When it comes to managing thrips, there is one thing that cannot be argued: you have to do something at-plant. There are some rumblings of wanting to go with a base seed treatment (storage rate) to save some up-front costs and try to “spray our way out” of thrips. This is very difficult to do. Properly timing insecticide applications to manage thrips is hard with a seed treatment, it is nearly impossible without. The reason for this is largely due to the biology of thrips. Most thrips eggs are deposited in the cotyledons, so the immature thrips are hatching out just as the first true leaf is pushing out of the terminal. Thrips prefer to feed “inside” the emerging true leaves while still in the furl stage (pushing out of the terminal). Thrips are protected while inside the furl, so it is nearly impossible to get insecticide to them. This means that when the first true leaf finally expands, it has already been injured. This brings up a good point about expectations for thrips sprays. In most cases, the “next leaf” is the one being protected. In other words, if an application is made when the 2nd true leaf is in the terminal, that spray is most likely to protect the 3rd true leaf. We can’t really judge how well a foliar treatment protected that leaf worked for about 7 days (≈3 days per leaf to open). Generally, if no immatures are observed, then we can assume our treatment “worked,” however, the presence of adults does not mean the treatment did “not work.” Adult thrips may continue to migrate into the field after the residual of the treatment has worn off.
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| Varying levels of thrips injury to seedling cotton. |
With all that being said, what are our options for managing thrips?
1. Insecticide
Seed Treatments (ISTs) are the primary strategy used to manage thrips.
Performance of ISTs vary by year and location, primarily due to weather
conditions and thrips pressure. In low to moderate pressure, ISTs can “get the
job done.” Under high pressure, or if growing conditions are not conducive to
seedling growth, ISTs will likely require supplemental foliar treatments. Most
cotton seed companies offer multiple seed treatment packages, with the lowest
option (typically has the word base or basic), with a non-field active (or ‘storage’)
rate of imidacloprid. The second option (many different names) generally has a
full rate of imidacloprid, and option(s) 3 or 4 having additional nematicides
or biologicals. Thus, at least the 2nd option (e.g., Acceleron
Standard) is needed for thrips control.
2. In-Furrow
(IF) applications are another effective way to manage thrips. Based on our
past three years of research, we are no longer recommending acephate as an in-furrow
treatment for thrips. That leaves imidacloprid (liquid), which is the same
active ingredient as our seed treatments and the granular aldicarb (AgLogic),
which is still highly effective against thrips. If using in-furrow treatments,
then basic seed treatment options can be used, depending on the fungicide seed
treatment package needed. Supplemental foliar applications may still be needed,
particularly for in-furrow imidacloprid. Aldicarb treated cotton rarely requires
foliar applications for thrips.
3. ThryvOn
is the final option that can be used as an at-plant option for thrips. This is
a new Bt trait that will be commercially available in limited quantities in
2023. ThryvOn is also highly effective against thrips and is not expected to
need supplemental foliar treatments. Additionally, ThryvOn also has efficacy
against tarnished plant bugs, however less impacts than thrips. For more
information on ThryvOn cotton and how to best manage it in the Southeast, checkout
this Extension publication (ANR-2984).
If supplemental foliar insecticides are needed to manage
thrips, there are a few options to consider:
· Acephate (3 oz/A) is an effective and relatively
inexpensive option, however it has the potential to flare secondary pests such
as spider mites and is the least rainfast of the available recommended options.
· Bidrin (3.2 oz/A) is another option that is
effective and less likely to flare spider mites and is more rainfast than
acephate, however it is more likely to cause crop injury when tank-mixed with
herbicides.
· Dimethoate (6.4 oz/A) is another cost effective
and efficacious product with good rainfastness, however it is the most likely
to cause crop injury when tank-mixed with herbicides.
· Intrepid Edge (3 oz/A) is another effective
option. Intrepid Edge is less likely to flare secondary pests but may need the
addition of a surfactant to help with efficacy.
· Pyrethroids are not effective and
should not be used to manage thrips.
In summary, effective thrips management is important to get
the crop off to a fast, vigorous start. The best way to manage thrips is to use
a recommended insecticide at-plant insecticide (IST or in-furrow) or
ThryvOn cotton. Foliar insecticides are meant to supplement at-plant
treatments, not replace them. We will be updating the blog soon with the results
from the Thrips Infestation Predictor Model for Cotton. 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.