Texas Plains Cotton: Insect Populations Continue to Rise

Tarnished plant bug, aka lygus bug. Photo: Lisa Ames, University of Georgia, bugwood.org.

Most of our surviving crop acres are in either “crunch time” or along one or another side of it. This terminology for me means peak water use and peak fruit set or grain fill. Where any individual field currently sets depends mostly on the spotty rainfall events of last week and irrigation capacity, but also planting date.

In our scouting program, we are considering various pest situations, plant growth regulators, the last of our heaviest irrigations, and even alternate uses of a field in some desperate cases. Field situations vary greatly.

Pest populations continue to rise, but rarely to economic levels still, with some obvious exceptions. Some of the drier fields may only have a matter of weeks of pest susceptibility left, while others have a long way to go.

Weed pressure is a mixed bag depending upon timeliness and aggressiveness of residual applications. The 2020 growing season continues to present every challenge it can.

Cotton

This week our PPM program cotton ranged in stage from 9/10 grown square wildcat cotton up to absolute cut-out setting the last of this season’s bolls. Most fields fell between 5.4 NAWF and absolute cut-out of 3.5 NAWF with a solid group of slightly late planted outliers grouped around 6.5 NAWF.

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All relevant pest populations increased again this week. Fleahoppers even became an economic problem in our wildcat cotton causing a heavy increase in what should be harvestable fruit. Lygus were found in all but a few fields.

A few more bollworm eggs were spotted, several foliage feeding pests, cabbage loopers with a few beet armyworms thrown in, were found in all non-Bt fields, stink bugs found in about 10% of our fields, and a few stray cotton aphids and two-spotted spider mites were noted.

It is possible that any one of these pests could become problematic soon. For a comprehensive guide to managing any of these pests, please consult out Texas A&M AgriLife Extension Cotton Insect Guide.

Of these pests, only Lygus presented economic situations for us in blooming cotton this week. Much like the past few weeks, only a few fields were problematic. In these fields, Lygus nymphs were the bulk of the population.

These nymphs seem to have been the direct result of a borderline adult population that passed through our fields a few weeks ago, leaving a subsequent population behind that was heavy enough to cause excessive fruit drop issues. The ET for Lygus remain at 1 Lygus per 2.5 row feet with proven fruit loss.

This should increase as cotton nears the end of the season. Squares and bolls remain susceptible to Lygus damage until the boll has accumulated about 750 heat units. As bolls mature and more and more reach this milestone in their development, less and less fruit per plant can be damaged by the Lygus.

Shortly after absolute cut-out, this Lygus ET can drop to 1 Lygus per 1.5 or even 1 per row foot. Plants at and after absolute cut-out also experience quite a bit of natural fruit shed. Decision makers should be careful with Lygus issues in fields in this situation.

Lygus feeding on fruit that is being aborted naturally anyway because the plant cannot hold any additional bolls is not an economic concern.

The very few bollworm eggs we found in cotton this week were the exception and not the rule. Our highest counts came in at only 4,312.5 eggs per acre and no worms or worm dam-age was found. All fields where eggs were found were on the lusher side of the area’s cotton and were also not near any acceptable corn field for the moths to settle in.

This might change as/if moth populations continue to increase through August and corn matures. Before and if bollworm decisions are made this year, the field conditions should be considered for this pest also. Bollworms will have a hard time establishing in fields with nothing but large bolls from bottom to top.

Much like Lygus feeding, bollworm feeding upon fruit that will be shed naturally does no economic damage but could allow them to develop into a larger worm that might later damage larger bolls if no beneficials are available to control the worms.

Fields still at 6 NAWF or later may remain susceptible to worm damage for the balance of the month.

We also noted a few more fields exhibiting verticillium wilt symptoms this week. While there remains little that is proven to help once vert symptoms show, I urge growers to take advantage of the situation to evaluate the level of vert pressure so that educated off-season management can be made.

Corn

Our program corn ranged in stage from early tassel to dent stage this week. Spider mites, namely Banks grass mites (BGM) were our main pest of concern, not taking into consideration environmental conditions. Generally speaking, the BGM increased this week, but it was not a steady pressure.

In fields where they were found in numbers last week, rains and dew-filled mornings aided in mite diseases and predators crashing most populations while in fields where BGM were hard to find last week, mites increased to perplexing numbers.

None of these situations were economic with our highest field rating on our 0-10 A&M mite rating scale being 2.7 with 3.5-4 being economic. Bollworms/corn ear-worms, rarely if ever an economic concern in field corn, remain fairly easy to find in tender ears.

Still, worms are not present in all ears yet, indicating an overall light pressure so far. No western bean cutworms or fall armyworms have been found in our corn ears so far.

Sorghum

Our sorghum ranged in stage from V6 to soft dough this week. Sugarcane aphids (SCA) remain our main pest in sorghum today. We have not had any field reach ET yet, but populations increased steadily in headed sorghum, creeping upward with good beneficial interference. We still have not found any SCA colonies in whorl stage sorghum yet.

We did find a few more bollworms/headworms in our sorghum, this week but they were well below ET here also with our highest pressure being 5% of the heads infested with small worms. BGM increased in most post boot fields as well, with our highest population rating a 1.9 on the 0-10 scale.

Fall armyworms continue to be common in all whorl stage sorghum with all our PPM fields being well below ET. We are officially past the average sorghum midge arrival date for the Plainview area of August 4th, but we have still not seen any midge in our blooming fields.




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