Texas Blacklands Cotton: Hot and Dry, Bollworm Activity on the Rise

    Bollworm, cotton square. Photo: Aaron Cato, University of Arkansas


    Another week of extreme temperatures and no rain, and at this point it is hard for event the biggest optimist in the area no to feel pessimistic about the area crops. Corn harvest operations have started in the South and Western portions of Hill County this week, and I have not heard any yield reports yet.

    Cotton fruit shed is continuing at a high rate, and any new squares are quickly falling off the plant, and even young bolls are being shed from the plant shortly after flower closes. What bolls were set on the plants about 2 weeks ago, is what we will have to contribute to cotton yields unless we get some much-needed rain in the area soon.

    Cotton root rot symptoms are showing up in a few fields, and now is the time to start taking note of where these locations are in you farming operation and within the field. Cotton pest activity is low, but there are some pest activity that warrants scouting operations to continue.

    This week I started picking up on bollworm damage in two gene Bt trait packages, spider mite moving into field margins, and aphids starting to move to new fields. Stink bugs and grasshopper remain active in some area fields, but populations and damage have not increased much over the last week. Here to a safe corn harvest and more favorable weather soon


    While I am typically an optimistic person about a cotton crop, the lack of measurable rain fall and over 10 days of 100+ degree days already this year it is hard to stay optimistic about this crop. Normally, cotton can withstand periods of triple digit temperatures, but when you pair them with depleted soil moisture profiles the plants are not able to combat the adverse weather conditions.

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    This is leading to fruit including squares and small boll from being shed from the crop, and the bolls that somehow luck out and stay on the plant are malformed and/or smaller than normal.

    The warm temperatures depleting the soil moisture profile is bringing a slough of nutrient deficiency symptoms in area cotton fields, and probably the most prominent of them in the area is Potassium. Potassium deficiency symptoms start as interveinal chlorosis and as the deficiency continues unfixed the leaves will develop a yellowish bronze discoloration.

    Potassium deficiency is a major issue in cotton as it can lead to issues like fruit loss, defoliation, and it weakens the plants defense system against some foliar diseases. Last year we conducted a foliar Potassium application trial and saw no benefit from making these applications, however, a few days after application the field did receive some rain that may have allow the soil potassium to get back into solution and be absorbed by the plant roots.

    The best way to correct this deficiency is to fix the cause of the problem which right now is the lack of soil moisture.

    Cotton bollworm activity increased over the last week, with eggs still being found this week along with moths still floating around area fields. Currently, it appears that the amount of moths active in fields is very localized with one field having high moth activity and then right down the road moth activity being very light.

    I did start finding some bollworm damage to small bolls but I did not find any live worms. This bollworm damage is currently being found in some Bollgard 2 varieties in the area, and it is no surprise to me to see the damage in the fields because of the level of bollworm resistance to the Bt toxin observed over the last couple of years.

    On top of that our plants are not health and actively growing which is likely cause the concentrations of these Bt toxins to be reduced in the plant tissue. Thankfully, I am seeing a good amount of minute pirate bugs in cotton fields that can help control small bollworms. While scouting this week I did observe that moth laying eggs deeper in the canopy than normal, and are starting to lay eggs on the branches, lower leaves (both upper and under side), bracts, and even white flowers.

    Continue to monitor fields for bollworm damage, especially those that only have two Bt toxins (Bollgard 2 and TwinLink) as these fields are at the greatest risk for significant damage with some fields already treated in other parts of Central Texas. If we do get into a situation where we think an application may be need, the economic threshold for bollworms is 6% fruit damage with live worms present in the field.

    Insecticide applications for bollworms should be made as soon as possible since once they get over ½” and start moving deep into the canopy product efficacy can drop off. Recommended products for bollworms are those containing the active ingredient chlorantraniliprole (Prevathon) and these products include Vantacor (former Prevathon), Besiege, and Elevest.

    If you are in the situation where you need to treat for stink bugs and bollworms at the same time, Elevest would be a good product for this application as it is a premix of Vantacor/Prevathon and bifenthrin.

    Thankfully, stink bug number and damage has not increased much since last week when a few fields on the western side of Hill County needed treatment.

    After anticipating spider mites in area cotton fields for the last month, I finally found two fields north of Hillsboro where spider mites were starting to move into field margins. The excessive heat and lack of rain in the 10-day forecast is looking like these spider mite number could soon reach economic levels and justify treatment.

    The fields where these spider mites were found were along a gravel road that was being frequented by biosolid truck and the wind was blowing the caliche dust into the field margins. For some reason it seems spider mites populations commonly start in or around areas where this caliche dust accumulates on the plant, and it is likely due to reduce beneficial activity in these areas.

    Spider mites populations can get out of hand quickly, and if not managed in a timely manner can lead to premature defoliation of the crop. The economic threshold for spider mites in cotton is 40% of plants with visual signs of feeding with an actively growing spider mite population.

    Common miticide products include those containing abamectin (Abba Ultra and Agri-Mek SC), Oberon, Portal and Zeal. The later three of these products are harsher on the beneficial insect and can lead to a resurgence of the spider mites, or even aphids reaching economic levels. If you are treating for bollworms or stinkbugs product selection will have a major impact on if or when you may need to treat for spider mites.

    Aphids remain a common occurrence in cotton around the area, and over the last week I started finding them in new fields and moving to more plants in some fields. In fields where aphids are present, they currently are not uniform across the field and currently just a couple of plants heavily infested spread randomly across the field.

    I have not found a field yet that would justify treatment for aphids yet, and thankfully these pockets of aphids do have some green lacewings and lady beetles helping keep the aphid population from expanding. Currently, the aphid threshold in cotton is around 50 aphids per leaf, but will likely start shifting to 10 aphids per leaf in about 2-3 weeks when we start seeing some cotton bolls open around the area.

    The reason for the aphid threshold to drop so low once cotton bolls start to open is to avoid sticky cotton issues. If you are seeing a decent aphid population in area cotton fields I would like to conduct an efficacy trial on them, as this is a pest we can see yearly but populations in a normal year usually do not build to levels that are suitable for an efficacy trial.


    The sorghum I was looking at over the last few weeks was cut over the last 7-10 days for hay, and I no longer have a sorghum field(s) to look at to monitor sorghum aphids (formerly sugarcane aphid). I have received reports of the aphid being present in areas south of Hill and Northern McLennan Counties, and in some of these fields their number have exploded over the last 7-10 days, to levels that justify treatment.

    As our sorghum acres near harvest the potential for yield loss decreases, but the potential for harvest issues increases, as their honeydew can gum up the combine and slow down harvest efficiency.

    Continue to monitor area sorghum fields for sorghum aphid populations, and if you have question about treating or what to spray please contact me, as the recommendation will depend on the length of time to harvest and if a desiccant is going to be applied to prepare fields for harvest.

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