& 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 sulfurs 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
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
|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
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
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
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
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
PMA is holding field days across the state as venues for grower-to-grower
transfer of practical techniques and systems for managing sulfur near
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 commissioners 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
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
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
Cliff Ohmart is Research/IPM Director, Lodi-Woodbridge Winegrape Commission