Texas Blacklands Cotton: Grasshoppers, Aphids, Spider Mites Taking Advantage of Hot, Dry Conditions

    Spider mite injury in cotton. Photo: Louisiana State University

    The condition of the cotton crop is continuing to deteriorate as we keep stringing days with triple digit highs together and little to no moisture across the region. There were some pop-up showers received over the last week that brought as much as 0.5 inches of rain, but these amounts were too little too late for the crops in the field and did nothing but halt corn harvest operations.

    It is getting hard to find things to talk about in these newsletters and out weekly audio updates as the hot and dry conditions continue to negatively impact both the crops and pest activity across the region. However, there are still some insect pests active in area cotton fields including spider mites, aphids, and grasshoppers.

    Currently, none of these pests have been found at their respective economic threshold but should continue to be watched to avoid more yield loss. Also, this week I started to notice some of our earliest planted cotton starting to open fully mature bolls, and some fields having bolls open prematurely which can have a negative impact on the fiber quality of the lint produced within that boll.

    Grasshoppers continued to be found infesting cotton fields. Some of these fields have had grasshoppers for a few weeks now, and some are just starting to have them move into the field. Grasshopper can do a good amount of damage to area cotton, by defoliating the crop and even severing the terminal from the plant.

    At this point in the growing season with our environmental conditions the biggest issue with grasshoppers is defoliation, as removing the terminals at this point will have little to no effect on the ability of the plant to mature the bolls that will make it to harvest. Excessive defoliation of the crop, however, will reduce the plant’s ability to create enough sugars that will be needed to mature what bolls it has set on the plant.

    This could then lead to fiber quality issues if the plant is not able to fully mature the seed and fiber within the bolls. Treatment for grasshoppers is recommended when they have defoliated approximately 30% of the canopy, and risk defoliating more.

    There are several products that will effectively manage grasshoppers, but some should be used with caution as they could flare aphids and/or spider mites. Given the current environmental conditions I would recommend either a 0.9 fl. oz shot of Vantacor which will provide about 10 days of residual activity and not flare aphids or spider mites, and another option is 8 fl. Oz. of Bidrin which will not have the residual activity like Vantacor but will not flare the aphid and/or spider mites populations like the labeled pyrethroids would.

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    Spider mites remain present in the fields they were found in last week, but thankfully, since they were found in the fields two rain events have been received on them which slowed the population development of the spider mites.

    However, as we continue to have record breaking temperatures in the forecast, spider mites could easily explode in area fields and start defoliating the crop before the plants have had a chance to fully mature the bolls set on the plant.

    Continue to scout for spider mites, and if you see 40% or more of plants with visible feeding damage and a healthy spider mite population, it is recommended to treat the field to avoid premature defoliation of the crop. Learn more about the bold jumping spider and other spiders here!

    There are several miticide products available for spider mite management in cotton, but probably the cheapest option that will give you the most return on investment will be products containing the active ingredient abamectin like Agri-Mek SC, Abba Ultra, and other generics.

    Aphids can still be found in area cotton fields, but for some reason they have not exploded into populations that would justify treatment like they have in the Brazos River bottoms. This is likely because the excessive heat and ongoing drought has led to the crop to start wilting and the crop is not healthy enough to support an aphid population.

    However, as we are nearing the start of bolls opening across the region, we need to keep a close eye on the aphid populations to avoid some issues aphids can cause in cotton.

    When aphids are present in cotton when bolls start to crack open and expose the lint, the honeydew these aphids produce can land on the lint and cause sticky cotton which can create a nightmare for harvest and ginning operations, and even lead to a decrease in the loan value of cotton bales where sticky cotton is present.

    The current economic threshold for aphids in cotton is about 60 aphids per leaf, but as soon as we start seeing cotton bolls open that threshold will drop down to only 10 aphids per leaf. Sadly, aphid treatment is not a cheap application as pyrethroids are not effective against cotton aphids, and the recommended products include Sivanto, Transform, and Sefina.

    Treatment could be avoided if there is a chance for rain that could wash the honeydew from the lint, but the way this season has progressed and looking at some long-term forecast, I would not bank on receiving rain before we start harvesting.

    If you run into a situation where aphid numbers are reaching the economic threshold and you have questions about what to do or spray, do not hesitate to contact me and we can go over some potential options as treatment decisions will likely be based on a field-by-field basis.

    The oddest thing observed in cotton this week is finding some bolls that are opening prematurely. This is not an uncommon condition for cotton as it has been seen in other parts of the cotton belt, but it has not occurred here very often. Talking with Ben McKnight the State Cotton Specialist, this is caused when soil conditions get extremely dry during the later stages of the bolls maturing, and the plant is aborting the seeds within the boll.

    This will lead to potential fiber quality issues as the fiber produced in these bolls will not fully mature and have a low micronaire and short staple.

    Talking to others that regularly check cotton, this is being found across the Blacklands, as well as in the Brazos River bottom and Upper Gulf Coast. Premature boll opening can be identified two ways, first when bolls below it are not yet opened, and second when inspecting the seeds within the boll, they are not fully developed, and the seed coat has not begun to darken.

    This is without a doubt a problem brought on by the ongoing drought and prolonged period of excessive heat. I received some pictures from Mark Nemec this week from where he was taking temperature readings of the plant canopy and the soil surface. On Tuesday afternoon, one of his soil temperature readings reached 169 degrees. This is leading to a high rate of evaporation from the soil and makes it hard for roots to uptake water.

    When plants are not able to absorb water it is not able to properly conduct transpiration which is much like when you and I sweat, and when this is not able to occur it is hard for the plant to regulate canopy temperature.

    In fields with adequate soil moisture, when ambient temperatures rise to over 100 degrees, canopy temperatures can easily be 20–30-degree cooler, but when plants are unable to transpire properly the plant canopy temperature can easily reach the same temperature as what is read by a thermometer, and another phot Mark sent me show this accurately where the surface of cotton bolls in the upper canopy reached temperatures as high as 122 degrees.

    Thankfully, this premature boll opening is not occurring at a high frequency within fields and may not have a major impact on the fiber quality grades on these fields.

    Some of the earliest planted cotton in the areas is starting to have mature bolls opening, and defoliation operations in the area will likely start around the first of August. Given the small canopy most fields have this year defoliating the crop should not be difficult.

    Harvest aid application selections this year will likely depend on the yield potential for the crop, and I highly recommend conducting boll counts over the next few weeks to determine the fields’ yield potential. I would like to issue a little caution when conducting boll counts this year, as bolls this year are smaller than normal, and it will take more bolls to make a bale than usual.

    In a normal year we use a boll count number of about 10 bolls per row foot on 30-inch cotton to produce 1 bale (12 per row foot for 38” cotton), however, with the size of these bolls it will probably take at least 15 bolls per row foot to make a single bale of cotton.

    I suspect that our typically 2 fl oz of Ginstar and 2 fl oz of Dropp will still preform good as a defoliation shot but kill shots this year will probably be decided based on a few different factors. Factors that may affect the choice of what to kill cotton with prior to harvest include 1) how well the plant was defoliated, 2) weather forecast, 3) expected yield, and 4) how quickly you want/need to get into the field to strip.

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