Carrot Country

UC Researchers Look at Weed Control in Carrots

Carrot Country
Winter 2006

Currently Lorox and Trefl an are standard herbicides used for weed control in carrots. It has been well known for some time that carrots were relatively tolerant to Prowl 3.3EC, however it was never registered for use. With the advent of new formulations of pre-emergent herbicides, and greater weed problems like yellow nutsedge, there is a need to evaluate new herbicides for use in carrots.

Several pre-emergent materials were applied in two different trials in 2005. During 2004 Outlook was applied to carrots in the third to fourth true leaf and they appeared to be relatively tolerant to the material at that growth stage.

Prowl H2O, a new water-based formulation of Prowl 3.3EC, was released in 2005 which had not been researched on carrots. Prowl H2O and Outlook were evaluated
for weed control and carrot tolerance when applied at different rates shortly after planting.

In another trial conducted later in the year, Outlook was applied again at planting and completely killed the carrot stand. Outlook appears to be too damaging to carrots if
applied before the third true leaf. Although the Outlook treatment shortened carrot size in the trial (data not shown), it may have been misleading to include the data after the second trial where Outlook completely killed the carrot stand.

All of these treatments were applied after planting but before carrot emergence. Weed control was the greatest in the Lorox and Prowl H2O (32 oz/acre) treatments.
The one pint (16 oz/acre) rate of Prowl provided no weed control. Although none of the treatments decreased the overall carrot yield, the Outlook treatments did show a higher percentage of carrots in the smallest size class (data not shown). Outlook and Prowl H2O appeared to be a little weaker on puncturevine than the Lorox treatment in this trial. In another carrot herbicide trial with 15 herbicide treatments, Nortron provided adequate control of yellow nutsedge with minimal carrot damage. Nortron will be evaluated in trials in 2006 for its effi cacy on yellow nutsedge and carrot tolerance at different carrot growth stages.

Editor’s note: The material here is reprinted, with permission, from the University of California Cooperative Extension’s High Desert Ag Notes, Volume 4, Issue 1, spring 2006 issue. For more information, contact: Grant Poole, U.C. farm advisor, Los Angeles and San Bernardino counties, gjpoole@ucdavis.edu.