By: Dr. Jonathan E. Oliver (Fruit Pathologist and Extension Specialist, University of Georgia – Tifton Campus) and Dr. Peter Oudemans (Director of the Philip E. Marucci Center for Blueberry & Cranberry Research in Chatsworth New Jersey and Professor, Department of Plant Biology, Rutgers University)
Fungicides containing captan remain an important component of blueberry spray programs for disease control. Both solo and tank-mix applications play a valuable role in resistance management because captan has a multisite mode of action, making the development of fungicide-resistant pathogen populations unlikely. When used according to label instructions, captan provides broad-spectrum disease control and a low risk of resistance, making it a valuable tool in integrated spray programs.
However, improper use, particularly incompatible tank mixes or unfavorable application conditions, can result in phytotoxicity (plant injury). Growers should therefore understand both the benefits and the risks associated with captan use.
Captan is a broad-spectrum biocide that is toxic to any cell it enters. Its selectivity depends largely on differential uptake: fungal cells readily absorb captan, while plant cells typically do not. When applied properly, captan does not readily penetrate plant tissues. Certain additives, especially those that promote cuticle penetration can increase absorption into plant cells and lead to injury.
For this reason, captan labels warn against combining the product with oil-based sprays or applying it immediately before or after oil applications. Similarly, strongly alkaline materials (high pH), such as spray lime, lime-sulfur, or Bordeaux mixture, should not be tank-mixed with captan. Tank mixing captan with emulsifiable concentrate (EC) formulations is also not recommended and may increase the risk of phytotoxicity.
Careful attention to label directions, tank-mix compatibility, and spray timing will help growers capture the benefits of captan while minimizing the risk of crop injury.
Need for Captan Where Resistance Limits Options
Because plant injury can occur under certain conditions, growers often seek alternatives to captan. Unfortunately, regulatory changes and the loss or restriction of other fungicides have left few viable substitutes, particularly in situations where fungicide resistance has developed or is likely to develop in blueberry pathogen populations.
In recent years, fungicide-resistant fruit rot pathogens, including Colletotrichum spp. (anthracnose ripe rot), Botrytis spp. (blossom blight and fruit rot), and Alternaria spp. (fruit rot), have been documented in blueberry production areas in the southeastern United States. In some cases, control failures have been reported with commonly used fungicides such as Pristine® (pyraclostrobin + boscalid), Switch® (cyprodinil + fludioxonil), Miravis® Prime (pydiflumetofen + fludioxonil), Elevate® (fenhexamid), and Abound®/Quadris® (azoxystrobin). Under these conditions, research trials conducted by the University of Georgia–Tifton Fruit Pathology Laboratory have shown that captan — used alone or in compatible tank mixes with single-site fungicides — can provide effective control of fruit rot diseases.
Ziram has historically served as one of the few comparable alternatives to captan. Like captan, ziram is a multisite fungicide with broad-spectrum activity and low resistance risk. However, regulatory pressures and anticipated product cancellations have led to reduced manufacturing, resulting in limited supplies for the 2026 season. As a consequence, reliance on captan is expected to increase across major blueberry-producing regions.
In the Northeast, for example, growers in New Jersey are being advised to judiciously incorporate captan along with fluazinam into fruit rot management programs to address emerging Colletotrichum species associated with anthracnose fruit rot.
Growers in the Southeastern U.S. with questions about disease management and fungicide recommendations should consult the Southeast Regional Blueberry Integrated Management Guide, their local Cooperative Extension agent, or state Extension specialist. As always, the pesticide label is the law and it is imperative to follow all directions, rates, precautions, and restrictions specified on the product label.
