Extension entomologists from across the Cotton Belt expressed concern that using the three-gene Bt trait in corn could lead to resistance.

The five entomologists participating in an insect management panel discussion at the recent Cotton Consultants’ Conference, part of the annual Beltwide Cotton Conferences in Austin, Texas, also expressed optimism for new traits targeting lygus and thrips.

David Kerns, Texas AgriLife; Sebe Brown, LSU; Ron Smith, Auburn University; Angus Catchot, Mississippi State University; and Jeremy Greene, Clemson University, also talked about insect pest pressure in 2019 and what to expect in 2020.

“Using the three-gene trait in corn is a threat,” Kerns said. “We see some benefit from the VIP (vegetative insecticidal protein) trait in corn, but I hate to see it. Bt corn is driving resistance as we see an erosion of effectiveness.”

“We don’t plant three-gene corn in Louisiana,” Brown said. “We see no economic benefit and prefer to reserve three-gene technology for cotton. We don’t need VIP for corn earworm.”

“The entire panel across the Belt agrees on this point,” Smith added.

“More than 90% of the bollworm population we see in cotton in July funnels through corn,” Catchot said. “That population selects for resistance.”

He fears that continued use of the VIP trait in corn will hurt efficacy of the trait in cotton. “We don’t see the economic benefit in corn that we do in cotton.”

Look for breakdowns

Kerns encourages producers and consultants to look for breakdowns in the VIP trait as they scout cotton fields. “If you see injury on three-gene cotton, report it. It is vitally important that we know if you’re seeing it. We are not seeing it manifest in Texas cotton, but be cognizant of the possibility.”

He said the VIP trait could last for 10 years. “But if you see unusual worm survival in VIP technology, let us know about it. We would like to get collections out of it.”

They offered a more optimistic outlook for varieties containing a lygus trait, expected to hit the market in 2021 or 2022.

“I don’t expect to need the trait for lygus,” Greene said, “but it will be good on thrips, especially if we lose the neonicotinoids or if other products become unavailable.”

“We will definitely see benefits in Louisiana,” Brown said. “It works well on thrips and is a good fit for lygus.”

“This is an additional tool for lygus control,” Smith added. “It will be a nice fit in the Alabama Tennessee Valley as well as the rest of the Southeast.”

Smith added that the lygus trait may mean Southeast producers need to spray for these pests only once, “maybe not at all.”

Thrips game changer

“It’s a game changer for thrips in Texas,” Kerns said. “I’m also interested to see if it will have any effect on cotton flea hoppers.”

“The lygus trait should completely eliminate thrips sprays for plant bugs,” Catchot said. “It should at least reduce the number of plant bug sprays.”

Panelists discussed insect pest pressure from the 2019 season. Kerns said the biggest pest threat in Texas has been cotton flea hoppers. Populations in 2019 were very high. “Thrips were quite intense. And aphid infestations were the worst I’ve seen in 10 years or longer. Producers made a lot of applications. We also saw some leaf roll virus (cotton leafroll dwarf virus).”

A few bollworm hotspots showed up with some resistance issues and some break-through on three-gene cotton. “I believe that was the plant expression and not resistance,” Kerns said. He noted some issues with spider mites and stinkbugs.

“It was also a big year for grasshoppers in west Texas.”

“Our situation was similar in some respects to Texas,” Brown said of Louisiana insect issues. “We saw thrips early. Seed treatments worked well.”

He said plant bugs hit threshold in mid-season in northwest Louisiana with normal populations along the Delta. He said insecticide applications ranged from two to nine sprays.

Bollworm pressure early

Bollworm pressure hit threshold early, he said. He said producers were frustrated with consistent pressure that never quite hit threshold. “Three-gene cotton helped and we saw no issue with failure of the trait. Stinkbugs were not bad.”

“Thrips were extremely light in Mississippi on cotton planted at the normal time,” Catchot said. “They were heavy later on replanted cotton.”

He said acephate in-furrow or over-treated on the seed worked well.

“Mississippi farmers made the lowest number of sprays in a long time for plant bugs.” Catchot said. Bollworm control offered challenges. Weather-related disruption of corn planting spread bollworm moth flights over a longer than usual period. He said populations in cotton would not hit threshold but were consistent and caused damage. “The last population came out late because finally there was no more corn to go to, so we had the biggest part of our flight very late. It was hard to know what to do.”

“We saw extreme variability in insect pressure in Alabama from region to region this year,” Smith said, “sometimes even with certain species, even from field to field on the same farm. I’ve never experienced a year where insect monitoring was more important. It was not uncommon for adjacent fields to require drastically different insect management inputs in 2019.”

He said thrips came in unusually late in 2019, “about the latest we’ve ever seen and about the highest numbers we’ve ever seen. It really didn’t start until about mid-May and continued for several weeks after that.”

He said the thrips predicter model was “highly accurate” and will be a good tool in the future. “The model will change dramatically in a two-week period when it’s sensitive to thrips pressure in a dry period.”

Aphid pressure

Smith said aphid pressure was highly variable across the Alabama. “We can’t get adequate control of aphids with insecticides,” he said. “We had as many as eight sprays on some plots.”

Spider mites have been trouble in cotton for many years, Smith added, but damage was minimal during the era of aldicarb.

“At present, we’re dealing with them in most fields all season long, depending on weather conditions and what the field has been sprayed with.”

Smith said the stinkbug complex has been the most damaging pest across the Southeast for several years.

Greene said last May was the hottest on record in South Carolina and also brought on the heaviest thrips pressure he had ever seen. Acephate on seed treatments looked good, he said. “That also worked well in 2013. In-furrow acephate treatments also worked.”

He said aphid pressure was high and cotton leafroll dwarf virus was widespread across the state. Plant bug pressure, primarily tarnished plant bugs, caused some problems in some fields, he added, but were not an economically significant pest statewide.

“We had some of the lowest bollworm pressure we’ve ever seen in research plots, but we did have reports of breakthroughs on two-gene Bt cotton. Pyrethroids are not as good as they used to be to control escaped bollworms in cotton, but we need them for stinkbug control.”

He said stinkbugs are the primary pest complex in corn but “did not hurt us as bad in cotton.”

2020 management

Entomologists said experience from 2019 might be useful but can’t serve as a roadmap to prepare for 2020 insect management.

“I like to go into the season with a plan,” Smith said, “but due to planting date and weather conditions, you have to adapt your plan as you move through the season.”

“In 2019, bollworm numbers were low. That’s not what we expected,” Brown said.

“It’s always difficult to predict,” Catchot added. “We can make generalizations; we can get a terribly cold winter that kills insects, but spring weather and wild host plants availability may have more impact on pest populations.”

As Smith said earlier, consistently monitoring insect pest populations must be an integral part of cotton management, regardless of the weather.

Source: Ron Smith, Delta Farm Press