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This research examined a potential nuisance aspect of the use of the volatility-reducing agent (VRA) potassium carbonate when combined with glyphosate in spray-tank mixtures. A VRA is now required to be added to dicamba applications to reduce off-target movement from volatility. When no VRA potassium carbonate was added to the spray mixture, there was no pressure buildup. The addition of VRA potassium carbonate plus glyphosate (which lowers the pH) resulted in an observed pressure buildup. Although the gas produced was not identified, it would be expected to be carbon dioxide formed by the dissolution of the carbonate anion from the VRA. Source water pH range from 3.2 to 8.2 had no effect on pressure buildup. Pressure buildup was directly related to water temperature, with a linear response to temperature when the VRA was added last; in contrast, a less direct relationship of temperature to pressure buildup existed at temperatures >30 C when the VRA potassium carbonate was added first. There was no effect on the pressure increase from adding a defoamer or a drift control agent.
Dioscorea oppositifolia (Chinese yam) is an exotic perennial vine invading natural areas in the temperate regions of the eastern United States. Rapid early-season growth of D. oppositifolia is facilitated by an extensive tuber system. Plants can reach heights greater than 370 cm, as the plants climb trees and other vegetation. Shoot length increased 3.6 cm/d from late May to mid-August under field conditions, and primary and secondary tuber length increased 0.28 and 0.2 cm/d, respectively. This indicated rapid vegetative growth and substantial food reserves to form new plants in subsequent years. Dioscorea oppositifolia plants also formed aerial bulbils of 0.8- to 1.2-cm diameter, which are important in dissemination of the species over geographical areas. A field study indicated incomplete control from manual removal, clipping by hand, or glyphosate (2% v/v) application to control D. oppositifolia, although glyphosate was the most effective. Additionally, the use of herbicides was more efficient from a time-utilization perspective than either manual removal or clipping. In a separate study, glyphosate application at flowering was more effective in reducing D. oppositifolia growth the year after application as compared with glyphosate applications soon after emergence. Under greenhouse conditions, however, glyphosate at 0.84 kg ae/ha provided <15% control. The ester formulation of triclopyr at 2.5 kg ai/ha provided >90% D. oppositifolia control. Metsulfuron provided 31% control, and mesotrione provided 36% control and at higher rates may reduce D. oppositifolia growth. Several other herbicides having diverse modes of action provided minimal control of D. oppositifolia.
Herbicide treatments (4:1 ratio of 2,4-D amine:picloram) at 0.7 and 1.4 kg ae/ha at early postemergence (10- to 15-cm horsenettle height), midpostemergence (early flower), and late postemergence (fruit initiation) applied both early and late in the growing season provided >80% horsenettle control. Horsenettle density at season's end in all treated plots was less than 0.25 stems/m2, whereas untreated plots contained about 5 stems/m2. Horsenettle control the next spring was between 47 and 66% for all rates and application timings, and horsenettle density in treated plots was less than 3 stems/m2 as opposed to about 6 stems/m2 in the untreated plots. Clover drilled into the treated area the year after herbicide application was injured, indicating clover establishment the season after application of this package mixture would be difficult.
Chinese yam is an exotic perennial vine that invades natural areas in the temperate regions of the eastern United States. Research was conducted from 2001 to 2004 to evaluate growth, reproduction, and management options for this weed. Vine length, lateral shoot production, and reproductive capacity were lower in the first year of growth compared to 2 subsequent years. During the second and third growing season, plants were more mature and tended to flower earlier and produce larger bulbils compared to the first growing season. Maximum vine length was not reached prior to frost in the first year and was approximately 480 cm in each of the subsequent years. Both glyphosate and triclopyr were effective in controlling plants growing from bulbils and plants growing from tubers. Triclopyr did not display acropetal translocation, in that only the treated tissue died. However, both products displayed excellent basipetal translocation resulting in elimination of tubers and no shoot regrowth the year following treatment. Native area managers should attempt to eradicate small populations of Chinese yam prior to establishment of an extensive tuber system.
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