Response of Processing Tomato to Simulated Bromoxynil Drift Followed by In-Crop Metribuzin Application

Abstract

Simulated drift rates of bromoxynil followed by an in-crop application of metribuzin were applied to processing tomato in eight field studies conducted from 2008 to 2010 in Ridgetown, Ontario, Canada, to determine if a synergistic interaction occurred due to the cumulative herbicide application. A transient synergistic response was observed 7 d after treatment (DAT) when bromoxynil drift rates of 8.5, 17, and 34 g ai ha−1were followed 3 to 5 d later by metribuzin at 250 g ai ha−1. By 28 DAT, visible injury ratings were additive for 8.5, 17, and 34 g ha−1bromoxynil followed by metribuzin treatments. However, when bromoxynil at 68 g ha−1(20% of field rate) was followed by metribuzin, a synergistic interaction was evident and remained through harvest. Based on Colby's equation there was greater visible injury than expected at 7, 14, and 28 DAT when bromoxynil at 68 g ha−1was followed by metribuzin. A corresponding synergistic reduction of plant dry weight and marketable tomato yield, compared with the nontreated control, was identified. Marketable yields were expected to be 65% of the control according to Colby's equation, but observed yield reductions were 49% when bromoxynil at 68 g ha−1was followed by metribuzin. In general, tomato plants sprayed with metribuzin after bromoxynil drift had greater injury than treatments sprayed with bromoxynil alone.