Cotton on the Texas High Plains: Watch out for Bollworm Activity

Suhas Vyavhare, Texas A&M AgriLife Extension Service

Insect pressure remains light in most parts with cotton ranging from 5 nodes above white flower to hard cutout. We are seeing conchuela stink bug population reaching economic threshold in few fields in Crosby County. However, the infestation is much localized and it is unlikely that we will see economic stink bug infestations in cotton in other areas of the High Plains. I often encounter a few lygus adults and nymphs but the numbers remain well below economic threshold. At this point, one insect that is on our radar is the cotton bollworm. Although much of our cotton has cutout hard and is becoming non-attractive to worms, there are still enough suitable cotton fields out there to worry about.

Earlier this week, Brad Easterling, IPM-agent in Glasscock, Reagan, and Upton counties reported above threshold levels of bollworms in Bt cotton fields near Garden City. Blayne Reed, IPM-agent in Hale, Swisher, and Floyd counties reports that he is seeing increased numbers of bollworm moths in his pheromone traps (http://halecountyipm.blogspot.com/2016/08/late-august-2016-bollworm-threat.html). With the corn and sorghum maturing, we may see increased bollworm movement out of corn into cotton in the next few weeks which makes regular scouting for bollworm larvae essential.

Please report any signs of higher than normal worm damage in cotton (especially Bt cotton) to me at 806-723-8446. We can visit a field and collect insects for resistance and/or old world bollworm screening.

Bollworm larva

When scouting, make sure you do whole plant inspections (squares, white blooms, pink blooms, bloom tags and bolls) for bollworm larvae and injury. Make sure to inspect at least 100 randomly selected plants covering all major areas in the field. Bt toxin is not well expressed in the flower tissues, and as a result bollworm larvae can often be found associated with pink blooms and bloom tags. One should be careful about not oversampling bloom tags while scouting Bt cotton fields. Also, remember bollworms must feed on the cotton plant before they ingest a lethal amount of the Bt toxin, so 1^st instar larvae (<1/8-inch) should never be used as a trigger point to spray.

It is often hard to control bollworms with foliar insecticide application once larvae grow larger than ½-inch long. Therefore, it is important to spray for larvae when they are still smaller. If treating a bollworm population that is actively feeding on bolls, consider using a long residual contact insecticide that the worm is more likely to become exposed to when moving from one boll to the next. When targeting bollworms, pyrethroids with good cov

Bollworm damage

erage can still do the trick. However, if fall armyworms are present, the product choices may differ as pyrethroids are weak against fall armyworm, especially larger larvae.

Once cotton plants have an average of 3 nodes or fewer remaining above the uppermost first position white bloom or when the upper bolls that will be harvested have become difficult to cut with a pocket knife, they are normally safe from bollworm injury.

Here is a link to our new video on scouting for bollworms in cotton. (https://www.youtube.com/watch?v=vJhTJ9doDSw) 

Whole plant inspection method: bollworm action threshold based on number of larvae per 100 plants
		Cotton type
Cotton stage	Worm size	Non-Bt	Bt
Before bloom	All	≥30% damaged squares and worms are present
After boll formation	≤1/4 inch	10-15 worms per 100 plants	Do not treat
	>1/4 inch	8-12 worms per 100 plants	8-12 worms( >0.25 inch) per 100 plants with >5% damaged fruit
Fields that have accumulated 350 DD60s beyond 5 NAWF are no longer susceptible to first or second instar bollworm.

                                  

Sugarcane aphid update and conditions for using Transform insecticide

As of this writing on Friday, August 5th, sugarcane aphids have been found over much of the Texas High Plains. Tommy Doederlein, Extension IPM Agent in Dawson and Lynn counties, raised the alarm on Monday. Today we know that fields in Floyd, Crosby, Lubbock, Hale and Hockley counties have required insecticide applications. In the northern Panhandle the aphid has been found as far north as Perryton and as far west as Bushland. We are seeing abundant winged adults, so it goes without saying that sugarcane aphids could be anywhere on the High Plains.

Scouting procedures and treatment thresholds are presented in our 2016 sugarcane aphid publication. There are only two good insecticides for sugarcane aphid control; Sivanto and Transform. By "good" I mean high efficacy with little effect on beneficial insects. Sivanto has a full label and Transform can be used through its Section 18 label. This puts some additional restrictions on Transform use, although they are not onerous. Dr. Ed Bynum summarized the conditions of the Section 18 label in his newsletter today, and here is what he said.

"The Section 18 Emergency Exemption label for Transform has some specific information regarding application use and application restrictions. A COPY OF THE LABEL MUST BE IN HAND WHEN APPLICATIONS ARE MADE.

Here are some of the specifics from the Texas Section 18 Label. However, be sure to read the label before applying.
 • Rate range: 0.75 to 1.5 oz. per acre.
 • Application by ground or air (no chemigation).
 • Wind speed not to exceed 10 mph.
 • Droplet Size: Use only medium to coarse spray nozzles (i.e., with median droplet size if 341 μm or greater) for ground and non-ULV aerial application according to ASABE (S 572.1) definition for standard nozzles. In conditions of low humidity and high temperatures, applicators should use a coarser droplet size except where indicated for specific crops.
 • Boom height for ground application: Not to exceed 4 feet.
 • Carrier volume for ground application: A minimum of 5 to 10 gallons per acre - to be increased with increasing crop size and/or pest density.
 • Carrier volume for aerial application: A minimum of 3 gallons per acre, but a minimum of 5 gallons per acre is recommended.
Restrictions:
 • Preharvest Interval: Do not apply within 14 days of grain or straw harvest or within 7 days of grazing, or forage, fodder, or hay harvest.
 • A restricted entry interval (REI) of 24 hours must be observed.
 • Do not make more than two applications per acre per year.
 • Minimum Treatment Interval: Do not make applications less than 14 days apart.
 • Do not apply more than a total of 3.0 oz of Transform WG (0.09 lb ai of sulfoxaflor) per acre per year.
 • Do not apply product ≤ 3 days pre-bloom until after seed set."

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The final bullet point about restricting Transform use from three days before bloom until seed set is there to protect honeybees. Extension IPM personnel were asked to make note of honeybees in blooming sorghum this year, so I have been paying close attention. Well, I am highly allergic to bee venom and I always pay close attention because I'm not ready for mortality quite yet. My observations on the AgriLife Research and Extension Center at Lubbock have been that it is very common for large numbers of honeybees to visit sorghum. This usually occurs early in the morning prior to 10:00 am. After that time I seldom see honeybees in blooming sorghum fields. When I get more time I may post video of honeybees in sorghum.

Large Fall Armyworm Flight Underway (8/1/2016, Updated 8/4/16)

Pheromone trapping at the AgriLife Research and Extension Center in Lubbock indicates an unusually large flight of fall armyworm moths is underway. Fall armyworm and corn earworm comprise the "headworm complex" in grain sorghum. Our research in 2011 and 2012 indicated that fall armyworm larvae cause an average per ear loss of 0.2 lbs of yield in non-Bt corn when they puncture the side of an ear. The losses in corn are both from direct kernel feeding and the introduction of fungi that destroy an approximately equal number of kernels.

We normally report trap data on Wednesday but, given the high numbers of moths captured, today's graph (Monday) projects the weekly capture based on 5 of seven nights.

Update on 8/4/16: Here is the official chart which represents a week's worth of moths captured.