This year, however, traps in what Rondon describes as the hot area were averaging fewer than one moth per trap per week.
Cultural and chemical controls
Since 2003, Washington and Oregon university researchers have conducted field and laboratory research looking at the pest’s biology and control measures. They say that although they plan to continue trials examining chemical and cultural controls this summer, the past two years of field trials have yielded some encouraging trends.
"A combination of chemicals and irrigation seems to have an effect on tuber moth,” Rondon says. “The drier it is, the more likely there are to be cracks in the soil where tuber moths can find tubers.”
During 2005 field trials, Rondon and her colleagues applied 0.1 inch of water daily between vine kill and harvest—just enough to keep the soil moist.
"It’s very critical right before harvest because after the vines die, the tuber moth seems to prefer the tubers rather than the foliage,” Rondon says. She and her group plan to repeat the trials this season.
Ensuring the tubers are covered with at least 2 inches of soil is another strategy to minimize tuber moth egg laying, says Mark Pavek, a Washington State University Extension potato specialist in Pullman.
"What we have found is that tuber moth typically will infest tubers that are within 2 inches or less of the soil surface,” Pavek says. “The thinking is, if you manage to reduce green tubers, you are managing to reduce tuber moth damage.”
Growers can try to plant deeper, use broader hills or use a combination of the two methods, he says. Depending on the variety, deeper seed placement may be a challenge, since some varieties have difficulty germinating under too much soil.
Schreiber also recommends eliminating cull piles, since the worms thrive on potatoes. Some growers feed culls to cattle, but Schreiber warns the practice won’t eliminate the pest threat unless the animals consume the potatoes immediately.
In addition, he says growers should be vigilant about eliminating volunteer potatoes, since they can harbor the pest.
Several registered treatments
Researchers still don’t know the population threshold that should trigger pesticide application, Schreiber says. The current recommendation calls for treating a field when traps start collecting tuber moths.
Trials conducted last summer show that several registered products are effective against tuber moth. But Schreiber says growers should carefully choose insecticides, because some, such as pyrethroids, may flare other pests, such as aphids and mites.
Schreiber plans to conduct additional trials this summer to study, looking at the best time to treat before harvest. He currently recommends treating no later than four weeks before desiccation, should tuber moth be detected.