Texas Blacklands Cotton: Some Stink Bug Damage, Low Numbers of Bollworms, Aphids

    Unopened cotton boll damaged from stink bug feeding.

    GENERAL:

    Cotton in the area is still blooming and setting fruit, but some area cotton fields are quickly approaching cutout. Aphids have returned to some area fields, but currently populations are remaining well below the current economic threshold. Stink bugs are also present in area cotton fields and causing damage, with some fields requiring treatment.

    Currently, our bollworm numbers are low, and there is minimal damage in out Bollgard 2 and TwinkLink cotton trait packages. As our cotton continues to bloom and set more fruit the demand for water and nutrients is high, and the drying soil moisture is starting to limit the amount of nutrients absorbed by the plant, and this has led to some physiological fruit shed.

    Sorghum acres are starting to be treated with a kill shot for harvest preparation, and in these fields and those not yet sprayed we need to keep an eye out for sugarcane aphids as they are present in some area sorghum fields.

    Thanks to the recent dry spell, a lot of corn acres have dried down to 15% moisture and harvest operations have started.

    COTTON:

    Our bollworm pressure over the last 3 to 4 weeks have been low, and all the Bt trait packages have held up against our current bollworm pressure. I have a variety trial outside of Abbott that includes and non-Bt, TwinLink, TwinLink Plus, Bollgard 2, Bollgard 3, and Widestrike 3 varieties, and for the last four weeks I have been checking 100 bolls and 100 squares for worm damage once a week.

    During the first four weeks of this project I have only found minimal damage in the TwinLink and Bollgard 2 varieties. Damage in the non-Bt has been lower than what would be expected with 9% damage the week of July 23rd and 13% damage the week of July 30th. Last weekend we had a full moon, and I had suspected to see a decent moth flight this week, but the trap numbers have indicated that the moth flight was lighter than expected.

    As our season moves along we need to be vigilant of bollworms in our Bollgard 2 and TwinLink varieties until the crop has accumulated 350 heat units past cutout. The economic threshold for bollworms in cotton is 6% damage fruit with worms present.

    Recommended insecticides include Prevathon at 14-21 fl. oz./acre, Vantacor (reformulation of Prevathon) at 1.2-1.9 fl oz/acre, and Besiege between 6.5 and 12.5 fl oz/acre, using the higher rate ranges for larger worm and/or longer residual activity. The downside of using Besiege is that it also include lambda-cyhalothrin which will kill the beneficial insect population and potentially flare aphid and spider mite populations.

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    Stinkbugs are present in some area cotton fields, and some fields have reached the economic threshold. Most of the fields I have found at the economic threshold are in Western and Northern Hill County. Fields around Abbott east to Malone and south to Waco are currently running damage levels well below the economic threshold.

    Most of the stinkbug I am finding in area cotton fields are brown stinkbugs, but there are occasionally some green stinkbugs showing up in the cotton as well. Stinkbugs damage cotton by piercing small and medium sized cotton bolls to feed on the developing seeds.

    This feeding damage stains the lint as the oils from the developing seeds ooze out into the developing fibers, and also opens the bolls up for potential infection by the various bollworm pathogens. Stinkbug damage can also lead to hard lock issues, where when the boll opens the lint does not fluff out like it typically does. Signs of a boll being fed on by a stink bug includes wart like growths on the carpel wall, and/or stained lint.

    To scout for stink bugs the most reliable way is to collect 100 bolls from four different regions of the field, and opening bolls to check for internal feeding damage. The economic threshold for stinkbugs in cotton depends on the week of bloom, and for most of the areas cotton the current economic threshold is between 10 and 20 percent damaged bolls.

    There are a number of insecticides labeled for stinkbug management in cotton, but most pyrethroids are not very effective at controlling brown stinkbug. Recommended insecticides for stinkbug management include bifenthrin at 6 fl oz/acre and Bidrin at 8 fl. oz./acre, and Acephate at 1lb of active ingredient per acre (various rates depending formulation).

    If a field needs to be sprayed for stinkbugs and have aphids present, including a couple of ounces of imidacloprid can provide some suppression of the current aphid population, but complete control of the aphid population should not be expected.

    Aphids are being found in some fields in the area, but their populations are currently well below the economic threshold, but if we are having to treat fields for stinkbugs we need to keep a very close eye on their numbers as they can increase rapidly. Aphids can be found feeding on just about any part of the cotton plant, and feed by sucking the sap the plant would otherwise use to fill out the fruit and/or grow.

    Excessive aphid feeding can cause the leaves to cup downward, and could potentially cause some squares to be shed from the plant. Thankfully right now we do not have any open cotton boll, and unless the aphids populations explode will not be a major issue.

    Our current economic threshold is 40-70 aphids per leaf, but once bolls start to open that threshold drops to 10 aphids per leaf. Aphids can be managed with various insecticides, but there have been reduced efficacy with some neonicotinoids like imidacloprid and Centric.

    The best available insecticides for aphids include, Transform, Intruder, and Sefina.

    SORGUM:

    Most sorghum acres are past the point where yield loss from any pest will happen, but we need to continue watching sugarcane aphid populations. Currently sugarcane aphid populations are low, and over the last week or so there has been a reduction in sugarcane aphid numbers thanks to increased beneficial activity.

    As our weather stays hot and dry, we need to keep an eye on their numbers so we can treat fields before they produce a lot of honey dew on the leave and in the head that can cause harvest issues. If you do need to treat sorghum for sugarcane aphids to avoid harvest issues the best insecticides include Transform, Sivanto and Sefina, all of which carry a 14-day pre harvest interval for grain harvest.




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