Bollworms per acre coming off of corn (or why we had fewer bollworms this year)

Dr. Suhas Vyavhare and I are conducting a very detailed experiment this year on some aspects of Bt corn. Part of the experiment involves putting 120 emergence cages on the ground under corn after corn earworm larvae (cotton bollworms) have left the corn ears and entered the soil for pupation. This lets us determine the number of moths being produced per square foot or acre under actual field conditions. After they emerge as moths, these insects will then fly to other crops, and their eggs become the late season bollworm infestations in cotton and headworm infestations in sorghum. 

2020 was a fairly light year for corn earworm infestation in corn; only 54% of the ears were infested with larvae at our Olton trial. In most years this would have been nearly 100%.

Here is the math: 

This year we had 3,398 moths emerging per acre from irrigated non-Bt corn, or 407,760 moths per 120 acre field.

In a "normal" year when almost every ear had a corn earworm, this would have been 6,292 moths per acre, or 755,040 moths per 120 acres of irrigated corn. 

My work with the older Bts like Cry1Ab, Cry2Ab2, Cry1F and Cry 1A.105 suggest these Bts are no longer killing as many earworms as they once did, so one could expect them to produce a significant number of moths. Vip3a corn is highly effective at killing corn earworm, so it will not contribute significantly to a moth flight (until we get resistance). 

This is the first chance we have had to estimate the number of cotton bollworm moths coming off of corn on the High Plains, and the numbers are impressive, at least in their contribution to localized bollworm populations in nearby cotton. The lower number of bollworms this year in cotton seem to be directly linked to the lower number of bollworm moths that laid eggs in corn. 

Sesame Leafroller Now Widespread on the High Plains

Sesame leafroller is a major pest of the crop, and we have tracked its movement north this year. This is a new pest for us. Dr. Emi Kimura, our agronomist in Vernon, reported it last week. This week Drs. Qingwu Xue and Jourdan Bell reported it at Bushland, and one of our superb Independent Crop Consultants reported it at Abernathy just north of Lubbock and made comment that he treated the field three weeks ago and now had to treat again. He also just today reported it near Gruver in the northern Panhandle.

Dr. Holly Davis, Extension Entomologist in Weslaco, recently posted a nice blog article and video on sesame leafroller, so I won't duplicate that information here. She conducted an insecticide efficacy trial which showed pyrethroids don't work all that well. She also found that the 8 oz and 12 oz. rates of Prevathon worked very well, and the 8 oz rate did just as good a job. (The difference will be that the 12 oz rate will provide longer residual control.) Blackhawk also worked very well at 1.1 and 2.2 oz, but Blackhawk is not labeled for use on sesame. 

Here are some photos from near Abernathy today.

South Plains cotton: questions related to Lygus bug

 At what stage cotton is safe from Lygus bug?

No treatment is needed once cotton reaches 350 DD60s beyond cutout (5 NAWF).  

 What is the threshold for Lygus bug after peak bloom?

Use of drop cloth is the best way to measure plant bugs after peak bloom. Treatment thresholds based on drop cloth sampling is 4 to 6 Lygus bugs per 6-foot row.

 What insecticides to use to manage lygus bug in cotton?

Below is a table with the list of suggested insecticides. Add Transform to the list.

 

Would these products provide control against stink bugs too?

Acephate and Bidrin has a good activity against stink bugs. However, other plant bug products alone (e.g. Transform, neonicotinoids) will only provide some level of stink bug suppression and will not be enough to effectively control them.

Tip: Do not confuse seed bugs or scentless plant bugs with Lygus. Although fairly common, scentless plant bugs feed mostly on weeds and are harmless to cotton.  

 

Lygus bug (photo: Pat Porter) 

Scentless plant bug 

Texas High Plains cotton: stink bug remains quiet

Cotton fields that have accumulated 450 DD60 (degree days 60) beyond cutout (5NAWF) are generally safe from an economic damage from stink bugs. Late planted and heavily irrigated fields with fairly high number of young bolls still need to be scouted for stink bugs. Stink bug feeding on young bolls (<10 days old) usually causes the bolls to shed. In larger bolls, stink bug feeding often results in dark spots ~1/16 inch in diameter on the outside of bolls. These dark spots do not always correlate well with the internal damage—callus growths or warts and stained lint. Damage to the internal boll wall is a good indication that lint and seed are affected.

Base decisions to treat for stink bug infestations on the percentage of bolls with evidence of internal damage (warts or stained lint associated with feeding punctures).  To use this technique: ◆ Remove about 10 to 20 bolls, one inch in diameter (about the size of a quarter), from each of four parts of the field, avoiding field edges. ◆ Break open the bolls by hand or cut them with a knife. Look for internal warts on the boll walls and stained lint on the cotton locks. ◆ Check bolls with visible external lesions first to determine if the internal damage threshold has been met because bolls with external lesions are more likely to also be damaged internally.

Use a 10 percent to 15 percent boll injury threshold during weeks 3 through 5 of bloom and 20-30 percent during weeks 6 or later of bloom. If using drop cloth or whole plant inspection method, detection of 1 stink bug per 6 row-feet would also justify treatment. Pyrethroids or organophosphate (e.g. Bidrin, Orthene) insecticides provide a good control against conchuela stink bug which is the primary species we encounter. Products targeted at plant bugs such as Transform, Carbine, Diamond, and neonicotinoids will not be sufficient to control stink bugs. For the mix of stink bug and plant bugs, either Bidrin or acephate would be a good choice or a tank mix of plant bug product (e.g. Carbine, Diamond, Transform, neonicotinoids) and a pyrethroid or acephate. Detailed list of suggested insecticides can be found at: https://lubbock.tamu.edu/files/2019/08/2019-Cotton-Insect-Control-Suggestions_ENTO090.pdf

Texas High Plains cotton: keep an eye out for bollworms

The current spike in bollworm moth activity in our pheromone traps is from moths coming out of corn. These moths pose a substantial threat to cotton with majority of our fields being in peak bloom. I have not noticed significant worm activity in cotton yet but last week we did start to pick some worm damage in our research plots of non-Bt cotton. The amount of fruit damage in non-Bt cotton ranges from 0-2%. This is expected to increase over the next few weeks as more moths coming out of corn land in cotton. It is important to scout cotton twice a week irrespective of Bt technology. Bt resistance in bollworm field populations being widespread, under high insect pressure we may need to spray some of our two-gene Bt fields. In all cotton (Bt or non-Bt), treatment is recommended if 6% fruit damage (mix of squares and bolls) is observed.

The diamide insecticides, Besiege (7-10 fl oz/acre) or Prevathon (14-20 fl oz/acre), are the most effective products to control bollworm. These products provide about two weeks of residual control. With higher rate, longer residual control can be obtained. If you are finding stink bugs as well, Besiege will provide control against both worms and stink bugs. However, if there are no stink bug issues, it is best to avoid unnecessary pyrethroid applications as they can flare up aphids.  

 List of additional insecticide options can be found in our cotton insect management guide: https://lubbock.tamu.edu/files/2019/08/2019-Cotton-Insect-Control-Suggestions_ENTO090.pdf

 Here is a link to our video on how to scout for bollworms: https://www.youtube.com/watch?v=ELcza4t2BYI

 

Sugarcane Aphid in Lubbock and Hale Counties (Probably Crosby and Floyd, Too)

I found sugarcane aphid colonies on post-flowering sorghum today at the Experiment Station in Lubbock. An independent crop consultant reported to Blayne Reed this afternoon that he had just found some in Hale County, about 6 miles northwest of Abernathy. So here we go.

In the last few years we have tracked the aphid's arrival on the southern High Plains, and traditionally it comes first through Floyd and Crosby counties, then to Lubbock, Hale etc. So it is most likely that Crosby and Floyd counties have it as well.

There is some good news: The aphid is a couple of weeks late in arriving, and many fields will be able to outrun it. And in what is really good news, we are not getting large flights from the south and southeast, so the invading population is relatively small, which gives the beneficial insects the upper hand for now.

I have been asked about the 106 - 108 degree days, and whether these will phase the aphid. I don't know. Drought stressed sorghum loses the ability to transpire in the hot part of the day, which means it does not have much evaporative cooling going on at the leaf surface. On days like we had today, I can easily see it being 120 degrees near the soil surface in full sunlight, and this is hot enough to affect some types of insects. Irrigated sorghum is less apt to shut down on these hot days, so it will continue to have some evaporative cooling at the leaf surface. I don't think aphids on these plants will be affected much.

Texas High Plains Cotton: Time to Guard Up Against Thrips

Cotton planters are rolling across the Texas High Plains. While lot of cotton seed will go into the ground over the next couple of weeks, some of the early planted stuff is making its way above ground. Thrips are one of the first insect pests that we experience on seedling cotton. I am seeing thrips swarms all around and can find them on almost everything that is green. It will not be too long before these tiny insects land on the emerging cotton. We usually experience higher thrips pressure in the areas north of Lubbock. Under good growing condition, plants do recover from thrips injury without economic yield loss, but when additional stresses such as cold temperatures, sandblasting and or nematodes are present, thrips infestation can delay growth and reduce yields substantially.

Thrips species composition in the South Plains region is mainly formed by onion thrips (Thrips tabaci) and the western flower thrips (Frankliniella occidentalis). Preventive insecticide seed treatments provide a good control against these species for up to ~3 weeks after planting. However, this can vary with growing conditions and the weather. Almost all our in-furrow or insecticide seed treatments used are neonicotinoids (e.g. imidacloprid, thiamethoxam). Remember, these are water-soluble insecticide compounds that are taken up through the roots and translocated into growing leaf tissues and hence need enough soil moisture to be effective.

When scouting for thrips, there is truly no substitute for whole plant inspections from a representative sample from across the whole field. We may find adult thrips (winged) in almost every field but it is important to know that presence of adults alone will not warrant foliar insecticide application. The presence of immature thrips (wingless) is a good indicator of whether the seed treatments are still effective enough or not. The action threshold for thrips is one thrips per true leaf and our suggestions as rescue treatments include acephate, dicrotophos (e.g. Bidrin) or spinetoram (Radiant). Timing of insecticide application is critical. Research indicates that insecticide application beyond 1^st true leaf stage will not result in significant yield gains. Also, remember, it is not uncommon to see “look-a-like” thrips symptoms under our environment—beware of similar symptoms from sandblasting, residual herbicides and high temperatures before making spray decisions. We cannot control the environment or the market but we sure can save money and time by avoiding ill-timed or unnecessary insecticide applications.