Practical Winery
58-D Paul Drive, San Rafael, CA 94903-2054
phone:415/479-5819 · fax:415/492-9325

May/June 2001

Improving sulfur management

Joe Browde & Cliff Ohmart
California Winegrape Pest Management Alliance

Winegrowers have “dusted off” their sulfur dusters and are into another season of battling powdery mildew. Most growers know that the Department of Pesticide Regulation (DPR) has a watchful eye on dusting sulfur, primarily due to public complaints of drift.

Because of sulfur’s importance for mildew management programs across the state, we will review the issues with drift in sulfur application and suggest best management practices.

Sulfur is a natural element used safely for centuries to control plant pathogens and mites. As an active ingredient, sulfur is the leading pesticide used in California agriculture. It is a very important and effective tool for managing powdery mildew — one of the major diseases affecting winegrapes in California and throughout the world. Uncontrolled mildew seriously reduces both winegrape yields and quality.

Human exposure to sulfur can cause eye irritation, breathing difficulty, and skin irritation — especially in sensitive individuals. But, compared to most other pesticides, it has minimal effects on humans and the environment. In fact, sulfur use is approved for organic farming.

So, what is the concern?
The issue is clear. A number of high profile reports of sulfur drift have occurred over the last few years. Public complaints were the source for most of these reports. Consequently, DPR conducted a survey of all counties during June 1999. Results indicated that 34 drift incident reports involved sulfur in both 1997 and 1998. For 1999, 18 incidents involving sulfur drift already were reported by June.

About two-thirds of the reports cited grapes as the target source (Figure 1), distributed throughout all winegrape regions (Figure 2). Moreover, approximately 80% of reports for grapes were attributed to dust applications (data not shown). Incidents included dust drifting from its intended crop target onto surrounding structures, such as neighboring residences, schools, and places of business. Dust drift onto workers in surrounding fields and moving vehicles was also reported.

Dusting sulfur constitutes the foundation for powdery mildew control in grapes throughout California. In fact, a majority of winegrape acres are treated with dusting sulfur each year — many treated repeatedly.

Why have there been more complaints recently? The key factor seems to be the increase in agricultural/ urban interfaces.

Many urbanites do not fully appreciate agriculture and the need for judicious, tactical intervention for managing pests. Unfortunately, too many regard all pesticides (including sulfur) as bad and equally toxic. Because of its extensive use, visibility, and susceptibility to offsite movement by wind, dusting sulfur must be managed with particular care to prevent drift and complaints.

Collaborative efforts to improve sulfur management

According to the law, applicators must use pesticides in a manner that minimizes the potential for drift to nontarget areas. Due to increasing reports of sulfur drift, DPR put sulfur registrants “on notice” in November 1999. Regulators gave them an opportunity to reduce complaints before imposing specific legal restrictions related to sulfur and its uses.

Sulfur registrants formed the Sulfur Task Force (STF), which developed a supplemental label for dusting sulfur. STF has worked with the Coalition for Urban/Rural Environmental Stewardship (CURES; Parry Klassen, executive director) to develop a sulfur stewardship program. The program includes production of stewardship manuals and implementation of a grower outreach program.

The California Winegrape Pest Management Alliance (PMA) is complementing and expanding the STF/CURES effort through additional education of winegrowers and the general public. PMA is a grower-driven collaboration with DPR to promote reduced-risk pest management.

The California Association of Winegrape Growers (CAWG) provides organizational leadership, and a steering committee comprised of representatives from regional and statewide winegrape organizations, helps guide efforts. Funding is provided by a grant from DPR. Karen Ross, president of CAWG, is the principal investigator.

The PMA strongly advocates educating the public about the low toxicity of sulfur, the rationale for mildew management, and the genuine concern that farmers have for the welfare of their neighbors, employees, and the environment.

But, the farming community must do its part by using best management practices for application of sulfur (and other pesticides) to minimize the potential for drift from treated vineyards, especially to surrounding “sensitive areas.”

PMA is holding field days across the state as venues for grower-to-grower transfer of practical techniques and systems for managing sulfur near sensitive areas.

This education will benefit the winegrape community and the general public, as sulfur management practices are improved, drift incidents are reduced, farmer-community relationships are enhanced, and sulfur and its uses are sustained. The intent is to greatly reduce or eliminate public complaints about sulfur drift.

What are sensitive areas?
Sensitive areas are locations surrounding a vineyard where people, organisms, or structures could be exposed to pesticides. Based on drift incidents with sulfur, these areas include schools, bus stops, busy roadways, residences, or other areas of human activity.

Sulfur sensitive areas also can include nearby crops (such as pears) and waterways. By careful evaluation, it should be easy to identify sulfur-sensitive areas near vineyards. Growers should consider contacting their county agricultural commissioner’s office to help determine specific local areas.

How to reduce the potential for drift and avoid incidents?
Growers are integrating a number of practices into site-specific programs for effectively managing sulfur near sensitive areas. Growers can review the list below and work with applicators to develop a plan incorporating those practices appropriate for their vineyard and circumstances. It is critical that applicators fully understand the plan as it relates to the geography of their vineyards and surrounding areas. Many of these tactics also are described in the CURES publication Sulfur, Best Application Practices.

Best management practices
• Being a good neighbor. Sulfur stewardship includes being aware of the concerns of neighbors, and local communities. Consider a policy of discussing vineyard actions with neighbors, speaking with community organizations about the importance of sulfur as a relatively benign crop protection tool, and forming a regional team of growers to serve as the first contact with the public for negotiations and troubleshooting. These actions promote mutual understanding and better relations, thus decreasing the probability of complaints.

• Canopy management. Use trellis systems and canopy thinning techniques (leaf pulling, shoot thinning, cane cutting) that open canopies to recommended levels. Besides benefitting fruit quality, a properly opened canopy provides conditions less conducive to mildew and other diseases, potentially lowering sulfur rates and reducing applications for achieving adequate coverage.

• Monitoring mildew development. Use the powdery mildew index as a tool for optimally timing and possibly reducing the frequency of fungicide applications (including sulfur).

• Establishing buffers. Establish reasonable buffer zones to prevent drift onto sensitive areas and public exposure to applications. Buffer distances vary with weather conditions, formulation (dust/wettable), application method (ground/air), presence of barriers (e.g., trees), and characteristics of sensitive areas. If buffers determined for dust application overlap some border vine rows, apply separate fungicide sprays (less prone to drift) to these rows or dust border vine rows during conditions when buffers can be reduced.

• Dealing with extra-sensitive areas. Consider applying wettable sulfur or other low-risk fungicide sprays to vineyard portions or entire vineyards near extremely sensitive areas.

• Selecting rates. Adjust application rates of sulfur or other fungicides to the lowest effective rate according to vine growth and development. Higher label rates may not be required early in the season to achieve adequate coverage. Use of lower rates also can decrease risks of pesticide drift, particularly for dusting sulfur.

• Equipment operation. Maintain, calibrate, and select application equipment to ensure accurate delivery of the intended rate. For dust, be extra cautious of drift during row turns, and reduce RPM at row ends or shut off dusting equipment if possible.

• Weather monitoring. Monitor weather conditions before and during applications. No sulfur applications can be made when winds exceed 10 miles per hour, but consider using an even lower threshold. Avoid applications when winds are blowing toward sensitive areas and during temperature inversions.

• Timing applications. Decrease public visibility and the potential for complaints by making applications during periods of least human activity (e.g., at night, weekends). Develop a sequence for application that attracts the least attention. For nighttime applications, minimize “noise” complaints by treating rows closest to residential areas first.

• Resistance management. Although mildew resistance to sulfur has never been found, consider rotations with other fungicides as a preventive measure against resistance and potential sulfur drift.

It is important for winegrowers to be proactive in resolving important environmental and social issues. Addressing the issue of public complaints about sulfur drift is no exception. Growers must develop and apply best management programs for sulfur to prevent further regulation and to retain sulfur as a viable tool for agricultural production.

Joe Browde is Project Coordinator, California Winegrape Pest Management Alliance
Cliff Ohmart is Research/IPM Director, Lodi-Woodbridge Winegrape Commission