Abstract: Combinations of 0 to 1,120 g ae/ha 2,4-D plus 0 to 42 g ai/ha metsulfuron were evaluated in both field and greenhouse experiments. Addition of metsulfuron to 2,4-D increased Virginia buttonweed (Diodia virginiana) fresh weight reduction in the greenhouse compared with 2,4-D alone, but reduction in fresh weight was not different from 32 g/ha or more of metsulfuron applied alone. In field experiments 5 wk after treatment (WAT), combinations of metsulfuron and 2,4-D did not control Virginia buttonweed greater than 32 g/ha or more of metsulfuron alone. No synergism for the combinations was observed. Field experiments conducted from 1991 to 1993 evaluated three-way combinations of herbicides for Virginia buttonweed control. Treatments included: 2,4-D plus mecoprop plus dicamba (five herbicide premixes), 2,4-D plus dichlorprop plus dicamba, 2,4-D plus MCPA plus dichlorprop, mecoprop plus MCPA plus dichlorprop, or 2,4-D plus mecoprop plus dichlorprop. Combinations containing at least 688 g/ha 2,4-D provided the most consistent Virginia buttonweed control 2 WAT. By 7 WAT, control was no more than 60% for any treatment. A separate experiment evaluated the effects of repeated applications of two- or three-way herbicide mixtures applied at least 5 wk apart when ground cover regrowth was 25%. Treatments included: 2,4-D plus dichlorprop plus dicamba ester, 2,4-D plus mecoprop plus dicamba amine, 2,4-D plus dichlorprop amine, or 2,4-D plus dichlorprop ester. Ground cover 1 yr following application of sequential treatments was 35% or less compared to 65% in the nontreated control. Following 2 yr of herbicide application, ground cover in the treated plots was 28% or less.
Nomenclature: 2,4-D, (2,4-dichlorophenoxy)acetic acid; dicamba, 3,6-dichloro-2-methoxybenzoic acid; dichlorprop, (±)-2-(2,4-dichlorophenoxy)propanoic acid; MCPA, (4-chloro-2-methylphenoxy)acetic acid; mecoprop, (±)-2-(4-chloro-2-methylphenoxy)propanoic acid; metsulfuron, 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid; Virginia buttonweed, Diodia virginiana (L.) #3 DIQVI.
Additional index words: 2,4-D, dicamba, dichlorprop, mecoprop, MCPA, metsulfuron, DIQVI.
Abbreviations: DMA, dimethylamine; IOE, isooctyl ester; WAT, weeks after treatment.
