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Author: McNaughton, Kristen E.
Department: Department of Plant Agriculture
Program: Plant Agriculture
Advisor: Robinson, Darren
Abstract: Field studies were conducted in Ridgetown, Ontario from 2008-2010 on processing tomato (Solanum lycopersicum L.) to determine if various drift rates of either glyphosate or bromoxynil followed by an in-crop 250 g ai ha-1 metribuzin application, applied 3-4 days later, would result in cumulative herbicide stress. Greenhouse and growth room experiments further examined cumulative herbicide injury when drift rates of glyphosate were followed by metribuzin when tomato was grown under moisture-limiting and –non-limiting conditions. Differences in glyphosate uptake and translocation when followed with metribuzin, under both moisture-limited and –non-limited conditions, were examined. A transient synergistic interaction was observed when 22.5 g ae ha-1 glyphosate was followed by metribuzin in the field; however, by 28 days after the metribuzin application (DAT-B) all responses were additive. Also, all dry biomass and yield ratings when 45, 90, and 180 g ae ha-1 glyphosate was followed by metribuzin were additive. However, a drift rate of 22.5 g ae ha-1 glyphosate alone (2.5% of the recommended glyphosate field rate) caused a 23% decrease in red tomato yield. Simulated drift rates of 8.5, 17, and 34 g ai ha-1 bromoxynil followed by metribuzin had transient synergistic responses at the 7 DAT-B injury rating, but by 28 DAT-B all responses were additive. A synergistic interaction observed during initial visible injury ratings persisted to yield when 68 g ai ha-1 bromoxynil (20% of the recommended bromoxynil field rate) was followed by metribuzin. At yield, 50 T ha-1 of red tomato was expected, based on Colby’s equation, but only 36 T ha-1 was observed. This finding indicates that a cumulative herbicide interaction can occur even if the various herbicides are applied up to 4 days apart. Growth room and green house experiments also supported the general finding that drift rates of glyphosate followed by metribuzin are examples of additive herbicide interactions, regardless of drought stress. Visible glyphosate injury was more pronounced when tomato were grown under adequate moisture; however, plants treated with glyphosate and grown under moisture-limited conditions were shorter and initiated flowering up to a week later. Contrast analysis indicated that moisture levels affected glyphosate visible injury and height ratings up to 21 DAT-B. Visible injury tended to increase with increasing glyphosate drift rates. Glyphosate uptake studies supported the observation of transient synergism when glyphosate was followed by metribuzin. When 45 g ae ha-1 [14C] glyphosate followed by metribuzin was applied to tomatoes grown under moisture-limited conditions, the percentage of applied 14C absorbed by the plant and retained in the treated leaf increased 24 hours after metribuzin (HAT-B) application. The increase was temporary and by 96 HAT-B there was no difference in absorption or translocation between plants treated with glyphosate alone or followed by metribuzin. Interestingly, a spike in 14C absorption and translocation was observed at 24 HAT-B for moisture-limited plants treated with either 45 or 90 g ae ha-1 [14C] glyphosate alone or 45 g ae ha-1 [14C] glyphosate followed by metribuzin. The increase in absorption and translocation corresponded to the resumption of watering, indicating that if drought conditions are reversed, up to 4 days after glyphosate drift, then the stressed plant may be able to absorb additional glyphosate several days after the drift event.
Date: 2013-10
Rights: Attribution-NonCommercial-NoDerivs 2.5 Canada

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Attribution-NonCommercial-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 2.5 Canada