate applied at bolting and in autumn in the 2004 to 2005 trial. In the second experiment, combinations of mowing and dicamba + 2,4-D were applied at rosette or early flowering stages of growth. In the 2002 to 2003 trial, control when dicamba + 2,4-D was used exceeded 90%, except when meadow knapweed was mowed at rosette and sprayed at early flowering (78% control). Mowing twice the previous year had only a slight effect on meadow knapweed (10% control). Grass biomass exceeded meadow knapweed biomass in all herbicide-treated plots. In the 2004 to 2005 trial, meadow knapweed control and grass biomass was maximized when plots were mowed at rosette and treated with dicamba + 2,4-D at early flowering or when treated twice with these herbicides; these were the only treatments where grass biomass exceeded meadow knapweed biomass. Nomenclature: Clopyralid, dicamba, glyphosate, imazapic, MCPP, triclopyr, 2,4-D, meadow knapweed, Centaurea debeauxii Gren. & Godr. CEDE5. Management Implications: Meadow knapweed is a nonrhizomatous perennial hybrid of black and brown knapweed in the plant family Asteraceae that has been introduced from Europe into many of the United States and Canadian provinces. It is not as widespread in North America as certain other Centaurea species, so herbicides have not been widely tested for efficacy on this hybrid. Therefore, two experiments were conducted to determine (1) whether meadow knapweed is similarly sensitive to several herbicides commonly used to control related knapweeds, (2) if herbicide application timing plays a role in control of meadow knapweed, and (3) whether mowing before, after, or instead of herbicide treatment can aid in meadow knapweed control. Herbicides were applied either in spring + autumn or in summer + autumn in the first experiment; in the second experiment, dicamba + 2,4-D was applied either before or after mowing and compared to one or two herbicide applications or two mowings. In the first experiment, clopyralid alone or in combination with other herbicides provided up to 100% control of meadow knapweed in the year following treatments. Triclopyr, dicamba, and glyphosate also resulted in control. These herbicides are often used at similar rates and timings to achieve control of other Centaurea species, which indicates that meadow knapweed is as susceptible to these products as other knapweeds. In the second experiment, combinations of mowing and herbicide applications at rosette or early flowering stages of growth generally reduced meadow knapweed biomass and increased grass biomass, although herbicide treatment alone achieved the same result. Mowing twice was an ineffective control strategy for this knapweed hybrid. Therefore, mowing is not recommended to augment control of meadow knapweed when using herbicides.

Efficacy of several herbicides on yellow archangel (Lamiastrum galeobdolon).

Abstract Yellow archangel is a twining perennial species that produces a dense evergreen canopy and may negatively affect forest floor vegetation. Because it is spreading rapidly in the Pacific Northwest (PNW), greenhouse and field trials were conducted on yellow archangel to determine its relative sensitivity to several herbicides. Products that slowed or prevented yellow archangel regrowth at 9 mo after treatment (MAT) in one or both iterations of the greenhouse trial were aminopyralid, diclobenil, glufosinate, imazapyr, isoxaben, metsulfuron, sulfometuron, triclopyr amine, and triclopyr ester + 2,4-D ester. In the field trial at 10 MAT, triclopyr and imazapyr were controlling 81 and 78% of treated yellow archangel, respectively, similar to aminopyralid, glyphosate, and metsulfuron (61 to 65%). Two applications of 20% acetic acid or 20% clove oil were controlling 53% at the same timing. At 13 MAT, only imazapyr and glyphosate were still providing good control of yellow archangel (81 and 80%, respectively), while all other products were controlling the weed at 53% or less. By 7 or 8 MAT after a second application, only imazapyr and glyphosate provided effective control of yellow archangel (86 to 94%). Nomenclature: 2,4-D, acetic acid, aminopyralid, clove oil, diclobenil, glufosinate, glyphosate, imazapyr, isoxaben, metsulfuron, sulfometuron, triclopyr, yellow archangel, Lamiastrum galeobdolon (L.) Ehrend. & Polatschek. Management Implications: Yellow archangel is a fast-growing and dense-canopied perennial species that is quickly becoming problematic along both coasts of the United States and Canada, and is particularly troublesome in forest, park, and ornamental settings in western Oregon, Washington, and British Columbia. Because the susceptibility of yellow archangel to herbicides is not known, greenhouse and field trials were conducted to determine which products could be useful for land managers to aid in its control. Herbicides identified in greenhouse trials that rapidly defoliated yellow archangel included diclobenil, glufosinate, isoxaben, metribuzin, triclopyr amine, and triclopyr ester + 2,4-D ester. Those products, in addition to aminopyralid, imazapyr, isoxaben, metsulfuron, and sulfometuron, effectively reduced yellow archangel regrowth at 9 mo after treatment (MAT) in one or both iterations of that trial. In the field, triclopyr amine, 20% acetic acid, and 20% clove oil quickly defoliated yellow archangel. However, control with acetic acid or clove oil had declined to only 53% at 10 MAT even after two applications. Control at 10 MAT with triclopyr and imazapyr was 81 and 78%, respectively, statistically similar to aminopyralid, glyphosate, and metsulfuron (61 to 65%). By 13 MAT, only imazapyr and glyphosate were still providing good control of yellow archangel (81 and 80%, respectively) and by 8 mo after a second application, control with these herbicides was 93 and 86%, respectively. Because yellow archangel seedlings were found in several of the treated plots, it is important to consider the seedbank when control programs for well-established patches are planned and conducted, and when maintaining the site following initial treatment.