Critical Period for Bollworm Escapes on 2 Gene Cotton in AL

Ron Smith

Extension Entomologist, Auburn University

We are entering the most critical period of bollworm presence during the next 20 days (July 15-Aug 1). This increase in bollworm activity began last week (July 9-13) along the Gulf Coast and the Mobile/Santa Rosa County (Jay) FL area. By July 20^th, we should see an increased bollworm egg lay in Central AL (Montgomery, Prattville, Selma areas). By the 25^th this increase may reach Cherokee County in the northeast, and by August 1^st the Tennessee Valley area of northern AL.

Increased bollworm moth presence was noted last week as far north as Pike and Barber County (Troy) area. This increased moth activity will be influenced by the planting date and acreage of corn planted in a given region of the state. Most all bollworm were corn earworms in corn previous generation. This life cycle is about 30 days and the eggs in corn were deposited during the white or pink silk stge. About 30 days later these moths that emerged from corn are looking for their next host. Cotton is the best host they will find in AL (not soybeans or peanuts).

Many (but not all) fields in all areas of the state had more worm damaged bolls in 2017 than we had seen since 1995. If we want to prevent this from happening again, the next 2 weeks are critical.

I assume that most realize now that our 2 gene cotton has lost some level of effectiveness against the bollworm species. When resistance is a factor, the problem usually gets worse over time—it seldom gets better.

Now, what should fieldmen be looking for?

1.     Eggs in terminals or on the fruiting structures: square bracts, white or red blooms (threshold on 2 gene cotton is 20 eggs/100 plants)

2.     Damaged squares in the upper canopy – may find more damage to small squares near the terminal in Phytogen varieties (5% damage is threshold).

3.     Newly hatched larvae

May find in small squares in Phytogen varieties

May find more in open white blooms or underneath red or dried blooms in Delta Pine and other varieties

(5% of plants with small larvae is threshold)

These small larvae are white when they have just hatched and will turn pale green within a day or so.

One thing that makes them stand out in a white bloom is they will have a black or dark brown head. Often the head is the best thing to look for since being dark stands out from the white bloom petals. (See Picture)

Once a significant increase in eggs or small larvae are detected—do not waste more time in the field. Get the word to the grower and get the sprayer loaded. Every 24 hour period that passes from detection to treating means less effectiveness with your insecticide. Also note that these bollworm moths will likely seek out our oldest and most promising cotton to deposit eggs in.

Now what treatment options do we have? Basically two. We can try the older chemistry, pyrethroids, or we can go to the newer chemistry, Besiege and Prevathon.

Things to consider here: bollworms have shown levels of resistance to pyrethroids in many areas of the cotton belt. However, the pyrethroid chemistry is much less expensive. Pyrethroids have about a 4-5 day residual on bollworms, where they are still active.

The newer chemistry Beseige and Prevathon have about 10+ days of residual on bollworms, depending on the rate applied.

If using pyrethroids, I suggest the highest labeled rate. If using Beseige, I suggest 8-9 oz/ac. If using Prevathon, I suggest 16-18 oz/ac. Besiege contains a low rate of Karate pyrethroid in the mixture. If you need tarnished plant bug or stink bug control, you will need to add about 1 oz of additional Karate, or equivalent pyrethroid, to the tank mixture. Prevathon has no activity on plant bugs or stink bugs.

In summary, this is the time to be ready to react to bollworms in 2 gene cotton. I will be tweeting as I hear of increased pressure in a region, county, or area.

I will be conducting tests on thresholds, timing, and chemical choices at our research farm at Prattville in Central AL, so will be in the field a lot within the next 2 weeks or so.

Stay in touch with the Syngenta Pest Patrol reports for up to date observations on bollworms. To sign up for the Syngenta Pest Patrol Updates for Alabama, register online at syngentaus.com/pestpatrol or register via text by texting pestpat11 to 97063.

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Thoughts and Tips for Bollworm Scouting on 2 Gene Cotton for 2018

          If you had an economic problem with escape bollworms on 2 gene cotton in 2017 and anticipate the problem in 2018, consider a 3 gene variety. Select one with similar maturity and yield potential as those you've been planting. This reduces acres scouts/consultants must focus on escape worms.

         When planting 2 gene cotton in 2018, monitor for bug and sucking pests and only make in-season foliar sprays when economic damage is found. This will conserve beneficial insects and reduce escape bollworms.

          If monitoring 2 gene cotton in 2018, take note of the corn planting window in your area. This plays a large role in the emergence & movement of corn earworm (bollworm) moths to cotton in July & Aug. The more corn planting is spread out, the wider the emergence window of bollworms.

          Bollworm moth activity isn't constant throughout the season. Instead it occurs in cycles especially through July. By August, generations of bollworms & tobacco budworms overlap. Fieldmen should detect the start of these peaks by focusing on eggs & newly hatched larvae in terminals/white blooms.

          Based on my observations during the Bt cotton era of the past 20 plus years, escape bollworm larvae do not feed on or damage as many fruiting sites per worm as they did in the pre Bt era.

          Scouting intervals for bollworms should be reduced to 3-4 days during critical windows on 2 gene cotton in 2018. Fieldmen may monitor select sentinel fields of similar variety and planting date to detect increased activity.

When monitoring for bollworm larvae or eggs on 2 gene cotton in 2018, be more concerned about detecting population increases early, and reacting if necessary, than quantifying exact numbers-- for example: 18 vs. 28 per whatever.

Fieldmen should consider damaged fruit on 2 gene cotton in 2018, but treatment decisions will be more timely if primary focus is on eggs and/or newly hatched larvae.

In order to stay on schedule in 2018, fieldmen should consider only staying in a field long enough to make a confident treat or not treat decision.

          Pest Patrol Updates on crop insects in Alabama available again in 2018. These alerts, sponsored by Syngenta, are beginning their 10th consecutive season. University entomologists discuss current conditions and advise on insect management.

        To sign up for the Syngenta Pest Patrol Updates for Alabama, register online at http://www.syngentaus.com/pestpatrol  or register via text message by texting pestpat11 to 97063.

Late July/Early August Cotton Insect Situation in Alabama

What are we currently finding in Alabama cotton fields? Plant bugs, both the tarnished and clouded species, have finally reached threshold or treatment levels in April planted fields that have not been sprayed. Some level of brown stink bugs can also be found in these same fields. A bug clean up spray would be advised for most cotton that is in the fourth or fifth week of bloom. Peak numbers of squares and bolls are currently at risk. Cotton planted after about May 10 missed most of the plant bugs this season. In central and south Alabama, there are very few plant bugs currently present in wild host or other crops. In other words, there are no more plant bugs in the landscape to migrate to cotton in 2017 in that region.

Between July 24 and 28, numerous field people from all areas of the state were contacted about escape bollworms on cotton with caterpillar technology. As of July 31, no none has reported any problems. We have conventional cotton on research stations in several areas of the state. Some level of bollworms and damage can be found on this cotton. The corn earworm flight from corn began about July 15 and has likely already peaked. Tobacco budworms will enter the mix during the month of August, but they will not be part of the "escape" situation in August. However, fieldmen should continue to monitor closely for escape bollworms. In Alabama, I would suggest we try the pyrethroid chemistry first if escapes are found.

Spider mites came into the picture about the third week of July in the Tenn. Valley area. Mites will likely show up in other fields statewide if we ever experience a 7-10 day period between rain events. Abamectin will provide the most economical control of mites. Whiteflies may occur in late season on our late maturing fields. If whiteflies are observed, I would recommend we use pyrethroid chemistry for stink bugs since Bidrin seems to aggravate the whitefly situation.

We will likely see stink bug numbers increase as we move into August and even September in our late maturing cotton. The southern green stink bug will make up a greater part of the population in coming weeks. This gives us the flexibility to choose either pyrethroid or phosphate chemistry. For weeks 3 through 6~7 of bloom, we recommend a 10% internal damage boll threshold for stink bugs.

Thus far in 2017, insects have not been a major limiting factor in Ala cotton production. Let's hope we can keep this trend going for several more weeks.