Herbicides tested in the seven-year trials included: S-metolachlor (Dual Magnum); flumioxazin (Chateau); oxyfluorfen (Goal Tender); dimethenamid (Outlook); pendimethalin (Prowl H20); and napropamide (Devrinol) and Dacthal.

Among the findings, Le Strange reports that Dual Magnum and Goal Tender effectively control the nightshades. Goal Tender is very effective on puncturevine while other products including Dacthal, Devrinol, Dual Magnum, and Prowl H2O provide partial control. Dual Magnum is effective against yellow nutsedge, but not purple nutsedge. Most of the herbicides work against common purslane and the pigweeds.

For little mallow, no registered herbicides are currently registered for layby use. Goal Tender works against the weed but is not registered. Chateau works, but can cause crop phytotoxicity (stunting).

Dual Magnum was successfully utilized in commercial bell pepper production at planting from 2002 to 2007 due to a special 24c exemption permit gained by the California Pepper Commission.

The herbicide provided good weed control in the field trials. Le Strange and Smith worked with the manufacturer Syngenta in 2008 to gain an indemnified label for product use at layby. To gain label use, growers must visit Syngenta’s website http://farmassist.com.

“Dual Magnum at planting and layby provides very good weed control,” Le Strange said.

Chateau is not currently registered in bell peppers yet provided excellent weed control in the trials. Herbicide use can result in crop phytotoxicity. Le Strange is working with Valent to determine the best formulation (spray versus granule), timing, and application rate. Chateau is primarily used for weed control in orchard crops.

Goal Tender is registered for use in peppers grown with plastic mulch and is applied to shaped beds before planting. Le Strange says Goal Tender also works effectively without mulch. Leaf crinkling, necrotic spotting, and leaf death can occur if applied less than 30 days before transplanting.

Outlook currently lacks registration in peppers but provided excellent weed control in the trials. Work is underway with BASF to determine the best application method, timing, and application rate. Crop phytotoxicity with Outlook occurred once in the trials but was never replicated.

Prowl H2O is registered for planting and layby applications. The herbicide controls many broadleaf weeds including lambsquarters, goosefoot, and mustards. Prowl H2O is not effective against the nightshades or yellow nutsedge.

“We see very good weed results using Prowl H2O especially on grasses in the field,” Le Strange said.

The pepper herbicide research trials will continue in 2011.

“When we started the trials there were very few herbicides registered for use in peppers,” Le Strange said. “We have a few more now as a result of our research. This is good progress in the effort to control weeds and costs in the California pepper industry.”