Some potato growers on the Eastern Shore of Virginia are wondering about whether or not to spray insecticides for European corn borer, a pest which damages potatoes by boring into stems and causing the whole stem to wilt and die. The practice of spraying for this pest in potatoes has a long history on the Eastern Shore. Growers have traditionally sprayed products like Penncap-M, Furadan, pyrethroids (Asana, Baythroid, or Warrior), or SpinTor for this insect pest. However, there are very few other regions in the U.S., where potato growers spray insecticides for corn borer, including our neighboring state, North Carolina (according to my colleagues).
I am making a strong suggestion to growers that it is time to stop this traditional insecticide spraying in May for this pest on potatoes. Here are my reasons:
1. Many potato growers are using the systemic insecticide Regent at-planting for wireworm control. This insecticide is very efficacious to corn borer larvae. Our research has shown that you will have almost no corn borer tunnels in potato plants treated with Regent in-furrow.
2. There is very convincing evidence from historical moth catch data at blacklight traps that European corn borer densities regionwide have dropped tremendously over the past decade (click on More to see data graphs of historic European corn borer pest pressure in Painter Virginia on different crops). The adoption of Bt corn on the Delmarva is likely a major contributor to this decline in ECB populations. Bt corn provides virtually 100% kill to ECB. Any eggs deposited on corn (the preferred host) will essentially be a deadend for the population. This has been demonstrated in the Corn Belt states as well.
3. There is strong research evidence that potato plants can tolerate a lot of ECB tunneling before economic yield loss occurs. The potato plants may look bad in an infested field, but the damage often comes late when plants are ready to dry down any way.
4. This year, we’ve not caught any ECB moths in our blacklight trap at Painter.
So, I realize that many growers are probably spraying fungicides for late blight on potatoes currently. You’re probably convinced that adding an insecticide in the tank makes economical sense. But, if you don’t need it, then it really doesn’t make sense. The only other damaging insect pests of potatoes on the Eastern Shore are Colorado potato beetle and potato leafhopper. Both of these insects should be controlled by the at-planting applications of a neonicotinoid such as Admire, Platinum, Venom, Tops MZ-Gaucho, or Cruiser.

Sincerely,
Tom Kuhar
Associate Professor of Entomology
Virginia Tech
Additional information: ecb-infestation-over-time-graphs-docx