Yellow nutsedge test plots

One of the most significant issues facing vegetable crop growers in the Valley is a weed known as yellow nutsedge. Yellow nutsedge is a very prolific weed that easily outcompetes onions and carrots and can reduce yields beyond 70%. There are currently no herbicides resgistered in onions or carrots for its control. A trial was conducted to test the effects of four herbicides; Outlook, Dual Magnum, Basagran, and Shark, at different stages of onions growth to control yellow nutsedge. The best treatment was Outlook applied at the two-leaf onion stage. This treatment provided atleast 80% control of yellow nutsedge four to six weeks from the application time. The treatment did not appear to have any effect on the onion growth, however yield still needs to be measured. Note: Outlook is not registered for use on onions in California.

Goal 2XL has traditionally been a major onion herbicide. The active ingredient of Goal 2XL is oxfluorfen and is currently only available in an emulsifiable concentrate form, which causes significant injury to onions if applied before the two leaf stage. However, a new formulation of oxyfluorfen, called Goal 4F, appears to cause less injury to the onions and can be applied at the first true leaf at low rates while the weeds are small and easier to control. The chemical showed good results in the first year of trials (2004) in Lancaster and elsewhere in California. Trials in Lancaster showed good control of weeds with low onion injury at the four and six ounce rates applied at the first true onion leaf stage. Note: Goal 4F is not registered for use on onions in California.

Thrips Trial

Thrips are a severe insect pest in onions in the high desert. Over the past few years it has been postulated that these insects have become tolerant to some of the pyrethroid insecticides used as a standard treatment for their control. A trial was conducted in Lancaster to screen new insecticides for their efficacy on western flower thrips. Success (active ingredient spinosad) and Assail (a.i. acetamiprid) showed promising results in controlling thrips up to ten days after treatment. Note that neither of these chemicals are registered for onion thrips and were used for research purposes only, these are not recommendations for their use. These chemicals may be screened again in the future for their efficacy on onion thrips.

Note: This is a brief summary of research results. The results herein are not recommendations for use of these chemicals on these crops. The chemicals mentioned in this summary are currently not registered for use on onions in California.