Tuber moth found in Klamath Basin

By HOLLY OWENS
Freelance Writer

Capital Press - January 20, 2006

KLAMATH FALLS, Ore. – The potato tuber moth, an ancient pest that turned up in the Columbia Basin in 2002, has now been confirmed in the Klamath Basin, shared by Oregon and California.

Helmuth Rogg, an entomologist with the Oregon Department of Agriculture, reported the find at the Jan. 12 Intermountain Pest Management seminar.

Rogg said most of Oregon’s 2005 finds were recorded last January, apparently when mature moths flew out of storage sheds during a warm spell.

Discovery of tuber moths in stored spuds is cause for rejecting shipments, with most inspection agencies having a zero tolerance for the pest.

Phil Hamm, a plant pathologist from Oregon State University’s Hermiston Agriculture Research and Extension Center, said another flight emerged in March, indicating a different cycle than the insect showed in 2004.

Hamm said he believes the Columbia Basin moth population to be a unique variety, different from other strains of the pest.

Tuber moths are a versatile pest and are found around potato crops worldwide. They can also be seen on related host crops such as tomatoes, eggplant and tobacco as well as on related weed crops such as buffalo bur and nightshade.

Tuber moths were first reported in the Pacific Northwest in 1912 in the Yakima, Auburn and Seattle areas, Hamm said. Boise first reported the pest in 1959, and Oregon in 1972. The pest has been a fact of life in California’s Bakersfield spud production area for decades.

Hamm said researchers didn’t find tuber moths until they went looking for them – and they’re not easy to find or positively identify.

Rogg and Hamm advised growers to bring in potatoes or moths to local extension offices for identification.

The moths – and the larvae – are only a quarter-inch in length, with two to three dark spots on the wings and look similar to a wide variety of moths. The moth’s eggs, which can be laid on foliage, in the ground or on tubers are a mere 4/100-inch long.

“If you go looking for these in the soil, you’ll be looking a long time,” Hamm said.

Entomologists use pheromone-baited traps to catch tuber moths. There were 53 tuber moth traps located throughout Oregon in 2005.

The moths are nectar feeders, most active at dawn and dusk.

They travel from field to field by flying short distances near the ground. Females prefer to lay eggs on the underside of leaves if foliage is available, but will also reach tubers through cracks in the soil and lay eggs in the eyes of potatoes. A female can lay from 60 to 200 eggs in her lifetime.

Depending on the temperature it can take 2 1/2 to 11 weeks for a tuber moth to go from egg to adult. The moths are originally from South America, Rogg said, and thrive in warmer temperatures. A warmer climate can see up to 10 to 12 generations per year.

With the Northwest’s colder climate, Hamm said, moths aren’t completing an entire life cycle in one season. At a stable 50 degrees, it takes 5.3 months for one generation to complete a life cycle, and at temperatures below 50 degrees their development threshold is lowered.

“We don’t find them wearing long underwear,” Hamm said.

Above ground, tuber moth larvae burrow in to the stems of the plants, damaging the cavities in the stem. A grower would have to be looking for the damage and know what kind of damage to know if the plants were infested.

“It doesn’t cause that much damage,” Hamm said.

What does cause damage is when larvae burrow into the tubers, leaving dirty tunnels, unlike wire worms which dig clean tunnels, which then heal.

“Tuber moths have dirty holes, and they’re never healed,” Hamm said.

The tunnels open the door for secondary infections and fungus, Rogg said, and they also make the potato unusable.

When scouting around for damage, Hamm advised growers to sample nine plants along the perimeter of a field where the prevailing winds occur. If there is any tuber moth damage, it most likely will be found in the upper canopy of the plant.

Pheromone traps, although useful to detect the presence of tuber moth, are not a reliable measure of what kind of damage there may be to the crop.

There are cultural, chemical and biological options for controlling tuber moth.

They thrive in warm, dry weather in summer, and mild winters. They can be deterred from reaching tubers by keeping the soil moist and eliminating cracked soil by using overhead irrigation and rolling the soil, Hamm said.

Colder temperatures in potato cellars will keep the pests inactive.

Spraying with insecticides, such as pyrethroids, organosulphates and carbomates three days before harvest, a practice used in California, along with rolling the soil, is also effective.

“For the most part, most things work for adults,” Hamm said.

But Hamm also advised growers to not exclusively use the lesser-expensive pyrethroids. The tuber moth may eventually build up a resistance to the pesticide. “It’s extremely important not to use pyrethroids all the time.”

And also before harvest, recent trials weighing the effectiveness of natural die-off of vines vs. chemical die-off favor chemical die-off to reduce crop damage.

In South America, Rogg said, parasites and disease are used to fight the tuber moth. There is no program yet in the U.S. to distribute a parasitoid agent because it is classified as an exotic pest. Scientists are evaluating the parasite to see if it’s safe to introduce here.