RALEIGH, N.C. — With low cotton prices, growers are rightly looking to reduce the cost of production. This previous article details why growers should not skimp on mite and insect pest management. This article details why, using tarnished plant bug as an example.
These are trials testing various thresholds, when we should start and stop treatments, and ThryvOn efficacy for tarnished plant bug. For all these graphs, All the dollar amount is net profit or losses relative to the untreated. The letters represent mean separations. If treatments share the same letter, then the yields are not significantly different. The number at the bottom of the bars is number of insecticide applications.
Net profit or losses were calculated based on cotton that was $0.78 to $0.82 per lb. Of course, with today’s low prices, the economic gain of spraying is less over the check, but it’s still usually very positive.
WOB = week of bloom
WOS = week of squaring
We initiated treatments at different times and kept spraying automatically, except in the threshold treatments (note that there were two separate economic threshold treatments). This trial demonstrates the value of using the economic threshold for tarnished plant bug.
WOB = week of bloom WOS = week of squaring We initiated treatments at different times and kept spraying automatically in two different planting dates, except in the threshold treatments (note that there were two separate economic threshold treatments). This trial demonstrates the value of using the economic threshold for tarnished plant bug.
Standard = two mid-season calendar sprays
High threshold = 12 per 100 sweeps pre-bloom (didn’t use square retention) or 3.5 on drop cloth post-bloom
Extension Threshold = extension-based threshold
Rotation = extension threshold + rotating modes of action of insecticides
Short Interval = extension threshold + rotating modes of action of insecticides + using a 3-4 day application window rather than 7
Novaluron = extension threshold + rotating modes of action of insecticides + using a 3-4 day application window rather than 7 + using Diamond
Low N = extension threshold + rotating modes of action of insecticides + using a 3-4 day application window rather than 7 + using Diamond + lower rate of nitrogen
This trial demonstrates that we can add IPM principles into tarnished plant bug management without sacrificing yield. Note that the spray numbers are fractions because these numbers are averaged over a 2 year study.
Midsouth growers that deal with tarnished plant bug often apply novaluron (Diamond) at third week of squaring. This slows down development about the time that adult migrations have finished in their region. We trialed this approach in North Carolina (first spray before threshold). We did not hit threshold until the next week. At that time, we put out our other insecticide regimes (first spray at threshold). This demonstrates the value of waiting to hit threshold before applying. Note that we had two check treatments in this trial.
This trial demonstrates the value that ThryvOn can bring even under low pressure. Note that we hit threshold twice on the non-ThryvOn variety, but only once on the ThryvOn variety.
WOB = week of bloom
We initiated treatments at different times and then kept spraying automatically once we started. We did not have a threshold treatment in this trial. This demonstrates the value that ThryvOn has, but also that it must be protected if plant bugs are present above threshold.
Some states in the Midsouth are increasing thresholds for ThryvOn cotton (2x threshold). This trial shows that our tarnished plant bug thresholds should remain the same for ThryvOn and non-ThryvOn cotton.
In conclusion, tarnished plant bug must be treated to preserve yield if the economic threshold is reached.
— Dominic Reisig, N.C. State University
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