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This is Jack Bacheler, Extension Entomologist at NCSU with the weekly insect update. Today is Wednesday, July 11.
Although covering other pests briefly, this week we’ll focus on stink bugs and their management in cotton. Recent better rainfall patterns and already moderate to high levels of stink bugs could indicate that these pests will soon infest cotton fields at greater levels than in recent years here in NC.
Stink bug scouting procedures and thresholds are well defined in the Southeast. By using the dynamic threshold, producers and consultants can focus on times during the bloom period when cotton is most susceptible to yield-reducing boll damage. Scouting for stink bug damage has been made much more efficient through the use of the Stink Bug Decision Aid Field Card. This card lists the internal boll damage thresholds by week of bloom, provides straightforward scouting steps, has a template for selecting the correct size boll and has images of internal stink bug damage. The cards are available at both our cotton scouting school to be held in the next few weeks and also can be viewed at our Cotton Insect Corner web site under “What’s New”. In a nutshell, cotton is particularly susceptible to boll damage during weeks 3 through 5 of the bloom period. During this time, we recommend that producers use a protective threshold of 10% internal damage to bolls. Thresholds before and after this 3-week window are higher, indicating that higher damage levels to quarter-sized bolls can tolerated during periods of fewer susceptible bolls. Count both inner boll wall surface warts and any stained lint as a damaged boll, even if this damage is slight.
With most areas of the state receiving significant rainfall this week, we hope that our building mite levels will drop. Also, where cotton aphid outbreaks are present, at least plant stress should also be down significantly due to good moisture levels, which fortunately also lowers the potential yield loss due to aphid feeding. If past years are a guide, the aphid fungus is more likely as mid to late July approaches, so this pathogen should also help with cotton aphids in the coming weeks.
We have received several calls of upper square retention dropping to the 70 to 80% range, though in very widely scattered cotton fields. In these cases, the middle and lower square retention was good to excellent and subsequent sweep net samples have been well under the protective threshold of 8 plant bugs per 100 sweeps. In most fields, square retention remains high, often in the 95% range.
Based on the development of kudzu bugs on kudzu and in some cases on early planted soybean, the first field generation of adults should now be moving into to soybeans, with kudzu bugs showing up both in greater numbers and in soybean acreage not previously infested. We expect this adult migration into soybean to increase during at least the next 2 to 3 weeks. In prioritizing soybean fields for scouting, expect earlier planted soybean fields to harbor higher numbers of kudzu bugs. The suggested treatment threshold for kudzu bugs is 15 nymphs per 15 sweeps averaged over 6 to 8 locations at least 50 feet in from field edges. Treating for adult kudzu bugs or fewer than the recommended number of nymphs increases the odds of multiple insecticide applications without a yield benefit. Unneeded multiple applications for kudzu bug also increase the probability of a subsequent establishment of various caterpillar pests such as podworms, tobacco budworms, loopers and armyworms.
With the cotton and soybean insect scene certain to become more interesting in the coming weeks, we’ll report again next Wednesday on July 18. See you then.