Early-Season Beetle Activity in Cotton: Flea Beetles and Blapstinus Observations

I’ve consistently seen flea beetle damage on young cotton this season. Small feeding marks on the cotyledon leaves—especially in fields planted with untreated seed—are a sign of flea beetle activity. I’m mostly seeing pale-striped flea beetles. These insects have chewing mouthparts that scrape both the upper (more common) and lower surfaces of the leaves. At first, this doesn’t create visible holes, but as the damage ages, it turns into obvious holes in the cotyledons.

Flea beetle damage usually stays limited to cotyledon leaves and is mostly cosmetic. I haven’t seen much injury to seedlings in fields planted with neonicotinoid-treated seeds. Flea beetle infestations tend to be patchy and are more common along field borders, edges, and near drying weedy areas. Treatment is rarely needed and should only be considered if they begin to threaten stand establishment—which is very uncommon with flea beetles.

Striped flea beetle on cotyledon leaf

Another insect I’ve been spotting across several fields in the South Plains is the darkling beetle from the genus Blapstinus. These beetles are about ¼ inch long and black. Their larvae, known as false wireworms, feed on the underground parts of young seedlings. While only the larvae cause wireworm or false wireworm damage, the adult Blapstinus beetles are also known to feed on plants. You can often find several beetles clustered at the base of a single plant. Their chewing damage shows up on the stems, right at or just below the soil surface. If you see stand-threatening damage along with a heavy presence of these beetles, I recommend applying a foliar spray with a pyrethroid insecticide.

 

Early-Season Insect Activity in Seedling Cotton

The first insects I’ve seen feeding on seedling cotton this season are grasshoppers. I have spotted newly emerged grasshopper nymphs feeding on cotyledons and the first true leaves in localized areas of the South Plains. These young grasshoppers seem to be migrating in from nearby natural vegetation and weedy areas such as bar ditches.

If grasshopper numbers are high enough to threaten stand establishment, an insecticide treatment is recommended. Many areas—especially in the northern counties—will also need an over-the-top insecticide application for thrips. Products like acephate and dicrotophos (Bidrin) offer some control of grasshoppers, but their effects may not last long enough (especially if applied at the rates recommended for thrips) to prevent damage from new grasshoppers moving in. Therefore, it is important to keep a close eye on fields for continued grasshopper movement and be ready to make a second application if needed. Among all options, diamide insecticides offer the best grasshopper control, but they’re more expensive than pyrethroids or organophosphates. There are also products available with premixes of two or more insecticides, such as acephate + bifenthrin (e.g., Acenthrin), which provide control against both thrips and grasshoppers.

Besides grasshoppers, I’ve also seen chewing damage on cotyledon-stage cotton caused by Blapstinus darkling beetles and flea beetles in a few areas. This kind of insect feeding damage is more noticeable in fields planted without insecticide seed treatments. While minor cotyledon feeding usually isn’t a major concern, the damage becomes more serious when Blapstinus beetles chew on the stems—potentially knocking the seedlings loose.

Blapstinus beetles are the adult form of the false wireworm, a common pest across the South Plains. While there are no rescue treatments for the larvae (wireworms), adult beetle activity that threatens stand establishment may justify a pyrethroid spray.

Click here for the fact sheet on grasshoppers and their control