What is in this article?:
- North Carolina develops wireworm control program for sweet potatoes
- Larval stage of click beetle
- Damage can be severe
• North Carolina is the country’s largest sweet potato producing state, totaling nearly half the entire production in the U.S.
• Despite annual production of 600 million pounds or so, worth more than $175 million, until recently there was no consistent plan for managing wire worms — the leading insect threat to sweet potato production in the state.
• Now, thanks to a multi-state research program and the recent addition of Mark Abney to the research and Extension program at North Carolina State University, sweet potato growers have a uniform wireworm control program to follow.
Larval stage of click beetle
Wireworms are the subterranean larval stage of click beetles (Coleoptera: Elateridae). Though wireworms feed on corn, sorghum, small grains, tobacco, and various vegetables, they are particularly damaging to potatoes.
These pests can and do feed on seed pieces (on Irish potatoes) early in the season, causing weak, sporadic stands. However, the big damage to both Irish potatoes and sweet potatoes is damage done to maturing tubers and roots that make harvested potatoes less valuable and in many cases unmarketable.
Abney is among a team North Carolina State researchers, who developed a new insect management strategy that saved sweet potato growers an estimated $250 million last year.
The new management strategy also reduces the amount and impact of pesticides released into the environment.
Abney, speaking at the recent North Carolina Vegetable Growers Association annual meeting, says “Prior to 2006, in all the sweet potato growing states in the Southeast, we really didn’t know what the major pests were. We knew we had wireworms, we knew we had several other insect pests, but there was no composite picture as to how many of what insects were in sweet potatoes, nor how much damage these insects were causing.”
Abney was part of the multi-state project that ran from 2004-2007 and was designed to document which insects were major pests of sweet potatoes and begin the process of developing comprehensive IPM programs to best manage these pests.
After three years of taking sweet potatoes from 95 grower fields and analyzing damage in a lab, it was not a surprise that wireworms were our biggest insect problem. More than 20 different growers agreed to leave a portion of these fields untreated; they found 17 percent of the sweet potatoes had wireworm damage. Sweet potato flea beetles were second, causing damage on 11 percent of roots and a combination of white grub, white fringe beetles and other insects made up a smaller percentage of damage.
“This damage was corrected for marketability, so 17 percent of the sweet potatoes we tested over three years were unmarketable due only to wireworm damage. Had we tested just for damage, regardless of whether the sweet potatoes were marketable or not, probably more than 40 percent were damaged,” Abney says.
“So, growers who don’t treat with an insecticide for wireworm control on sweet potatoes should expect 40 percent or more of their crop to be damaged by wireworms and for 17-20 percent of the crop to be unmarketable,” he adds.
“Though we have at least 8 different species of wireworms in sweet potatoes in North Carolina, the tobacco wireworm makes up 85 percent of the wireworm complex. So, if we can manage this one species, we have made good progress in managing wireworms,” Abney says.
However, he adds, corn wireworm, which makes up a relatively small percentage of the total wireworm complex causes tremendous damage — much more so than tobacco wireworms.