Apple scab, caused by the fungus Venturia inaequalis, is one of the most economically devastating diseases facing apple growers in the Northeast. Managing it has long depended on regular fungicide applications—and for many growers, that means spraying on a weekly calendar schedule using broad-spectrum synthetic multi-site fungicides like captan and mancozeb. But two new peer-reviewed studies from Cornell AgriTech suggest there may be a smarter, more sustainable way.
The companion studies, both published in Plant Disease by Līga Astra Kalniņa, a former graduate student, and Kerik Cox of the Section of Plant Pathology and Plant-Microbe Biology at Cornell AgriTech in Geneva, demonstrate that disease forecasting tools can help growers reduce their reliance on synthetic multi-site fungicides, and that biopesticides can serve as viable substitutes in well-timed spray programs.
“A lot of growers feel the need to spray every week,” said Cox. “But our research shows you can be more responsible with your fungicide use if you apply using disease forecasting. A forecasting model can help you save money and reduce the frequency of application.”
The regulatory landscape is adding new urgency. Captan and mancozeb—the two most widely used multi-site synthetic fungicides in apple production—face growing scrutiny. These chemicals have been flagged for a range of concerns, including potential reproductive and developmental toxicity, probable carcinogenicity, and reduced soil microbial activity. They have already been phased out in Europe and Canada, and the U.S. EPA is pursuing significant restrictions.
"Growers are trying to figure out how they’re going to manage diseases without these products," said Cox. “Captan and mancozeb have a long residual—they last a while and they can weather rain, which we get a lot of in the Northeast. So growers understandably rely on them. But by using disease forecasting along with well-designed biological materials and targeted single-site fungicides, we believe growers can move away from these broad-spectrum synthetics.”
What the Studies Found
The first study, published in Plant Disease, tested whether disease forecasting tools—including Cornell's NEWA (Network for Environment and Weather Applications), RIMpro (a disease modeling platform), and weather services (cell phone app)—could be used to time fungicide applications more precisely than a standard calendar schedule. Kalniņa and Cox compared several spray programs on Jonagold and Empire apple varieties, swapping out synthetic multi-site fungicides for biopesticides and relying on forecasting models to determine when to spray.
On Jonagold, no significant differences in disease control were observed among any of the programs—calendar or forecasting-based, synthetic or biological. For the more scab-susceptible Empire variety, the extended-season program using NEWA-based timing provided the best results.
The second study, also published in Plant Disease, explored how modern planting systems—specifically super spindle or high-density fruiting wall designs—might further support this transition. These systems train trees into narrow, hedge-like walls roughly 12 feet tall and three feet apart, rather than the traditional large Christmas-tree shape. The smaller canopy reduces humidity around the fruit, which in turn reduces disease pressure. Though the planting system effect was not consistent across all years, the study again found no significant differences in disease control between integrated biopesticide programs and conventional synthetic ones.
Cox acknowledged the studies have limitations. Because the programs always included some form of protectant—either synthetic or biological—the researchers could not isolate the effect of either one alone. “I can’t say for certain that using captan or a biopesticide was better, because we never had a window where nothing was applied,” he said.
“The bottom line is that disease levels were incredibly low when we used the forecasting-based program I’m proposing. And if growers are going to apply something during low-risk periods anyway—as they should, for resistance management—biopesticides are the more environmentally responsible option,” Cox explained.
The results are also a meaningful validation of Cornell’s NEWA network, developed in partnership with the Northeast Regional Climate Center. “This is a big win for NEWA,” said Cox. “We were able to use it the way a grower would and scientifically demonstrate that it’s a good tool. It’s been validated by peer-reviewed research and can be very effective when implemented in real-world conditions.”
Recommendations for Growers
Cox’s advice to New York apple growers starts with the basics: invest in good horticulture. That means planting high-density fruiting wall systems and choosing varieties with strong disease resistance. “Modern planting takes a tree and keeps it small and thin—maybe 12 feet tall, three feet apart, trained like a hedge wall rather than a Christmas tree,” he said. “That alone reduces the conditions that favor disease.”
From there, he said, growers should lean into forecasting. “Stick to our newer disease forecasting systems. Watch the weekly updates. Keep an eye on Cornell Cooperative Extension alerts for your region. And get a weather station on your farm.” With those tools in place, he believes growers will be well positioned to move away from synthetic multi-site fungicides and toward a more sustainable future.
Christina Szalinski is a freelance writer for the College of Agriculture and Life Sciences.
