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Several selective and nonselective foliar-active herbicides were applied alone and in 1:l combinations as broadcast sprays in the spring for control of Drummond’s goldenweed on the Coastal Prairie of Texas. Picloram at 0.56 kg/ha or picloram plus 2,4,5-T, glyphosate, or atrazine plus paraquat at 1.12 kg/ha consistently controlled the weed. Atrazine and 2,4-D, applied singly or in combination at 1.12 to 2.24 kg/ha total herbicide, effectively controlled Drummond’s goldenweed only when soil-water content was high. Dicamba, like 2,4-D, was effective when applied in a “wet” year but not in a “dry” year. The effective herbicides controlled Drummond’s goldenweed for at least 3 years. Although Drummond’s goldenweed is morphologically similar to common goldenweed, it is apparently more susceptible to herbicides than its western counterpart. Drummond’s goldenweed [Isocoma drummondii (T. & G.) Greene] has traditionally been considered a minor component of vegetation of the southern Gulf Prairies and Marshes of Texas. However, during the past decade, it has become increasingly important and is now a significant weed problem on about 1 million ha of rangeland south and west of Corpus Christi. It also occurs as isolated stands in the eastern South Texas Plains, where a closely related species, common goldenweed [Isocoma coronopzyolia (Gray) Greene] has become a serious, widespread range management problem (Mayeux et al. 1979). Drummond’s goldenweed normally occurs as scattered individuals in the understory of woody plant communities on rangelands. However, upon removal of the brush cover, especially by mechanical methods which disturb the soil, goldenweed may develop dense stands and dominate range sites of moderate to high potential productivity (Mayeux and Scifres 1979). Drummond’s goldenweed is a heavily branched, suffrutescent subshrub with a rounded canopy which is usually 5 to 8 dm tall but may attain a height of 1 m. The leaves are linear and entire or occasionally with small marginal teeth, several centimeters long, and resinous. The flower heads are formed in late fall, are composed of 10 to 30 bright yellow disc florets only, and occur singly or in clusters of as many as 20 at the stem tips. The flowers produce pubescent achenes, 2 to 3 mm long, with a persistent pappus two to three times as long as the achene. A single plant may produce more than 200,000 achenes and new seedling density can exceed 2,600/ m2 (Mayeux and Scifres 1979). However, annual seedling mortality may range from 25 to lOO%, depending on site and rainfall during the year of emergence. Stem elongation rates of mature plants average 0.5 to 0.8 mm/day but may proceed at nearly 2 mm/day following rainfall during the growing season on Authors arc range scientist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Temple, Texas 76501, and professor, Department of Range Science, Texas A&M University, College Station 77843. The paper was approved by the Director, Texas Agricultural Experiment Station, as TA 15267. A part of the study was conducted while Mayeux was a graduate research assistant, Texas Agricultural Experiment Station, College Station 77843. The authors express their appreciation to Mr. Vernie Hubert of Vattman for providing the study area and to Julia Scifres for typing the manuscript. This paper reports the results of research only. Mention of a pest.icide in this paper does not constitute a recommendation by the USDA nor does It Imply registration under FIFRA. Manuscript received July 5, 1979. 98 well-drained sites which are not characterized by accumulations of salts and sodium. Since grazing of native grasslands provides the basis of the local economy of the area of Drummond’s goldenweed’s maximum adaptation, its spread, thickening of existing stands, and dominance of many sites following brush control have stimulated interest in its control. However, little information is available concerning the response of either Drummond’s or common goldenweed to conventional range weed control method. The problem is accentuated by confusion of Drummond’s goldenweed with common goldenweed or with “false broomweed” (Ericameriu austrotexana M.C. Johnston), formerly classified as Isocomapalmeri (Gray) Shinners and a common component of the south Texas perennial range weed complex. Mechanical methods which do not cause extensive soil disturbance, such as shredding, are not effective because Drummond’s goldenweed rapidly resprouts from lower stems and a woody caudex following top removal. Essentially no information exists concerning the response of Drummond’s goldenweed to herbicides. Common goldenweed, which occurs west of the geographical distributions of Drummond’s goldenweed, was controlled with 2,4-D [(2,4-dichlorophenoxy)acetic acid], picloram (4-amino3,5,6-trichloropicolinic acid), or a 1:l combination of picloram and 2,4,5-T[(2,4,5-trichlorophenoxy) acetic acid] applied as broadcast sprays in spring or fall if soil water content was adequate for rapid vegetative growth (Mayeux et al., 1979). Since control of common goldenweed with broadcast sprays depended on relatively high amounts of rainfall being received before treatment, responses among locations were erratic and relatively high herbicide rates were required for consistent control. However, forage species responded to goldenweed control with oven-dry standing crop increasing 5 to 10 kg/ ha for each 1% reduction in common goldenweed foliar cover. The objective of this study was to evaluate several herbicides and herbicide combinations for Drummond’s goldenweed control. Herbicides other than the phenoxy and related compounds commonly used on rangelands were included because highly susceptible agronomic crops such as cotton (Gossypium hirsutum L.) and vegetables are often grown on areas adjacent to rangeland infested with Drummond’s goldenweed. Glyphosate [N(phosphonomethyl)glycine] has proven effective for control of several species of perennial weeds on pastures (Johnson 1976) and railroad rights-of-way (Andrews et al. 1974). Glyphosate has also been used successfully for control of perennial range weeds such as Carolina horsenettle (Solanum carolinense L.) (Banks and Santelmann 1976) and African rue (Peganum harm& L.) (Allen and McCully 1976). Atrazine [2-chloro-4-(ethylamino)-6(isopropylamino)-s-triazine] is used on western rangelands to control weedy grasses and herbaceous broadleaf species (Houston and van der Sluijs 1973) especially in conjunction with grass seedings (Eckert et al. 1974). It also effectively controls silverleaf nightshade (Solunum eleugnifokum Cav.) (Johnson et al. 1976) and Canada thistle [Cirsium arvense (L.) Stop.] (Carson and Bandeen 1975, Parochetti 1974), and partially controls green rabbitbrush [Chrysothamnus viscidiflorus (Hook) Nutt.] when applied at 1 kg/ha JOURNAL OF RANGE MANAGEMENT 34(2), March 1981 (Evans and Young 1972). The contact herbicide paraquat (1,1’dimethyl-4,4’-bipyridinium ion) was evaluated because of its effectiveness against phenoxy-resistant range weeds such as geyer larkspur (Delphinium geyeri Green) (Hyder 1972). Table 1. Environmental conditiom daring herbicide applicationa to Drammondb goldenneed on June 4.1975, and May 26,1976, near Kingsville, Texas. |
