Plant Bugs and Bollworms

H. zea moth
Kate Harrell

Howdy,

  This week we're still monitoring for cotton fleahoppers feeding on squares, and their numbers have increased this week. In older cotton with blooms I am looking for bollworms, as well as plant bugs and stink bugs. I've seen bollworm moths flying a bit this week, and my field scout found a couple small larvae in a field near the Wharton county fairgrounds. I have also seen some square drop due to stress lately. Some of the places water stood for a couple of days may be showing some fruit loss now.

  I did get a question on verde plant bugs this week, and saw one this week. The threshold for verde plant bugs is 20-25 insects per 100 plants with using a beat bucket. Verdes can feed on fruit up to bolls about an inch in diameter.

Nymph (A) and adult (B) of Verde plant bug, Creontiades signatus Distant (Hemiptera: Miridae), which causes lint and seed staining and deterioration, seen in green (C) and open (D) cotton bolls. https://ccag.tamu.edu/entomology/

  Fleahoppers feeds on plant materials, and will feed on cotton squares. Keep a sharp eye out for this insect, the adults are very flighty and are often easily scattered when walking fields. I try not to let my shadow hit a plant before I get close enough to look at it so I can see the adults before they fly. Below I have two photos, one of the nymph and one of the adult insect. The nymphs of these insects are also quite small, about the size of an aphid. They are also a pale green color, but lack wings. They lack cornicles (tailpipes) that an aphid would have, and tend to be more mobile than an aphid. Fleahopper nymphs also lack the bands on the antennae a few other species of plant bugs have, and have a similar body shape to the adult bug.

Cotton Fleahopper Nymph
Kate Harrell

Cotton Fleahopper Adult
Kate Harrell

  Fleahopper feeding will cause squares to drop. Plants can recover for and compensate for some square loss, but the threshold for fleahoppers is 15-25 per 100 plants. I check for fleahoppers by inspecting the plant terminals once they start squaring. I look at 25 plants per stop in the field, usually checking 100 plants total in an 80-100 acre field, more if the field is larger.

  The chart above with action thresholds if from the cotton insect guide, and the one below containing insecticide suggestions is from cottonbugs.tamu.edu.

  Lygus bugs will feed on cotton squares, flowers, and small bolls. Feeding can cause damage to blooms (dirty blooms and damaged anthers, or puckered petals), deformed bolls, stunted growth, fruit shed, and small lesions on bolls.

Lygus Bug nymph
Kate Harrell

Lygus Bug adult
Kate Harrell

Chart from Cotton Insect Guide

  Stink bugs have been showing up as well. To scout for stink bugs pull 10 to 20 bolls about an inch in diameter from four places in the field. Check the inside of the bolls for warts, lesions, and stained lint. The economic threshold for stink bugs is 20% or more of the bolls with internal damage and stink bugs present. Some of the brown stink bug populations in our area have also been shown to have some resistance to pyrethroids. 

Green Stink Bug adult
Kate Harrell

Carpal Wall Warts from Stink Bug feeding damage
Kate Harrell

  Bollworms, Helicoverpa zea, are caterpillars that feed on multiple crops and vegetables. In cotton they feed on squares and bolls, causing fruit loss. The last few years we had high numbers of this insect in our Bt cotton as well.

H. zea caterpillar in cotton square
Kate Harrell

  To scout for cotton bollworms I use the terminal and square inspection method. I make about four stops in a field, more if the field is larger than 100 acres. At each stop, I look at 25 plant terminals, checking the upper third of the plant for caterpillars and eggs. I also pull 25 half grown or larger green squares to bolls and look for bollworm damage. This week there were a few moths flying around in a couple of the fields in Matagorda county, and in one near Palacios we found two eggs laid. When documenting egg lay, if I find more than one on a leaf, I only count it as one. This caterpillar is highly cannibalistic, and generally only one caterpillar will result from eggs too near each other. The economic threshold for bollworms is 6% damaged bolls with live caterpillars present. In areas like ours on the upper gulf coast with documented Bt failures, the threshold for eggs on single and dual gene cotton is 20% (20 plants out of 100 with at least one egg). If you're finding bollworms in cotton or in corn, especially in viptera fields, please give me a call.

Cotton Insect Guide

 The current A&M recommendation is to use pyrethroids with caution. In areas needing residual control Prevathon at 18-20 fl oz or Besiege at 9-10 fl oz works well. If you don't need residual control you can get by with Prevathon at 14 fl oz or Besiege at 7-8 fl oz.

Cotton Insect Guide

  

Heat Unit Accumulation for Wharton, TX

  Corn this week has had southern rust picking up in places. This disease can spread rapidly, and places you see it should be monitored daily. Check out Tom Isakeit's publication on this fungus.

  I hope you all have a good weekend. If you're not sure what kind of insect or issue you have, feel free to drop by the Wharton county office or give us a call.

Sincerely,

Kate Harrell

Looking for more information? Check out the Cotton Insect Guide

Need help with weed control? Check out the Weed Management Guide

Need info on Southern Rust? Check out this Southern Rust of Corn publication

Information on cotton bollworm resistance problems