Onion growers confirm success of applying herbicide through drip system
ONTARIO, Ore. — Oregon State University field trials have shown that applying the herbicide Outlook through drip irrigation works much better than surface application in controlling the yellow nutsedge weed.
Now grower experience is confirming that research.
Farmers who produce yellow bulb onions in Idaho and Oregon received special permission for the first time this year from their state agriculture departments to apply Outlook through drip irrigation. Previously, they were limited to surface application of the herbicide.
“We were very successful with” applying it through a drip system, Nyssa farmer Bruce Corn said. “It worked very, very good.”
About 95 percent of the 20,000 acres of bulb onions grown in Southwestern Idaho and Eastern Oregon are yellows and about 60 percent of them are on drip irrigation systems.
According to OSU researchers, Outlook is one of the most effective tools in controlling yellow nutsedge, which is the main weed challenge for growers in this region.
OSU Weed Scientist Joel Felix said growers who have used Outlook in drip systems this year are reporting good results.
“The growers that I’ve spoken to so far that are using it in a drip system are quite happy,” he said. “If you have a drip system, I think you’ll be wasting your money applying it over the top ... because we’re seeing much better nutsedge control from applying it through a drip system.”
The field trials Felix has led at OSU’s Malheur County Research Station the past three seasons are occurring in silt loam soil, and he said farmers with lighter soils would likely be better off applying Outlook at lower rates than those being applied at the station.
Growers in the area are limited to applying a total of 21 ounces of Outlook through a drip system per season.
The OSU trials are experimenting with different application rates.
For example, 7 ounces of the herbicide is being applied three different times over three weeks or 11 ounces is being applied and then 10 ounces two weeks later.
The herbicide will be more available in lighter soils than it is in loamy soils because of the reduction in organic matter and farmers with lighter soils should probably apply the herbicide at smaller rates, Felix said.
Applications are being studied at the plant’s two-leaf stage and having more of the herbicide available to the young plants could cause injury to them, Felix said.
“On the lighter soils, it might be better to go 5-5-5-6 or 7-7-7 or you may end up getting more injury to onions than a grower can stomach,” he said.
He said it’s also important that the herbicide be diluted with water and applied over an extended period. For example, OSU researchers are mixing 7 onces in 35 gallons of water and injecting that solution into the drip line for eight hours.