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Tarnished Plant Bugs in Cotton

We’ve been receiving some questions about tarnished plant bugs over the last few days. Here is some good information from Dr. Phillip Roberts.

Unlike cotton production areas in the Mid-South, tarnished plant bug is an uncommon and sporadic pest of Georgia cotton.  However, tarnished plant bug populations have been higher than normal and more insecticide applications have targeted tarnished plant bugs than usual during 2014.  Recently we have received reports of immature tarnished plant bugs in some fields; this is rarely observed in Georgia cotton.

Our primary method for scouting plant bugs is square retention.  Our goal is to retain 80 percent of all first positions as we enter bloom.  The square retention technique works well in pre-bloom cotton but is not as a reliable technique in blooming cotton as physiological shed confounds counts.

More scouts are using sweep nets to monitor plant bugs.  Sweep nets are an excellent tool for monitoring adult plant bug populations, but the drop cloth (especially a black drop cloth) is more effective for monitoring immature plant bugs.

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Adult tarnished plant bug (left) and immature tarnished plant bug in bloom (right).  Images by Russ Ottens, University of Georgia and Ron Smith, Auburn University, Bugwood.org.

Effective use of the sweep net becomes difficult after bloom due in part to plant size and more emphasis should be placed on use of a drop cloth.  Also be observant for both adult and immature plant bugs when making visual plant inspections; examine terminals and inside the bracts of squares, blooms, and small bolls.  Also be observant for “dirty blooms”, blooms in which many of the anthers are dried and brown.  Dirty blooms are an indication that plant bug (especially nymphs) are feeding on larger squares which the plant did not shed.

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“Dirty Blooms”.  Images by Ron Smith and Barry Freeman, Auburn University, Bugwood.org.

We have also observed clouded plant bugs, especially west of I-75.  Clouded plant bugs will feed on squares similar to tarnished plant bugs but will also more readily feed on small bolls.

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Clouded plant bug adult (left) and immature (right).  Images by Ron Smith, Auburn University, Bugwood.org.

We do not have recommended thresholds for use of drop cloths, visual inspections, or sweep nets in Georgia.  However, entomologist in the Mid-South have developed solid workable thresholds when using these sampling techniques which should be applicable to Georgia cotton.

Mid-South Plant Bug Thresholds: Tarnished plant bug thresholds can be used for clouded plant bugs, but clouded plant bugs should be counted 1.5 times when using a sweep net. Note that the threshold is higher during the third week squaring and bloom compared with the first two weeks of squaring.

Third week of squaring through bloom: Drop Cloth: 3 plant bugs/6 row feet, Visual: 10 plant bugs/100 plants, Sweep Net: 15 plant bugs/100 sweeps

First 2 weeks of squaring: Drop Cloth: 1 plant bug/6 row feet, Visual: 5 plant bugs/100 terminals, Sweep Net: 8 plant bugs/100 sweeps