What is in this article?:
- Dual attack on white grubs promising in Carolina sweet potatoes
- Only cotton a non-host
- Paralyze target insect
• Unfortunately, sweet potatoes are not marketed based on their nutritional or medicinal value, instead they are still marketed primarily on how they look.
• White grubs, or plectris grubs, make sweet potatoes look bad, very bad.
SEVERE DAMAGE from plectris grubs can make sweet potatoes, like these, unmarketable.
Only cotton a non-host
Among the major crops grown in the region, only cotton appears to be a non-host for these insects. The biggest economic impact has been felt by sweet potato growers.
These insects are amazing in the way they damage potatoes, Abney says. They feed on the surface, making large, ugly gouges and craters on the sweet potato. In too many cases affected potatoes aren’t even marketable as processing potatoes.
In the processing plant there is no way to stop and cut out the affected part of the potato. Though the potato doesn’t die from the damage, in most cases the gouges and craters on the surface make them unmarketable.
North Carolina is the No. 1 sweet potato growing state in the country and currently produces more than 40 percent of the U.S. crop.
Though it has been found in only a small part of the North Carolina sweet potato growing area, it has created concern across the entire U.S. sweet potato industry.
Abney has been at the forefront of containing white grub damage and has worked in sweet potatoes for most of his professional life.
After looking at numerous insecticide options, he says it looks like a two-pronged attack with insecticides and natural predators of the insect may offer hope in containing and managing plectris grubs.
Abney uses the term ‘entomopathogens’ to describe one biological approach he and his research team has undertaken to stem the movement of these white grubs.
One of his graduate students, Amber Arrington, has been using entomopathogens in combination with the most effective insecticide family used to combat white grubs.
“Using traditional organosphosphate insecticides has proven to be mostly futile in managing white grubs,” she says.
“By switching to neonicotinoids, a relatively new family of insecticides, control was better, but we were still seeing 50 percent damage in some fields,” she adds.
Control of plectris grubs with neonicotinoids continues to show promise, but damage is too high to prevent economic losses in sweet potatoes.
Previous research demonstrated some synergistic activity between neonicotinoids and pathogenic fungi and nematodes when used in combination to kill white grubs.