The upper gulf coast cooled down a bit this week, and some locations received some rain from our spotty storms. Most of our cotton is between 2-6 nodes above white flower (NAWF), but we did see a cracked boll this week. Some of the irrigated cotton around is holding out, but most reached cutout this week. 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. I've included heat unit charts below to help with spray decisions for our insect pests as our fields reach cutout. Temperature data for each county location is based on a field close to the center of each county. 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.
I've included two bolded lines at the cutoff for bollworms and plant bugs, and for stink bugs. Bolls that will reach maturity by harvest will be too hard for the respective pests to feed on at this stage.
Our bollworm egg has dropped off from last week, and we are seeing much less attempted damage from our worms, and a lot of the bolls are getting too hard for them to eat. The stink bug damage was lower this week, and a lot of our bolls are getting too big for stink bugs to damage as well. Below is my scouting information for the week of 7/1/2022.
The threshold for cotton aphids is 50 aphids per leaf, unless you have cracked bolls. Once we have cracked bolls the threshold for cotton aphids is 10 aphids per leaf. If you see aphid mummies in the field (tan or black dry and unmoving aphids), that's a good thing. Parasitoid wasps lay eggs in the aphids, and the aphid forms a mummy while the wasp larvae is pupating inside. These wasps, lady beetles, and lacewings can knock back aphid populations. Treatment for aphids is rarely justified, but I have seen some cotton at threshold this year. If you do decide to treat for aphids, do not use a pyrethroid. Pyrethroids and organophosphates are broad spectrum, and kill beneficial insects as well as your target insect, but pests like aphids bounce back much quicker than their predators do. Their high reproductive rate will allow their numbers to soar after a broad spectrum insecticide application kills all their predators.
|Aphid Mummies on Cotton|
|H. zea Larvae|
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. Below is a chart showing the overlap of Bt traits between crops and technologies.
|H. zea Eggs on Cotton|
|Evidence of Sucking Insect Damage on Cotton Boll|
|Sugarcane Aphids in Sorghum|
Photo: Kate Crumley
In sorghum we need to be scouting for sugarcane aphid before harvest. I've picked it up in sorghum in all three counties, but right now they populations I've seen have not been blowing up. The locations I've seen treated this year have not had rebounding populations. If it's blooming, we need to look for sorghum midge. Here are some links for just sugarcane aphid, and a more recently updated guide for sorghum insect management. Here are links to the threshold calculators for sorghum midge, rice stink bug, and sorghum headworm.
There is also a Women in Agriculture Ranch Tour and Workshop coming up on July 9 with our Prairie View Ag Agent, Braxton Mitchell. Please call the Wharton County Extension Office if you have any questions or check out this link to register.
Please check out our weekly IPM Audio Updates, the website to sign up to receive those is listed below. 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
Cotton Insect Management Guide
Development and Growth Monitoring of the Cotton Plant
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