California Pepper Commission


Proposal Smith Preemergence Weed Control

California Pepper Commission - Research Proposal, 2013

Title: Preemergence Weed Control Trials in Peppers

Principle Investigators:
Richard Smith
Farm Advisor, Monterey County 1432 Abbott Street
Salinas, CA 93901
(831) 759-7350; (831) 758-3018 FAX

Timeline: March 1, 2013 to February 28, 2014


Peppers are long-season vegetables that have a several effective registered herbicides; however, there are gaps that remain in the spectrum of key weeds controlled by currently registered herbicides (Smith et al., 2008). As a result, growers may spend significant amounts of money, especially later in the season, to control weeds in peppers. Peppers have a good array of weed control materials available to enable growers to be able to control many problematic weeds. However, given the long growth cycle for peppers, late season weed control continues to be a problem on pepper grown without plastic mulch. Our efforts over the past few years have been to evaluate herbicides and combinations of herbicides to provide late-season weed control.

In 2012 we observed that Zeus (FMC Corporation) showed promise as both a pretransplant and layby herbicide for use in peppers. This material has potential for at least partially controlling malva and we would like to evaluate rates to effectively control this weed. It also has some preemergent activity on yellow nutsedge.

Layby Herbicide: Effective layby herbicides would provide effective weed control later in the season and reduce late-season weeding costs. Dacthal, Prowl H2O and Dual Magnum are registered for use at layby in pepper production. Prowl H2O provides excellent control of many broadleaf weeds such as lambsquarter, nettleleaf goosefoot and mustard. Dual Magnum controls a similar weed spectrum to Prowl H2O, but is also effective against hairy and black nightshade, and yellow nutsedge. None of the currently registered layby herbicides are effective against malva (Malva parviflora) or field bindweed.

Other materials that warrant further evaluation for use on peppers include:

Table 1. Proposed weed control treatments
No. Pre-transplant ApplicationLbs a.i./A
2Dual Magnum (standard) pretransplant 1.43
3Zeus 4F pretransplant 0.094
4Zeus 4F pretransplant 0.188
5Outlook 6.0 pretransplant 0.60
 Layby Application  
6Untreated ------
7Dual Magnum 7.62 +
Prowl H2O 3.8EC (standard)
8Outlook 6.0 Directed0.60
9Zeus 4F Directed0.094
10Zeus 4F Directed0.188


  1. Examine layby weed control strategies for early and late season weed control.


Weed control trials will be established in Monterey County. Pretransplant applications will be made before transplanting and layby applications will be made approximately 30 days following planting. Crop safety, weed control, yield and quality evaluations of the peppers will be conducted.

Literature Cited

California Pesticide Impact Assessment Program (CPIAP). 2000. Crop Profile for Bell Peppers.

Smith, R. F, O. Daugovish, C. Bell and T. Lanini. 2008. Pepper Pest Management Guidelines - Weeds.
University of California Integrated Pest Management Program. Available on line at:


I. Budget

A. Salaries
Field Assistant $3,500

B. (30% time, 4 months)
Travel $1,500

C. (200 miles/week for 14 weeks @ $0.51/mile)
Monterey County $5,000

D. Total $5,000


Richard Smith
Richard Smith
Principal Investigator

Maria De La Fuente Monterey
County Director

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