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Richard G. Greenland and Kirk A. Howatt

Nightshade species are difficult to control in tomato production and their interference reduces both tomato yield and quality. Rimsulfuron can be used to control nightshades, but species and biotypes vary in their response to rimsulfuron. The objectives of this study were to evaluate control of hairy nightshade (Solanum sarrachoides Sendt.) and eastern black nightshade (Solanum ptycanthum Dun.) by rimsulfuron and compare North Dakota eastern black nightshade accession response to three acetolactate synthase (ALS)-inhibitor herbicides. In field studies conducted at Oakes, N. Dak., rimsulfuron at rates of 26 or 53 g·ha–1 a.i. was applied within 1 week after transplanting tomato (EPOST) or 2 to 4 weeks after transplanting (POST). Rimsulfuron gave excellent control of hairy nightshade when applied POST, and poor to excellent control when applied EPOST, with control being much better when hairy nightshade had emerged before the EPOST application. Rimsulfuron at 53 g·ha–1 provided greater control than at 26 g·ha–1 only for the EPOST applications. Rimsulfuron controlled hairy nightshade which allowed eastern black nightshade (which was not controlled by rimsulfuron) to dominate tomato. Tomato yield was lower when dominated by hairy nightshade than by eastern black nightshade. This was due to the earlier emergence and faster growth of hairy nightshade compared to eastern black nightshade. Tomato yield was higher in the hand-weeded check than for all other treatments in 1999, the only year the hand-weeded check was included in the study. Greenhouse studies on plants grown from seed collected at the experimental site verified that eastern black nightshade was tolerant to rimsulfuron but was controlled by tribenuron and imazethapyr. Rimsulfuron can be used in tomato production to control hairy nightshade, but not the accession of eastern black nightshade found in this study. Chemical names used: N-((4,6-dimethoxypyrimidin-2-yl)aminocarbonyl)-3-(ethylsulfonyl)-2-pyridinesulfonamide (rimsulfuron); (α,α,α-trifluoro-2,6-dinitro-N,N dipropyl-p-toluidine) (trifluralin); methyl 2-[[[[(4-methoxy-6-methyl–1,3,5-triazin-2-yl)methylamino]carbonyl]amino]sulfonyl]benzoate (tribenuron methyl); (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo–1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid (imazethapyr).

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Lijuan Xie, Deying Li, Wenjuan Fang, and Kirk Howatt

Selective control of creeping bentgrass (Agrostis stolonifera) is desirable when it has escaped into other turfgrasses. The objective of this study was to evaluate the influence on creeping bentgrass control from adding urea ammonium nitrate (UAN) to mesotrione plus non-ionic surfactant (NIS) spray solution, and raking to remove dead tissues of creeping bentgrass. A 2-year field study was conducted with a split-plot design, where raking was the whole plot treatment and herbicide was the sub-plot treatment. Herbicide treatments included application of mesotrione at 56 and 70 g·ha−1 singly and sequentially with 0.25% (v/v) NIS or 0.25% (v/v) NIS plus 2.5% (v/v) UAN solution. Sequential applications were made three times on a 2-week interval. Removing the dead clippings by raking improved the creeping bentgrass control from 60% to 73% averaged over rates, timings, adjuvants, and years. Adding UAN to NIS plus mesotrione improved creeping bentgrass control from 78% to 98% with three sequential applications at 70 g·ha−1.