Stink Bugs and Rain

Howdy,

I am currently looking for high numbers of rice stink bug in sorghum (even in fields past where they can cause damage), as well as populations of sugarcane aphids to collect. If you've got a field with either of those, please give me a call or send me an email. I've also been recording and editing weekly audio updates with Dr. David Kerns, Tyler Mays, and Dr. David Drake. Our other IPM agents and specialists are recording as well, so if you'd like to hear what's going on with us or with my coworkers across the state, check those out. If you sign up, you'll receive a text message when the update posts with a link to the recording. You can sign up or listen at this website.

Cotton Field in Matagorda County
Kate Crumley

This week most of our cotton is between 4-8 nodes above white flower (NAWF), and our later replanted cotton is starting to bloom. We are checking for stink bugs and bollworms in almost all of our cotton, but our scouting has been limited this week due to the near constant rainfall.

Almost everything should be out of concern for fleahoppers by now, even the later replanted cotton. We are currently looking for bollworms and stink bugs in cotton. Our bollworm egg lay has stayed fairly low, but it everywhere. Everything we've looked at has at least a light number of eggs, the highest egg lay we've seen this week was 6%, and that field had one small live bollworm. We especially need to be scouting our second generation cotton, Twinlink, Bollgard 2, or Widestrike cotton, for live worms, damage, and eggs. The stink bug pressure has been picking up slightly, and I have heard reports from consultants that a few places have required treatment. The highest we saw this week was only 2% damage with no live bugs. We've mostly seen brown stink bugs if we've seen them at all. This week's scouting results are below. We did get rained out a good bit this week.

Helicoverpa zea is our cotton bollworm and corn earworm. These 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 the corn matures, the next generation of bollworm eggs will be laid in cotton. I start looking for bollworm eggs in cotton when that field starts blooming. We are finding some small larvae now, but our survivorship in cotton has been low compared to previous years.

Small H. zea Larva on a Cotton Boll
Kate Crumley

Large H. zea Larva
Kate Crumley

Our scouting guide recommends checking in the top 1/3 of the plant, but it's important to also pull bolls and flowers from lower to check as well. Egg lay has been occurring low in the plant as well, and it's not uncommon to find small larvae or eggs in flowers and bloom tags. We also have seen small larvae feeding and entering bolls either on the very tip of the boll, or along the seams of the bolls. This makes the entry wounds more difficult to find, but the damage is easy to see if you pop open the bolls.

Our Bt traits overlap across corn and cotton. If the caterpillars survive the traits on corn then as adults fly to cotton to lay eggs, it's likely their offspring will survive the same traits on cotton. The chart above shows the overlap of Bt traits between crops and technologies.

H. zea Eggs on Cotton
Kate Crumley

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 plants, checking the entire plant, including blooms and under bloom tags, for caterpillars and eggs. I also pull 25 half grown or larger green squares to bolls and look for bollworm damage. 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). Bolls with slight dark indentations like the photo below could be chewing damage from bollworms. Look closely at dark spots to see what they're from. Early superficial damage like the photo below is unlikely to cause fruit drop, but if the caterpillars survive or get through the carpal walls, it can quickly become a problem.

Chewing Damage on Cotton Boll
Kate Crumley

Evidence of Sucking Insect Damage on Cotton Boll
Kate Crumley

We've picked up a few stink bugs, and a few consultants have recommended treatment for them in their fields. 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.

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 a couple of our other species as well so far.

Red Banded Stink Bug, showing ventral spine
David Kerns

Green Stink Bug, showing short spine
David Kerns

Most of our sorghum is wrapping up, a few places have even been harvested. We do have a good bit of it sprouting, unfortunately. Our sugarcane aphid numbers have been relatively low, but I am seeing numbers increase, especially along field margins. It's a good idea to check for them before making a burn down application. For more information on scouting sorghum and insect pests, check out this publication. If you need economic calculators for sorghum pests, those can be found here for midge, headworm, and rice stinkbug. Please call me if you have rice stink bugs heavy in a field, we are doing pyrethroid bioassays and I need 3 more locations.

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

PGR Management Considerations

Plant Growth Regulators as Tools for Challenges

Cotton Insect Management Guide

Development and Growth Monitoring of the Cotton Plant