UNIVERSITY of CALIFORNIA

Agriculture & Natural Resources

COOPERATIVE EXTENSION •FRESNO COUNTY

1720 South Maple Avenue • Fresno, CA 93702

Tel. (559) 456-7285 Fax (559) 456- 7575

June 5, 2012

To: California Department of Pesticide Regulation

From: Kurt Hembree; Weed Management Farm Advisor, UC Cooperative Extension, Fresno County

Re: Proposed amendments to CCR pertaining to VOC in the San Joaquin Valley Ozone Nonattainment Area

As a weed management farm advisor for the University of California Cooperative Extension, I dedicate about 40 percent

of my research and education activities towards weed management efforts in orchard and vineyard systems in Fresno

County. While my title reflects a responsibility to the people of Fresno County, I am often asked to participate in research

and extension activities throughout the southern San Joaquin Valley, I offer the following comments, concerns, and

recommendations regarding the proposed prohibition on “high VOC” formulations of the herbicide with the active

ingredient oxyfluorfen.

Background on oxyfluorfen use:

Oxyfluorfen is a widely-used herbicide active ingredient throughout orchard and vineyard systems in California. In most

cases, only glyphosate surpasses its use in total acres treated in perennial tree and vine crops in the southern San Joaquin

Valley. Oxyfluorfen plays a particularly important role in controlling weeds during final land preparation to facilitate

harvest operations in tree nut orchards, including almonds and walnuts. This herbicide is used primarily to control a

variety of annual broadleaf weeds, but also controls or suppresses some important grassy species as well. A major benefit

of oxyfluorfen is its ability to provide both preemergent (PRE) and postemergent (POST) weed control.

As a PRE herbicide treatment, it is most commonly applied following harvest in late-fall through late-winter at a rate of

0.5 to 1.5 lb a.i./acre while trees and vines are dormant. Here, the herbicide is applied as a strip treatment within the

planted rows (about 20-40% of the area is actually treated), and rainfall is used to incorporate and activate the herbicide.

During this period, the middles are either mowed, disked, or treated with glyphosate to keep weeds down. As a POST

herbicide treatment, oxyfluorfen is commonly used at lower rates (0.125 to 0.5 lb a.i./acre) in combination with

glyphosate during the growing season within the planted rows. The oxyfluorfen is added to pickup weeds glyphosate

commonly misses, like glyphosate-resistant horseweed, malva, and filaree. To facilitate harvesting almonds and walnuts

off the ground, growers commonly use a mixture of glyphosate (1 to 2 lb a.i./acre) plus a low dose of oxyfluoefen (0.0625

to 0.125 lb a.i./acre) to control weeds across the entire orchard floor.

Most weed scientists would agree that there is little difference in the efficacy between low and high VOC formulations of

oxyfluorfen as it relates to PRE weed control efficacy. However, the low VOC formulation of oxyfluorfen appears to

provide substantially less weed control compared to that of the high VOC formulation of oxyfluorfen. Previously. I

worked with the low VOC formulation of oxyfluorfen in 1st-leaf onions, and found that it was safer on the onions than its

high voc counterpart, but only suppressed small weeds. In those studies, it took nearly twice as much (lb a.i. for lb a.i.) of

the low VOC formulation to provide similar weed control to that of the high VOC formulation. 

Potential impact on the tree nut industry:

The tree nut industry in the southern San Joaquin Valley will be negatively impacted by the prohibited use of the high

VOC oxyfluorfen formulation between the months of May thru October. More than 100,000 acres of almonds, pistachios,

and walnuts are treated monthly during this period with the high VOC formulation of oxyfluorfen (2010 CDPR PUR–

summarized data). Higher costs and perceived reduced control associated with the low VOC formulation, will force

growers to look toward other herbicides that may more costly and/or less effective. Similar effects will be felt by growers
raising other perennial crops like stone fruits, pomegranates, and raisin grapes. 

Alternative measures that were previously proposed:

While the University of California report titled “Proposed Exemptions in San Joaquin Valley Ozone Nonattainment Area

Use Reductions”, which was used as part of the justification for the proposed regulation, considered economics in

considering alternative herbicide options, I am not aware of any summarized data in California looking at the efficacy of

low VOC oxyfluorfen in combination with other POST herbicides outlined in the report. Since these alternative

treatments have not as yet been tested under field conditions in combination with the low VOC formulation of

oxyfluorfen, the report should not be used to help support this legislation. I’m in agreement that the low VOC

formulation could be used in lee of the high VOC formulation during the dormant period as a PRE treatment, but feel

strongly that additional work needs to be conducted to determine the efficacy of the POST combination alternatives.

While I strongly agree with the goals of lowering pesticide VOCs in nonattainment areas, I would caution that equally

important is the need to base new regulation, such as that being proposed, on sound scientific merit. 

Proposed measures:

To help mitigate the issue of VOC emissions from oxyfluorfen in the San Joaquin Valley, I would propose to consider an

additional exemption to section 6884 section (b) to allow the use of the high VOC oxyfluorfen formulation in orchards

and vineyards between May thru October, but only if used at rates of 0.0625 to 0.125 lb a.i./acre. This use pattern is

consistent with the supplemental label for Goal 2XL in almond that allows up to 0.125 lb ai/A as a tankmix partner in

orchard middles and tree rows. This will not only help reduce the total lb a.i./acre of oxyfluorfen used, and it’s

contribution to VOC emissions, but help growers in their efforts to effectively manage weeds in-season in orchards and

vineyard, particularly when preparing fields for harvest. Implementing this exemption would also give researchers much

needed time to explore alternative combinations, including “kickers”, as described in the university report previously

submitted.

I believe restricting and/or prohibiting the use of oxyflurfen EC in the San Joaquin Valley between May and October as

proposed by CDPR, would negatively impact grower efforts to manage weeds in-season in orchards and vineyards,

particularly in nut crop orchards. I respectfully encourage you to consider amending the pending VOC emission

legislation, to allow for the use of oxyfluorfen EC at low rates as proposed in orchards and vineyards in the southern San

Joaquin Valley. Please feel free to contact me if you have any questions or require further information.

Thank you for considering my comments.

Sincerely,

Kurt Hembree

Kurt J. Hembree

Weed Management Farm Advisor

UC Cooperative Extension Fresno County

1720 S. Maple Ave.

Fresno, CA 93702

Office: 559-600-7229

Email: kjhembree@ucdavis.edu

Website: cefresno.ucdavis.edu