The effectiveness of dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), and triclopyr [(3,5-6-trichloro-2-pyridinyl)oxy]acetic acid and mixtures of these herbicides with 2,4-D [(2,4-dichlorophenoxy)acetic acid] for the control of horsenettle (Solanum carolinenseL.) in Kentucky bluegrass (Poa pratensisL.) pastures was evaluated at three different field sites in Southwest Virginia over a period of 3 yr. Picloram applied at 0.6 and 1.1 kg/ha significantly reduced horsenettle roots, as indicated by a 98% reduction in shoots 1 yr after the first annual application. No shoots emerged within 18 months after three annual picloram applications. There was no significant difference between picloram applied alone and in a mixture with 1.1 kg/ha of 2,4-D. Three annual applications of triclopyr at 3.4 kg/ha reduced horsenettle shoots from 82% to 92%. The 3.4-kg/ha rate of triclopyr was slightly more effective in controlling horsenettle roots than was triclopyr at 1.7 kg/ha alone and in mixture with 1.1 kg/ha of 2,4-D. Dicamba at 0.6 and 1.1 kg/ha reduced the horsenettle shoots by 74% and 81%, respectively. The reduction was similar from mixtures of dicamba (0.1 and 0.3 kg/ha) with 2,4-D (0.4 and 0.8 kg/ha). There were no effects on the bluegrass forage that could be attributed to the herbicides.
Dinitroaniline herbicides are major herbicides used to control annual grass weeds in cool-season turfgrasses. At least three herbicides, benefin, pendimethalin, and trifluralin are labeled preemergence to control weeds in established turfgrass. Prodiamine could be a competitive product. Benefin at 2.2 to 3.4 kg ai/ha, pendimethalin at 1.7 to 3.4 kg ai/ha, prodiamine at 0.6 to 1.7 kg ai/ ha, and benefin plus trifluralin at 1.1 plus 0.6 to 2.3 plus 1.1 kg ai/ha effectively control many annual grass weeds, including large and smooth crabgrass, yellow and green foxtail, barnyardgrass, goosegrass, fall panicum, and annual bluegrass. Most dinitroaniline herbicides provide residual preemergence weed control for the entire growing season. In general, Kentucky bluegrass, perennial ryegrass, tall fescue, red fescue, and other cool-season turfgrasses tolerate most of these herbicides, although higher-than-normal rates of any dinitroaniline herbicide could restrict root growth and cause stand thinning in turfgrass species.
Four field locations were used to compare environmental factors on efficacy of four postemergence grass herbicides in Kentucky bluegrass and bermudagrass turf. Imazaquin, BAS 514, and tridiphane were compared to fenoxaprop-ethyl, a registered herbicide, for postemergence control of large crabgrass. Best large crabgrass control was provided by BAS 514 and fenoxaprop-ethyl. Use of BAS 514 gave equal turf quality, phytotoxicity to the turf, large crabgrass control, and stand compared to fenoxaprop-ethyl. Imazaquin and tridiphane reduced turf quality and were phytotoxic to both turf types, and did not control large crabgrass adequately.
DCPA, bensulide, and diphenamid gave preemergence control of annual bluegrass in freshly tilled soil. Overseeding bermudagrass golf greens with cool season grasses reduced through competition the amount of annual bluegrass cover and provided a desirable putting surface. Annual ryegrass was more effective in this respect than red fescue. Bensulide and DCPA gave control of annual bluegrass and the rates required were partially offset by competing cool season grasses. The cool season grasses seeded one month after treatment were not affected by 5.6 kg/ha of bensulide whereas higher rates gave significant reductions in ground cover with cool season grasses. The margin of safety was not as great with diphenamid. Although bermudagrass growth was retarded in spring with the overseeded cool season grasses, the turf quality was maintained better with the transition from the overseeded grasses to bermudagrass than from the infested annual bluegrass to bermudagrass. Plant competition reduced the number of tillers and weight of annual bluegrass plants in the field and greenhouse studies.
Greenhouse studies were conducted to determine the extent of translocation from the foliage to fleshy roots, the inherent toxicity, and the fate of radiolabeled and nonlabeled dicamba, picloram, and triclopyr in horsenettle. Roots of horsenettle acted as the major sink for photosynthate accumulation at the 0.2- to 0.5-bloom growth stages as determined by autoradiography. Dicamba, picloram, and triclopyr were translocated into the roots of horsenettle and accumulation continued for at least 16 days.14C associated with each herbicide found in the roots ranged from 1.3% at 4 days to 3.8% at 16 days. After 16 days, slightly more14C from plants treated with dicamba and triclopyr (3.8 and 3.6%) than picloram (3.0%) was translocated to roots. These compounds were metabolized slowly in the foliage and roots as determined by thin-layer chromatography (TLC) and autoradiography. In translocation studies with horsenettle shoots, picloram at 1.12 kg/ha killed the treated and untreated shoots and roots. Dicamba and triclopyr at the highest rates killed the treated shoots and partially destroyed the root system. Symptoms were noted on the untreated shoots, but full recovery occurred at 8 weeks. Since each of the herbicides was metabolized slowly and only slight differences in their translocation were observed, the relatively higher herbicidal effectiveness of picloram must be attributed to its greater inherent potency.
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