We have gotten a lot of calls over the past couple of days on
grasshoppers across central and south Alabama. It can be tricky to tell how
many are adults or immatures, and most folks don’t carry sweep net in seedling
cotton to catch them, but at this point it is safe to assume that a decent
percentage of the population is adults. Unfortunately, we do not have good
thresholds for grasshoppers. It basically comes down to the level of risk a
farmer is willing to take. One thing we have noticed is that fields that
grasshoppers have reduced stands in in years past are likely to have it happen
again. In some conversations, the grower is willing to accept some risk, but in
most cases, they are not.
We are pretty limited with options for control of adult
grasshoppers. Acephate (0.67 lbs ai) has been the standard and most consistent option.
While some people have asked about pyrethroids, they are just too inconsistent on
adults. We have also been asked about Bidrin. While we have not tested it, it
would likely provide similar control as acephate as both are organophosphates.
The labeled rate for Bidrin on grasshoppers is 3.2 oz.
Thankfully, immature grasshoppers are not as difficult to control.
The acephate provides good knockdown control, but short residual. This is why
we recommend Dimilin (2 oz) be added to the tank. Dimilin provides good
residual control of immatures continuing to hatch in the field.
A few other points: Grasshoppers are not a “border pest.”
Eggs are deposited in tubes in soil in the fall and are distributed across the
field. Thus, the entire field should be treated, not just the borders. Cotton
is most susceptible in the crook stage as the emerging stem is just cracking
the soil surface. However, stand loss can be threatened after full emergence as
grasshoppers feed on the mainstems.
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.
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| Cotton seedlings damaged by grasshoppers |
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| Development of immature grasshoppers as they age |
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| Adult grasshoppers (note wings) |
