Klamath onion production is a constant challenge

When it comes to growing onions, the Klamath Basin has unique challenges.

"This year, we've had some hailstorms and thunderstorms that have come through that caused quite a bit of damage, and the weeds seem to recover much better than the crops," said Rob Wilson, center director and farm advisor for the University of California Intermountain Research and Extension Center in Tulelake.

Wilson has been conducting research on onions, and he currently has three research projects going on—weed control, seed corn and onion maggot control, and white rot.

Wilson is looking at a variety of different ways to control white rot with fungicides. He's also trying to reduce the white rot sclerotia, which are the reproductive part of the disease in the field by applying a variety of germination stimulants.

Seed corn maggot and onion maggot are species that are a problem in Klamath Basin onions, Wilson said. The maggots will feed on the seedling onions and reduce the onion plant population in the field.

"We've seen a big increase in the number of maggot flies in the field, and I don't know if that's due to the increased alfalfa acreage that we have, or just guys planting onions in fields that didn't have a real stale seed bed," Wilson said.

"Anytime you have decaying organic matter—whether that's weeds or alfalfa or other things—that really is a good attractant for those maggot flies to lay their eggs. And then the maggots hatch in the soil, and they just feed on the onion seed or the developing seedling," Wilson said.

"It's a big devastation because their feeding actually kills the onion, and if you reduce plant population enough, you just never can recoup," he said.

There are few insecticide options for controlling the maggots, and Wilson said he is looking for alternative insecticides that growers can apply in furrow or on treated seeds.

"The most standard insecticide that's been used for a lot of years is chlorpyrifos or Lorsban," Wilson said, but he said growers aren't getting the same level of control that they used to get.

"In other parts of the United States, there's a lot of documented resistance to chlorpyrifos with maggot species. We can't say that now. We're still getting some activity, but there does seem to be either a higher number of maggots that the treatment isn't able to control anymore, or the maggots are developing a little more tolerance to the insecticide," Wilson said.

Right now growers can still get activity out of Lorsban, Wilson said: "It's still one of the better treatments, but it's not providing a level of control that the grower can say, 'This is acceptable.'"

Lorsban is also one of those insecticides that has some environmental concerns, and there has been recent talk of trying to reduce the number of uses of that product, Wilson said.

"We're hoping to be proactive and find alternatives to use, so that we have one different mode of action," he said, adding that this will allow growers to rotate insecticides, hopefully avoid building resistance, and if Lorsban is restricted, growers would have alternatives.

Wilson's third project is weed control, and he has tested several new herbicides for use in onions.

It seems like growers are being forced to leave a lot of historically premium ground for onions because it has become infested with white rot, Wilson said. This means growers are having to lease and grow onions in other areas where they typically haven't grown onions in the past, he added.

Growers raising onions on the Walking Wetlands have restrictions on several herbicides, Wilson said.

"Over time, the weed populations have increased pretty significantly in those fields," he said.

Scott Seus, an onion grower in Tulelake, said weed control is a major issue in growing onions.

"I think we're getting better at it all the time," Seus said.

He attributed that to Wilson's research and how he's shown growers how to use different materials like pre-emergents and time their applications better.

Finding new chemistries is important, and Wilson's research is doing that, plus he's getting the supporting documentation so that new products can receive registration for use by growers, Seus said.

Coming up with the documentation to take to the California Department of Pesticide Regulation to support the registration of new chemistries is important work Wilson is doing, Seus said.

Pre-emergent applications have also helped hold back some of the problem weeds, Seus said.

The major weeds Wilson is working on are lamb's quarter, kochia and redroot pigweed. While they aren't herbicide resistant, they are difficult weeds to control, he said.

Seus said he also struggles with nightshade, shepherd's purse and mustard.

"Those tend to be the ones that give us the biggest fits," Seus said.

Unlike other crops, onions aren't very competitive with weeds, Wilson said.

"Really for the full season, there's a lot of light that is able to make it through the canopy," Wilson said, whereas a potato field has a much quicker establishment phase.

"Onions take anywhere from 14 to 21 days to actually emerge out of the ground from seeding, and then another good month before they're any bit competitive. And we have to irrigate them frequently because they are a shallow-seeded, small-seeded crop that we have to keep the soil moist," Wilson said.

Seus agreed getting the onions tall enough to outcompete the weeds is a challenge.

"It's actually the middle of July that we have plants that are competing against the weeds and shading things out," Seus said.

Seus said Wilson's work and the support of the California Garlic and Onion Research Advisory Board has been very important to the growers in the Klamath Basin.

(Kathy Coatney is a reporter in Bend, Ore. She may be contacted at kacoatney@gmail.com.)