Defoliation Guides

Open Cotton
Kate Crumley

Howdy,

Our season is rapidly wrapping up, most of the grain is out of the field, and I've seen some soybeans harvested this week as well.

Most of our cotton is opening up, and even our latest fields should be opening next week. We are a good ways past cutout, and past susceptibility to any insect damage in almost all locations. There are very few fields still susceptible to stink bug damage. I've seen a couple fields defoliated this week, and next week I expect to see a good deal more ready for defoliation.

Defoliation is usually recommended at over 60% open bolls, or 4 nodes above cracked boll. For more information, here are links to a defoliation guide from the Texas Row Crop Newsletter, the 2019 Mid South Defoliation Guide, and the Wharton county defoliation test results from 2017.

Cutout occurs when carbohydrate supply equals demand, and vegetative growth ceases. When the plant reaches cutout, no more harvestable fruit is set. This is normally at 4 to 5 NAWF. Cotton is no longer susceptible to economic damage by plant bugs and bollworms at 350 degree days (DD60), or heat units, past cutout, and is no longer susceptible to economic damage from stink bugs at 450 DD60 past cutout. Bolls that will reach maturity by harvest will be too hard for the respective pests to feed on at this stage.

The fields I check are no longer at risk for damage from bollworms and stink bugs. If we are finding any plant bugs, they're mostly brown and green stink bugs, some leaf-footed bugs, lygus bugs, and tarnished plant bugs. These are all below threshold, or like most of our fields, in places that are no longer susceptible to damage.

Evidence of Sucking Insect Damage on Cotton Boll
Kate Crumley

When scouting for stink bugs, check the inside of the bolls for warts, lesions, and stained lint. Above is a photo of a boll with potential stink bug feeding damage from the outside, note the slightly raised look of the dark spots. Be sure to open the bolls to confirm it is damaged, other sucking plant bugs may be unable to get through the carpal walls, and the inside will be clean. The economic threshold can be found below, depending on how long the field has been blooming. It is based on the percent damaged bolls with live bugs present. This year we've mostly seen brown stink bugs in cotton so far, and some of the brown stink bug populations in our area have been shown to have some resistance to pyrethroids. We can stop scouting for plant bugs at 350 DD60 past cutout, and stink bugs at 450 DD60.

Green Stink Bug adult
Photo: Kate Crumley

Carpal Wall Warts from Stink Bug Feeding Damage
Photo: Kate Crumley

If you've got soybeans, we need to be scouting for stink bugs right now. The red banded stink bug thresholds are now 4 bugs per 25 sweeps for R2-R6, and 10 bugs per 25 sweeps for R6.5-R7, unless we have rainy and humid conditions, then we should continue checking through R8. The threshold for red-shouldered, brown, green, and southern green stink bugs is 9 bugs per 25 sweeps for R2-R6, and 20-25 sweeps after R6, and we can stop checking at R6.5. Since color can vary on stink bugs, the best way to check if you are unsure if you are finding red banded stink bugs is by looking at the underneath of the insect. A red banded stink bug has a large spine just below the legs, green stink bug has a short one, and the other species do not have a spine at all. I've seen mostly brown stink bugs, but some of the consultants I've spoken to have picked up greens and red banded stink bugs as well. The red banded stink bugs hit several of our fields late last summer, and we need to stay vigilant checking for those in our soybeans until R8.

Red Banded Stink Bug, showing ventral spine
David Kerns

Green Stink Bug, showing short spine
David Kerns

Check out our weekly IPM Audio Updates, the link is below. As always, if you have any questions feel free to contact me either by email or calling the office. Have a good weekend everyone!

Check out our weekly IPM Audio Updates

2017 Wharton County Defoliation Test

Texas Row Crops Newsletter: East and South Texas Cotton Harvest Aids

2019 Mid-South Cotton Defoliation Guide

Cotton Insect Management Guide

Development and Growth Monitoring of the Cotton Plant

Fall Armyworms in Pasture

Bermudagrass Stem Maggot