This weekend I went to my first book signing. It was for Bob Gough and Cheryl-Moore Goughs Guide to Rocky Mountain Vegetable Gardening at Ace Hardware here in Great Falls. Bob and Cheryl are Montana gardening icons who served at the Montana State Extension for decades, and wrote most of the gardening publications used by the county offices. It was a treat to meet Cheryl and have her sign the book.

What was even more of a delight was meeting several other gardening experts in the region. We formed a think-tank of sorts trying to figure out the mystery of a pest that causes potato tunnels. Becky Parker, who has greenhouses with her husband south of Great Falls, works for Ace Hardware and grows their bedding plants and vegetables for the stores. At a recent Home and Garden Show a man from Havre asked her what is drilling into his potatoes.

Potato tunnel mystery

He said its a tiny larvae or worm of some sort leaving exceptionally small tunnels in the potatoes. My friend, Chris, has the same situation. Shes an incredible gardener, but has been battling this infestation for years. She said she loses five to ten percent of her potatoes, and the tunneled areas taste bitter. Chris said shell cut up her potatoes, and allow them to set on the counter because the damage will become visible with oxidation.

So the group of us, including another woman from the Department of Agriculture, stood around Cheryl at her signing table brainstorming what the culprit might be. The obvious choice, potato beetles, didnt fly because the larvae are too large. Same with the tuber worm. The damage is very obvious when theyre in the picture.

One distinct possibility is the flea beetle. Cheryl thought the larvae might be responsible for the damage below the soil level. If this is the case, the most effective course of action is probably discarding the potato seed stock (both Chris and the gentleman in Havre save theirs from season to season), and at worst case treating the potato plants with Sevin (Carbaryl).

Tuber Flea Beetles

I contacted Dr. Nina Zidack, Director of the Montana Seed Potato Certification Program, to see what she thought from our description. She thinks its the tuber flea beetle (Epitrix tuberis). From the photos she sent me, Im sure she nailed it.

Tuber flea beetles overwinter as adults in the soil, which is why its important to rotate the areas where you plant potatoes. Keep in mind, the tuber flea beetles can infect plants up to five meters from where they overwinter so make sure to give them plenty of space from the prior year. There can be 2 to 3 generations with populations exploding two hundred fold per generation – throughout the summer with the final batch doing the most damage to the potato tubers.

Adults are dark colored and 2mm long, while the larvae can be up to 5 mm long and are more off white with a brown head. You might notice a shotgun hole appearance in the leaves with a tuber flea beetle infestation.

To control them with chemicals Sevin seems to be the insecticide of choice; its the one with the least amount of residue on the plants.

If youre not game on using the hard stuff there are several other solutions you can try. Covering the potatoes with a floating row cover when the flea beetle populations are at their peak after May might help keep them down. You can also plant trap crops such as such as Daikon radish or mustard. On the botanical pesticide front, rotenone or pyrethrins are shown to make a dent in the beetle population.

This tuber flea beetle mystery has made quite the buzz in our local gardening circles, but its certainly been a fun exercise to unravel the puzzle.