Plant Bug Situation
Overall, we appear to be in good shape after the onslaught
of adult plant bugs that infested fields in June. Phone calls have slowed down
considerably, and most of the reports are that plant bugs are out there and in
some fields at damaging levels, but manageable. I think we have two big factors
that have helped us in this regard.
The first was our adult plant bug management. As we have
talked about a lot this year, our recommendation in Alabama is to treat a
threshold population of adult plant bugs, regardless of square retention. We
believe this helps to preserve square loss before it happens and reduces egg
lay. The immature populations in fields now are a result of this egg lay in June.
Allowing a threshold population of adults to “ride” a week to wait for square
loss gives them the chance to lay tens of thousands of eggs per acre over the following
7 days. Killing these adults before they have the chance to feed and lay eggs
has helped keep populations manageable.
The second thing that has helped us to this point is the use of
Diamond. When timed properly, Diamond provides residual suppression of plant
bug nymphs. While not in all cases, reports we have received seem to indicate
that following an application of Diamond + a knockdown insecticide, many fields
have bought themselves to the stink bug window (≈3rd week of bloom).
Stink Bug Situation
Speaking of stink bugs, reports of populations and damage in fields
are trickling in. Remember our threshold changes by week of bloom. Early bloom (weeks
1-2), threshold is 50-30% boll damage. Peak bloom (weeks 3-6), threshold is 10%
boll damage. Late bloom (weeks 7-8), threshold is 30-50% boll damage. Right
now, reports are that most of the populations are brown stink bugs. Typically, the
green species show up towards the end of July or first of August. In general,
pyrethroids aren’t as good on browns as organophosphates (Bidrin, acephate). However,
pyrethroids often do a good enough job on browns to keep populations below threshold.
Also consider your plant bug situation and resistance levels if needed to make
a bug complex spray.
Others
We have received several calls on aphids over the past week. In
most fields, populations are heavy in localized areas and are not a concern for
treatment. We don’t often recommend treating aphids, but some situations may require
an application, such as if cotton is drought stressed and/or late or if
populations are making scouting other insects, like plant bugs difficult. We
have gotten a report of the fungus killing aphids in the Wiregrass, so we
should expect populations to start crashing soon.
We have some pockets of spider mites in fields but overall we have
not gotten too many calls lately. Watch the weather and behind applications of
broad-spectrum insecticides for mites building.
We observed some bollworm egg lay in fields in central Alabama
this week, but we have not heard of any escapes in two or three-gene cotton.
Update on ThryvOn
I also wanted to give a quick update on some of the calls we are
getting with ThryvOn. ThryvOn provided excellent control of thrips in every
field we visited and based on all the feedback we received during the thrips window.
In June, when adults were migrating in, it was hard to see what ThryvOn was
doing. In many fields, populations were above threshold and square retention
was dropping. Some folks were frustrated with having to treat these fields
since it has a “plant bug trait.” However, we are now starting to realize some
of the benefits. We have gotten calls across the state reporting that
non-ThryvOn fields with similar planting dates and pre-bloom insecticide
regimes are being treated for immature plant bugs, while they cannot find many
nymphs or dirty bloom in the ThryvOn. This is what we hoped to get from this
technology in Alabama, “saving” a spray in July and pushing us to the stink bug
window.
Final Thoughts
We are off to a good start, but still have a long way to go. Keep
scouting and monitoring fields and be prepared to make timely applications when
needed. As always, if we can ever be of any help, or if you would like to
provide input on the situation in your area, please don’t hesitate to reach out
(Scott Graham: 662-809-3368; Ron Smith: 334-332-9501).
For more information on thresholds and insecticide
recommendations, visit the Alabama Cotton IPM Guide (IPM-0415). To
stay up-to-date on the Alabama cotton insect situation, subscribe to the
Alabama Cotton Shorts Newsletter,
Alabama Crops Report Newsletter,
and the Syngenta Pest Patrol Hotline.