Pest lives in cull piles, can destroy 90 percent of a crop
By SEAN ELLIS
An Idaho program that prohibits cull onion piles in the spring is credited with helping to stop the spread of the potentially devastating onion maggot.
But with another wetter-than-normal spring in parts of southwest Idaho, Idaho State Department of Agriculture officials are reminding growers that no cull onions are allowed at packing sheds, infields or animal feed facilities in Ada, Canyon, Gem, Payette, Owyhee or Washington counties.
On consecutive years of wet springs, the insect has been known to destroy 80 to 90 percent of the crop, Mike Cooper, agricultural bureau chief for the ISDA's plant industries division, said.
The onion maggot "is probably one of (onion growers') biggest early season insect problems," he says. "If we keep all the culls cleaned up, that's one less reservoir for these things to live in and attack production fields."
Onions sorted this time of year must be properly disposed of within one week and trucks transporting the crop must be covered to prevent spillage along roadsides.
Proper disposal options, which include pit burial, feeding, composting, spreading, chopping and shredding, are detailed in the ISDA publication, "Cull Onion Disposal in Idaho."
In its larval stage, the onion maggot attacks and destroys portions of the onion bulb, causing bulbs to rot during storage, Cooper said. The maggot is frequently found in cull onion piles. When they emerge in April and May, the maggot adult flies are attracted to the volatile odors given off by sprouting onions and new seedlings.
"They start flying over to the new crop and lay eggs there," said Bob Komoto, manager of Ontario Produce, which packs and ships onions from west Idaho and east Oregon. "Once those eggs hatch, the larvae start destroying the new crop."
Komoto said the onion maggot can be devastating -- each onion maggot can destroy up to two dozen seedlings during its two-week life span -- but the Idaho program, as well as a similar one for east Oregon growers, has all but eradicated the problem.
Onion growers know the danger posed by the pest and have followed the program pretty closely, he said. "Some people are a little slow, but it's pretty well complied with."