Texas Upper Coast Pests: Watch for Bollworms, Get Ready for Plant Growth Regulators

This week we’ve been finding some stink bugs and some bollworms in cotton in all three counties. Currently we are mostly finding damage and newly hatched larvae. As the grain continues to dry down, expect to see more moths moving around.

Bollworm eggs are small, round, generally singly laid, and have ridges meeting at the top of the egg. These insects are highly cannibalistic, and will eat each other if more than one larvae is on a leaf. The photo below has two eggs, but I would count this as one egg while scouting, since only one of those would live long enough to feed on the plant.

The eggs can be found anywhere on the plant, generally on the tops of leaves. This week we have found more eggs in the mid canopy. Sometimes eggs are even laid on flowers and bloom tags.

We’re still finding stink bugs in cotton as well. This week we found a few nymphs in Jackson and Matagorda counties.

Bollworm Eggs Photo: Kate Harrell

Some of the cotton around has begun to get a little long in the internodes since the rain we got a couple weeks ago. The best time to use a plant growth regulator (PGR), mepiquat chloride (MC), is dependent on plant height and internode length. Plant height should be 30 to 35 inches in 30 inch rows, and in 40 inch rows should be no more than 40 to 45 inches.

Optimum plant height should be predicted using row width multiplied by 1.1. MC suppresses stem elongation in newly formed internodes by up to 50% of normal growth. The minimum MC concentration in the plant necessary to provide a maximum level of reduction is 12- 15 ppm per acre, but internodes will not grow shorter than 50% of the normal length with higher rates.

Before the plant has reached 15 to 20 days past first bloom, measure the top 5 internodes. If the internodes are 1.4″ or less, no MC should be applied. If the internodes are between 1.4″ and 1.6″, treatment is optional.

Treatment is optional in internodes measuring between 1.6″ and 1.8″, but if it has rained recently or you are planning to irrigate, treatment is recommended. If the internodes are longer than 1.8″, MC should be applied. Check out this article for more information on PGRs.

Headworms and stinkbugs are in sorghum right now. The best way to scout for damage from these insects is to use a bucket. Rattle a grain head around in a bucket to see what falls off of it. Adult stink bugs will fly, often very quickly after being knocked from the plant, so be aware of anything taking off when you go to look in the bucket.

Folks in all three counties have been treating for stink bugs lately, but the earlier planted sorghum is hardening enough to be past the point of concern. Check out the rice stink bug calculator and the sorghum headworm calculator to check economic threshold levels.

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