As we approach the end of August, one question that has been received lately more often than any other is at what stage do I stop worrying about insects in cotton?
The major insect activity that I am noticing at this stage is around lygus bug and stink bugs.
Stop sampling and treating for lygus bug when cotton accumulates 350 DD60 (degree days 60) beyond five nodes above white flower (NAWF). The window of vulnerability for developing cotton bolls to lygus bug damage is significantly less after ~8 days post-anthesis when the carpel wall has become sufficiently thick and mature that probing activity is less damaging. Lygus bugs will continue to feed on squares and small bolls in the plant terminals even beyond 5NAWF+350 DD60 but those fruiting structures will not contribute significantly towards the yield (not to the extent to offset the cost of an insecticide application). Same applies to bollworms. Fields that have reached 5NAWF+350 DD60 are no longer susceptible to small (d•1/4 inch) larvae. This time frame may widen for larger worms but if you are not picking up on any bollworm activity at this stage, it is very unlikely they will appear from somewhere and reach damaging levels anymore.
Stink bugs, on the other hand, will have to be scouted for a bit longer. They prefer larger bolls (about quarter size diameter) and may need treatment up to 450 DD60 after 5NAWF. Once the cotton reaches 450 DD60 beyond 5NAWF, sampling and treating for stink bugs may no longer be necessary since bolls produced after this point will not become fully mature or contribute significantly to the crop yield. Now, it is possible that this value may shift slightly due to factors such as boll shading, variety, irrigation, presence of pathogen (e.g., boll rot) but it shouldn’t change to the extent that we need to keep scouting and spraying going into mid-late September or October. As per the recommended threshold, we will have to hit 50% boll damage going into 8th week of bloom to trigger a spray and the 8th week of bloom wouldn’t go beyond August.
We have had instances in the past where stink bug damage (hard locks) was found in harvestable bolls in October—this scenario would be most likely from the earlier infestations that went undetected.
CROP & PEST SITUATION Cotton Insects This year, on average, we reached 5 nodes above white flower (NAWF) on or near August 5. Which by my standard is the ideal date for our area. Based on my data as the Levelland National Weather Service Observer for August 5-23 we have accumulated 405 heat units. So, by this next week (August 26th ) a majority of the cotton acres in our program area from Ropesville to Morton and north near Littlefield will have sufficient heat units to meet the criteria of 5 NAWF + 450 DD60 Heat Units to be safe from economic insect damage. The exception to this is cotton aphids. I will continue to watch cotton aphid for some time. So, this is not the “all clear, everyone walk away from the cotton” signal. However, the signal to be very careful in spending money to control an insect situation that will not return in final yield has been given.
Cotton Nematodes Now is an excellent time (albeit dry) to soil sample for cotton root-knot nematodes. Soil sampling is important in determining populations of plant parasitic nematodes capable of reducing yield. Nematode samples collected prior to harvest may give the best estimation of nematode populations. In collecting soil samples, several factors, such as sampling method( s), sample preparation and handling and field conditions must be taken into consideration.
Several methods can be used in obtaining soil samples. Samples should be collected following a random, crossing, or zig-zag pattern (Fig. 1). A total of three composite samples (from 1/3 of the field each) should be collected per field. Additional samples may be required if dealing with different soil types in a field. A composite sample consists of 15 to 20 soil cores taken from a depth of 12inches using a soil probe, or a narrow- bladed shovel. Samples should be taken within a 4-inch radius of the taproot, as it is important to have root fragments present in the sample. The soil cores should be placed in a bucket and thoroughly mixed, being sure that any dirt clods are broken-up. A sub-sample of 1-quart should be placed in a sealed plastic storage bag. Nematode samples need to be kept cool (not frozen), and out of direct sunlight. In addition to the collection and handling of samples, field conditions at the time of sampling may impact test results. Close attention should be paid to the amount of soil moisture at sampling. Samples should not be taken if the soil is too wet or too dry.
Samples should be sent to a qualified laboratory capable of making microscopic evaluations to determine populations.
Grain Sorghum Sorghum aphids, cornleaf aphids, and headworms can all be found in area fields. The cornleaf aphids have been good fodder for beneficials to establish on. Between these beneficials and the heat sorghum aphids and headworms have had a hard time of it. However, each field is different and must be scouted to determine if these pests warrant treatment based on thresholds.
For more information on managing cotton insects in Texas go to: https://lubbock.tamu.edu/files/ 2022/07/managing-cotton-insectsin- texas.pdf For more information on managing sorghum insects in Texas go to: https:// extensionentomology.tamu.edu/ files/2019/02/Managing-Insectand- Mite- Pests- of- Texas- Sorghum- ENTO-085- 2018.pdf
ELMLEAFBEETLES
Well, lot of folks have been asking about the elm leaf beetle damage which has occurred on most all elm trees (with some exception to the lacebark and cedar elms) here in Levelland and all the South Plains of Texas. These beetles have been present for many years and have caused much damage in the past. However, I have never noted it to be as bad as it is this year. Most years a good cold winter will knock their overwintering numbers back considerably. The damage we are seeing presently would tell me last winter had little or no effect.
Adults are about 1/4 inch long and light yellow to brownish green. Several black spots decorate the head and thorax, and a broad black stripe follows the outer margin of each wing cover. Overwintering adults are darker and duller than summer adults. Eggs are laid in clusters of five to 25 on the undersides of leaves; they are yellow- orange and pointed on the outer end, resembling miniature lemons. The newly hatched larvae are black. Mature larvae are pale yellow with two black, interrupted stripes down the back; they are about 1/2 inch long. Pupae are 1/4 inch long and bright orange yellow with scattered black bristles.
Elm leaf beetles overwinter as adults in any sheltered, dry place that gives them protection. Overwintering adults sometimes enter homes, where they become a nuisance on warm days. The insects do not infest food or other household materials, but simply spend the winter indoors. In spring, beetles fly to elm trees shortly after foliage emerges. They eat holes in new leaves and soon deposit eggs. A single female may produce as many as 400 to 800 eggs. Slug-like black larvae hatch in about a week. The larvae feed for about 3 weeks on the undersides of leaves; when mature, they crawl down the tree to gather in large masses at the base of the trunk (or any other nearby, sheltered place) to pupate. Adult beetles emerge from pupae about 2 weeks later. Three or more generations occur each year in Texas. In late summer and early fall, the adults begin to seek overwintering sites. Elm leaf beetles feed exclusively on foliage. Adult feeding causes small, circular holes in leaves. Larval feeding removes most of the green material from leaves, leaving them dry and brown with only the leaf veins remaining. Heavily infested trees have sparse foliage; remaining leaves are riddled with holes, have a rusty, reddish-brown tint and are likely to drop prematurely. Severe infestations for several consecutive years can cause limbs or the entire tree to die.
Siberian elms are most severely attacked by elm leaf beetles and most of the damage is caused by first generation larvae.
Young, developing leaves provide high quality forage for the small beetle larvae. By the time the second generation is feeding, the leaves are mature and there is less damage. Generally, the environmental conditions under which second and third generations develop are not as good as those for the first generation. Elm leaf beetles do not transmit Dutch elm disease.
Natural enemies include birds, toads, diseases and predaceous and parasitic insects. A small wasp frequently kills many pupae. A fungus also kills pupae and adults late in the summer, especially if the weather is humid. Unfortunately, these natural controls are not often sufficient to hold the beetles in check, so it is necessary to use insecticide.
Early detection of the beetles makes it possible to spray trees before much damage occurs. Examine the undersides of leaves for yellow eggs and young larvae soon after leaves emerge in April. Apply insecticides when most of the eggs have hatched and the small larvae are just beginning to feed. Make sure insecticide thoroughly covers newly developing leaves. It may be necessary to hire a commercial applicator, someone who is properly licensed and equipped, to spray tall trees. Insecticide applications may need to be repeated to control later generations of beetles.
Another approach is to use systemic insecticides, which can be applied as tree implants, soil injections or granules. Systemic insecticides are transported through the tree to the leaves. To control the first generation of beetles, a systemic insecticide should be applied in late March or April.
Adult beetles can be excluded from homes by placing tight-fitting screens over windows and doors and closing all other openings. Spraying outside walls and the perimeter of the house with properly labeled insecticides may reduce the adult population in the fall.
If you have specific questions about these insect pest or their control give me a call at 806 6385635 or go to: https:// agrilifelearn.tamu.edu/s/product/ elm-leaf-beetle/ 01t4x000004OUV9AAO and download an excellent Extension publication on this subject (includes insecticide recommendations).