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This is Jack Bacheler, extension entomologist at NCSU with the Wednesday cotton insect update. Today is July 25.
A high proportion of our cotton fields are presently in a time of maximum susceptibility for boll damage from brown and green stink bugs. Additionally, in many areas of the state this growing season we have moderate to high levels of stink bugs and quickly-developing attractive plants. I think that the potential for stink to cotton bolls is higher this year in NC than during the past few years, maybe even going back to 2004, our Year of the Stink Bug. Finally, we appear to have a high proportion of the harder to control brown stink bug in this year’s mix at this point.
Although our licensed independent crop consultants have a good handle on managing stink bugs, this year would be a good one for getting additional folks more active in examining approximately 1-inch diameter or quarter-sized bolls for internal damage, at least until we get beyond about the 6th week of bloom.
We are getting many questions about insecticide control options for stink bugs, particularly brown stink bugs. Bidrin and Bidrin containing combinations are very effective against brown stink bugs, rating a 5 on a 5 point rating system. However, we should all be reminded that the active ingredient dicrotophos is very toxic to humans and a 6-day reentry interval and appropriate safety safeguards must be observed. Also this material provides no caterpillar activity. Of the pyrethroids, bifenthrin (materials like Declare, Brigade and Discipline) rates a 4.3 out of a possible 5 for brown stink bug effectiveness while the other pyrethroids in general rate approximately 3.3. Adding acephate to a pyrethroid helps with brown stink bug control and lower rates of Bidin plus a pyrethroid is another effective option for stink bugs and provides bollworm control. If green stink bugs predominate, a number of insecticides, including pyrethroids, pyrethroid/chloronic combinations like Endigo, are effective. Do not use chloronics like Admire Pro, Centric, or Belay alone for stink bugs – members of this chemical class have ratings in the 1.5 to 3 range out of 5.
I would have been willing to place a substantial bet the our major bollworm moth flight from field corn would be extremely early this year based on our exceptionally high temperatures of this past spring and early summer. So far, the timing of our major flight appears to only a little ahead of schedule and is approximately half to two thirds up the state as of today. Our biggest 2/3-night light trap catch so far is has been 436 bollworm moths caught near Johns NC in Scotland County on July 23, not exceptional for this time of year at that location. This flight can be expected to extend into our remaining counties during the coming week and could still be on the large side. We should know more about the intensity of this flight by this time next week.
We have had one report this afternoon about relatively high levels of bollworm eggs being deposited on dried cotton blooms in Hyde County. Over at least the past 15 years or so, a greater proportion of bollworm eggs seem to be placed down on the canopy, especially on dried blooms. As most folks know by now, bollworm larvae are more likely to become established on the flower tissue of WideStrike and Bollgard 2 varieties than on other plant parts.
Adult kudzu bugs continue to flood into our soybean fields in southern NC. Thankfully, only low levels of nymphs are being produced so far. The high number of egg masses in some of these counties suggests that nymphal levels could increase sharply during the coming week. Remember to base insecticide sprays on the 15 nymphs per 15 sweep threshold taken away from field edges. Treating for adult kudzu bugs without nymphs only invites additional kudzu bug applications and greater odds of subsequent podworm and other caterpillar establishment.
That’s about it for this week. We’ll see you next Wednesday on August 1.