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This is Jack Bacheler again, Extension Entomologist at North Carolina State University with the weekly cotton and soybean update. Today is Thursday, August 16.
Our major point of emphasis during the next 3 to 4 weeks will that major moth flights will be increasingly attracted to later, bigger ranker cotton fields with more immature bolls and to open-canopied, flowering soybean plants. The same trend should unfold with stink bugs and cotton, though stink bugs will tend to be more attracted to soybean fields during pod fill. In the case of kudzu bugs, the highest levels still appear in taller earlier planted fields while late planted beans, especially following wheat, seem to have lower levels of kudzu bugs.
We now have a number of cotton fields which are cutting out to the point of being unattractive to both stink bugs and bollworms. This is a two-edged sword, however. On the plus side, the unattractive fields are also becoming an increasing challenge for caterpillars and stink bugs to damage. On the minus side, both bollworm moths and stink bugs readily fly to later maturing cotton fields that are still susceptible to damage. These late fields can harbor significant concentrations of insects, even when the general overall populations are low to moderate. In some areas, however, we expect earworm moths and stink bug levels to be high throughout a wide range during the next three weeks or so.
In cotton fields that have been blooming for 8 weeks or more, the stink bug internal damage treatment threshold is at least 50%. So even though we still recommend assessing quarter-sized bolls for damage, most bolls on these plants are no longer susceptible to stink bug injury.
As was the case in 2010 and in 2011, we appear to be experiencing a larger flight of August to mid-September earworm moths than was the case with our earlier so-called major flight. As of today, this late flight has been ongoing in Scotland County for approximately a week, with a 3-day light trap count of almost 500 moths this past Monday. This is the highest light trap count of so far this year. By this coming week, expect higher levels of these earworms in many cotton and soybean fields throughout the state. Another complicating management factor is that tobacco budworms are being found in both soybean and peanut fields, making control with pyrethroids ineffective in these situations. I looked at a worm sample from a peanut field last week that was 60% tobacco budworms. Additionally, remember also that 1) some populations of podworms show some pyrethroid tolerance or the ability to survive pyrethroids and that 2) pyrethroids do not provide acceptable control of loopers and beet and fall armyworms. Therefore, we now recommend that producers consider either using a pyrethroid alternative such as Belt, Steward or Tracer (Blackhawk) or a pyrethroid combination, such as a pyrethroid plus one of the aforementioned caterpillar materials. However remember that Belt, Steward and Blackhawk alone do not provide adequate control of stink bugs.
I have been in several soybean fields during the past week in which the levels of kudzu bug adults and nymphs were many times the suggested threshold of 15 nymphs per 15 sweeps around the perimeter. In all but 2 of 8 cases, sweeps taken from field interiors had sub-threshold levels of nymphs. We also realize that visual observations of kudzu bug nymphs and adults reveal many more kudzu bugs than with sweeping. However, the above presently-suggested threshold was based on sweep net sampling which is undertaken not to obtain all of the nymphs on a plant, but to obtain a sub-sample of nymphs that indicate a treatable population. Although changing weekly in the direction more soybean fields requiring treatment, treatment has not been justified in the vast majority of our soybean fields at this point. Growers are again urged to observe patience with moderate to high adult levels and instead concentrate on fining threshold levels of nymphs in field interiors.
With the insect scene changing from week to week, we’ll report again next Wednesday on August 22. See you then.