Best Ways to Ward Off Worms in Lettuce and Cole Crops

Effective lepidopertan control requires the right soil application techniques, followed by tight spray intervals. 

Fields of tender, young lettuce and broccoli look very appealing, especially to insects. Whitefly, thrips and aphids can definitely impact leafy vegetable and cole crop quality, but lepidopteran species pose the biggest insect threat, especially in fall produce grown in the desert southwest.

Lepidopteran pests, including beet armyworm, cabbage looper, corn earworm and diamondback moth larvae, cause the most damage to lettuce and cole crops in the southwestern United States, says John Palumbo, research entomologist, University of Arizona. “We typically see higher levels of fall lepidopteran pressure in September and October. When evening temperatures remain warm into late October and November, worm activity often continues. That was the case in 2013 and 2014, when growers had to deal with worm pressures well into November.”

While the 2015 fall season brought normal temperatures and pest levels, there’s a real possibility growers could face a warmer fall and extended worm pressures again this year, he notes. “For leafy vegetable crops, the threat from beet armyworm and cabbage looper begins at emergence. The potential for crop damage is greatest in the first few weeks, when feeding can significantly reduce stands.”

Soil-applied control
An effective approach for early season control is a well-executed at plant soil application, says Jeff Pacheco, technical sales agronomist, DuPont Crop Protection. “Soil shank injection at planting, followed by sufficient irrigation, is a very effective application method for DuPont™ Coragen® insect control (Group 28). Injecting it uniformly 1 to 2 inches directly below the seed line, at a rate of 5 fluid ounces per acre if targeting lepidopteran species, and up to 7.5 fluid ounces per acre for leafminer larvae control and whitefly nymph suppression, allows it to be easily taken up by developing seedling roots. As the young plant grows, Coragen® is translocated throughout the plant tissue, providing protection at emergence.”

Young plants are least able to tolerate insect feeding in the first few weeks after emergence, says Palumbo. “Coragen® provides good residual control – for 25 to 30 days – when young plants need it most.” When applied by soil shank injection, Coragen® provides the longest-lasting protection against destructive lepidopterous worm pests, and stops feeding within minutes of exposure, adds Pacheco. “It controls larval stage lepidopterous insect pests, including beet armyworm, cabbage looper, corn earworm and diamondback moth larvae in head and leaf lettuce, broccoli, cauliflower and cabbage.”

“Coragen® also offers plenty of application flexibility and can be applied as an in-furrow spray or surface band at planting, or in transplant water, through drip chemigation or as a foliar spray.

Preharvest challenges
Keeping lettuce and brassica crops pest-free until harvest hasn’t been easy in recent years when corn earworm pressures flared, notes Palumbo. “Corn earworm pressures in 2014 were off the charts, the highest we’d seen in the last 15 years, and there’s no simple explanation for it.”

He speculates that one reason the pest wasn’t as prevalent in 2015 was because PCAs were scouting more frequently and tightened spray intervals. “There’s not much room for error with corn earworm control. Once they lay eggs and larvae bore into heads, the battle is lost.”

He says making sure there is a consistent, effective barrier on fast growing plants is the only way to achieve thorough control of corn earworm. “That’s critical to delivering a bug-free crop at harvest.”

“Coragen® is an important foliar treatment alternative for growers who had been using insecticides containing flubendiamide (Belt and Vetica), which recently lost EPA registration,” says Pacheco. “Coragen® works fast, is effective, provides broad-spectrum lepidopteran and leafminer control, has minimal impact on beneficial species, and fits well into an integrated pest management program.”

To prevent insecticide resistance, it’s important to avoid making consecutive applications of insecticides with the same mode of action on successive generations of the same pest, he adds. “No resistance issues with lepidopteran pests have developed yet in desert produce, and following good management plans with proper product rotations should help keep it that way.”

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Advantages of Coragen® Soil Application

  • Good root system uptake and redistribution in hard-to-reach plant parts
  • Extended residual control when Coragen® is within the plant
  • Reduced need for foliar sprays within the first 25 to 30 days
  • Reduced potential for loss of activity from rain, sprinkler washoff or photo degradation
  • Minimal risk to pollinators and other beneficial insects

Always read and follow all label directions and precautions for use. DuPont™ Coragen® is not registered in all states. Contact your DuPont representative for details and availability in your state. Unless indicated, trademarks with ®, ™ or SM are trademarks of DuPont or affiliates. © 2017 DuPont.

Belt® (Bayer); Vetica® (Nichino).