Overall, the cotton insect situation has been quiet this year., which is not unexpected considering how planting season went. Acres will be down significantly this year, how much? We will have to wait to see. Hopefully we will quickly turn into a “normal” summer pattern with scattered (and hopefully timely) storms for the rest of the year.
For the first time in my career, I am getting calls about
thrips and plant bugs at the same time (and on top of that, plant bug calls are
later than usual too). Plant bugs have been sporadic with most reports being
that few are detected in fields. However, we have also received reports of populations
well above threshold and square retention in the 65% range. This highlights the
importance of scouting and not guessing where plant bugs are (or are not).
This year, as much as any, we cannot afford to allow square
retention to fall below threshold, but we also need to manage plant bugs as economically
(cheap) as possible. However, achieving adequate control is still our primary
goal. Remember, the best way to maximize the return on an insecticide
application is to apply it ON TIME. The only way to do this is to scout fields
and follow economic thresholds. In pre-bloom cotton, threshold is 8 adult plant
bugs per 100 sweeps AND to maintain 80% square retention (note: in late planted
cotton, we may want to be more aggressive on square retention to promote
earliness).
With that in mind, we have a few options for control of
adults in pre-bloom cotton:
1.
Imidacloprid: Many trade names.
Imidacloprid is the most economical option we have for plant bug control. While
imidacloprid does not provide 100% control (closer to 60-65%) at the highest
labeled rates, it generally provides enough to get populations under threshold and
preserves square retention
2.
Thiamethoxam: Centric, Hub WDG.
Thiamethoxam is another neonicotinoid that provides good control of adult plant
bugs. Our general recommendation is 2 oz/A. While a little more costly than
imidacloprid, this material provides better control. Another option is Endigo
ZCX, which is a premix of Centric (thiamethoxam) and lambda-cy. Endigo ZCX at
3.5 oz/A provides the equivalent rate of Centric (2 oz/A) and lambda-cy (1.5
oz/A). While the added lambda-cy may be more likely to flare mites, this
pre-mix may be a little more economical than Centric alone.
3.
Sulfoxaflor: Transform (1.5 oz/A)
provides the best control of plant bugs of all currently registered materials. For
that reason, we like to wait to use it when immature plant bugs are present.
Waiting for Transform can help to delay resistance and manage adults more
economically.
4.
Other options: Acephate (0.5 lb) or pyrethroids
(highest labeled rate) are options for adults but are not generally recommended.
The reason for this is multi-fold. 1. Resistance management. We prefer to use
neonics (imidacloprid or thiamethoxam) on adults and then switch to the “harder”
chemicals (Ops/pyrethroids) after bloom when targeting immature plant bugs
and/or stink bugs. 2. These classes of chemicals tend to be harsher on
beneficials, which could lead to outbreaks of spider mite (however, we can and
have flared spider mites with neonics sprayed on 7-day intervals). 3. Aphids,
while neonics are generally good on aphids, OPs and pyrethroids are not as
reliable.
**Note: Pyrethroid resistance has
been documented in NW and SW Alabama in recent years. Pyrethroids should be
monitored closely for efficacy if used in all cotton growing regions of
Alabama.
Complications with adult plant bug management: Adults
can continue to move into fields over several weeks as weedy hosts slow play
out in wet springs. We suspect this could be the case this year. This may mean
we need to spray in consecutive weeks to keep populations below threshold. In
these situations, monitoring 1st position square retention on the
upper 2-3 nodes is critical. This is really the only way to determine the
efficacy of a spray for adults. Since a cotton plant puts on a new node every ≈3 days, we are evaluating new
growth the week following an application. As long as square retention is high
(>80%), our spray did its job regardless of adult plant bug numbers.
We have also received scattered reports of aphids across the
state. In most cases, populations were just high enough to be noticed, but in a
few there were enough to piggyback a shot with a trip for PGRs. Generally, we
do not see yield benefits to spraying aphids but it can happen. I suspect this
year they may have the potential to slow the crop down, particularly if we get
dry. Hopefully all the excess moisture we currently have will play in our favor
and help the aphid fungus develop a little quicker than normal.
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 to your local Extension Agent or myself (Scott Graham: 662-809-3368)
and 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 Podcast,
and the Syngenta Pest Patrol Hotline.
