Texas Plains Pest Management: Lots Happening in Fields, Get Out and Scout

    Photo: Texas AgriLife Extension

    General Status

    Even with a timely, if not variable, rain this week, you would think we could take a sigh and relax for a bit. Traditionally this is the most important cotton scouting week on the Texas High Plains.

    This was established by the bollworm (corn earworm / sorghum headworm) as they moved from maturing corn and migrated in from the south, but generally speaking, if a field has made it this far in at least fair to good shape in our extreme environment, the pests that have been building all summer long converge on all those sweet bolls, or other types of crops finishing out their production for the year.

    A lot of things have changed in our local recent crop production history. Irrigated acres have decreased while the corn planting window has widened, no-till fields allow more soil overwintering pests to survive locally, more pest species have moved in, Bt technologies altered control techniques while lessening reliance on insecticides and arguably changed some pest behaviors.

    With far too many changes to accurately reference, one thing has not changed. The importance of scouting and making management decisions this week for the region. This year is certainly no exception.

    There are a lot of things happening in our fields right now, and if action needs to be taken, it is likely on a field-by-field basis. It has been high all year long, but the need to be in our West Texas Fields gathering data has not been higher than it is right now.

    Cotton

    With the rains from earlier this week, and the fact that all of our field scouts and interns are setting in a classroom today (I still view starting classes before Labor Day a criminal act), and several active research trials, we have only been able to cover about 2/3 of our PPM scouting acres so far this week.

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    At least while dodging mud we have been able to sample from Abernathy to Tulia and Claytonville to Edmonson. From what we have covered combined with a touch of estimation, I feel that the majority of our cotton acres have reached absolute cut-out of 3.5 NAWF or less in the last seven days.

    We still seem to have 10-20% of our fields not at that point yet with most of those still coming in at over 5 NAWF. With the average last effective bloom date of August 24 quickly approaching and the last bloom ‘guaranteed’ date in the rearview mirror, we have some management decisions to make and extra factors to consider on those late fields.

    Our main scouting focus has been on bollworms. This is despite the low moth trap catch numbers, which have not truly been matching what we are seeing in the fields lately. Although we found a light egg lay in most fields last week, worms remain comparatively hard to find. The number of fields where eggs have been found is also down this week with only about 1/4 of our fields sporting eggs or measurable damage.

    Our highest bollworm population so far has only been 5,650 small bollworms per acre in non-Bt cotton in the southeast corner of Swisher County but has been almost copied in select fields across the area. This is below our threshold of 8,000 to 10,000 worms per acre or the 6% harvestable boll damage threshold but could be getting close for a field judgement that fudges the threshold down for $0.90+ cotton.

    If you are doing this practical adjustment in your field, I do urge you to be realistic in treatment decisions as we usually experience very high mortality in bollworm eggs and young worms in West Texas. A good number of our eggs never hatch, and many young worms never live to become medium sized worms in most years.

    This is one reason we never spray for eggs in West Texas but rather walk the line to make the worms prove they will actually be an issue and catch them before they cause economic damage. With the beneficial population we are seeing, this mortality seems be even higher this year. For a few more details about bollworms this year, please note the bollworm scouting and result section farther on in this newsletter.

    Bollworms are certainly not the only pest of issue or note this week. Lygus have been popping up in most of our field counts with one field surprisingly reaching threshold and requiring treatment. While some natural fruit shed can be expected near and behind absolute cut-out, this population was feeding on and causing drop of fruit that would and should have made it to harvest.

    Bolls should be safe from Lygus once they reach the 750-heat unit level of development. Stink bugs have still been turning up on most fields again this week too. One field was high enough we initiated the boll dissection scouting to determine if they were causing enough damage to justify treatment, which in this case they were not.

    Cotton aphids remain in most of our cotton fields, but mostly only at notable levels north of Hale Center. In most southern Hale fields, the aphid populations warranted official per leaf counts. Our highest count only added up to 3.78 aphids per leaf with ET being 50-100 in pre-open boll cotton.

    I am aware of a few southern area fields that have required treatment for aphids already. For official management guidelines for these, or any cotton pest, please consult our Managing Texas Cotton Pests Guide.

    This year again we are working with BASF on a local Bt Sentinel Plot are near Aiken, Texas. The purpose of these plots are to monitor bollworm efficacy of the various Bt traits in cotton nationwide with multiple locations. It offers us an outstanding opportunity to see first hand just what impacts Bt trait resistance is having in our fields and can offer suggestions on management.

    We have been recommending that we scout all cotton fields for boll-worms regardless of Bt trait. This is the reason why. While no trait has reached ET yet in these West Texas plots, the relationship in terms of level of control between the traits is following a the same pattern as in heavier bollworm pressure areas with no control being absolute.

    Corn

    Corn held plenty of surprises for us this week too. Our oldest corn field is entering its second week of dent and should be setting a starch line soon while our youngest fields are still V10-V11, but we have a large cluster of fields between silk and early dough. With just a few weeks left of pest susceptibility, our oldest field withstood a major increase in disease and Banks grass mite pressure this week, both to near threshold levels.

    It was not alone as all our fields north of Plainview through Swisher that are post tassel stage experienced the same jump. With humidity and early morning dew, the spread of disease is expected, and it seems a bit surprising we have not experienced more issues. This likely has to do with spore availability but varietal resistance could be lending a hand too.

    The increase in mite was not expected as the same increase in corn disease should help spread diseases that aid in mite control. This week I noted no fungal issues impacting these mite populations but mite specific predators are responding. All field have a chance to remain below economic levels but I expect some fields will need to be treated with fungicides or miticides or perhaps both soon.

    Sorghum

    This week our oldest sorghum is in dough stage and starting to show some color in the grain while our youngest is way back in the vegetative growth stages. Sugarcane aphids remain the talk of the town but beneficials are steadily slowing their population increase this year. We have treated a few more fields as they reached ET this week but are carefully able to hold off on several other so far.

    Headworms continue to be fairly easy to find in headed sorghum and FAW damage in whorl stage sorghum remains common but their numbers have slacked slightly with a few exceptions. We did treat a 45% bloom stage field for a mix of headworms (0.67 medium worms per head/ 0.8 small worms per head), sorghum midge (0.44 midge per head), and SCA (48.2% infested plants).

    Individually only the SCA were above ET, but combined the midge and worms needed to be treated, especially with the expected price of sorghum. BGM increased in most fields and remains a concern. All of our SCA treatments have been ultra-successful so far. In treated fields with solid SCA control, most beneficials have been able to switch pests and help hold the mites in check.




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