By David Eddy, Editor, American Fruit Grower
Kerik Cox knew he was onto something. The Cornell University Professor of Plant Pathology had done biopesticide trials on strawberries in 2021 and ’22, and wondered if growers could use biopesticides in conjunction with single-site fungicides instead of multisite chemical protectants, such as captan, mancozeb, sulfur, and copper.
Multisite fungicides are valued for their ability to target many different genes inside a fungus that can attack small fruit crops. But regulators, retailers, and most important, consumers, frown on them. Growers have told Cox that they are especially interested in reducing their use of captan due to injury concerns.
“They're not going to get anything else. They're going to go in and kill that fungal pathogen because it's so specific to specific proteins and gene targets.”
In 2023 he conducted another trial involving day-neutral ‘Albion’ strawberries planted 12 inches apart in double rows. As in the two previous trials he found that biopesticides also have multisite mode of action. Using this approach could help growers from getting resistance to the single-site fungicides. In addition, the residuals of multisite fungicides, unlike biologicals, can remain in the environment for a long time.
Cox says biopesticides can still harm non-targets as well, but their environmental impact is greatly reduced. Historically, that's also made them poor performers in the eyes of many. But if you can use disease forecasting, you know exactly when they need to go on, they do their job, and then they're gone.
Combining the biopesticide with the single-site fungicides will target one gene in a fungus, or even one enzyme or an enzyme pocket, which is a little tiny protein, Cox says. In that they’re like the antibiotics that you would get from the doctor, highly specific only to fungi, not people.
“They're not going to get anything else,” he says, “they're going to go in and kill that fungal pathogen because it's so specific to specific proteins and gene targets.”
Air It Out
Synthetic multisite fungicides are popular because they are effective, and because they work in most conditions. Growers can cut corners, they don’t need a well-designed, neatly maintained planting.
“The trees were so small, so open, and so reduced in canopy that the air is going through and stopping them from getting apple scab without any sprays at all.”
“If you have a trashy planting, you're going to get disease, and you would need to rely on heavier fungicides. If you have a wet planting, same thing,” he says. “But if you can make it dry, biopesticides will excel, and we're seeing that this season right now in New York. We have an incredibly wet season and you can see different plantings struggling, depending on how big and bushy they are. If you put it on in a monsoon, it's going to get disease.”
Cox realized this first hand when he inherited apple orchards, which were farmed in the old style, meaning the trees were really big and bushy. They suffered from a common malady in the Eastern U.S., apple scab. As he began planting newer open high-density orchards, a lightbulb went off as he found they were much less likely to get apple scab.
“The trees were so small, so open, and so reduced in canopy that the air is going through and stopping them from getting apple scab without any sprays at all,” he says. “And then I was like, ‘Wait a minute.’”
That's why organic farming is so much bigger in the Western U.S. where the climate is generally much drier and apple scab is rare, Cox says. In such a situation, where a fungal infection is much less likely to take hold because of the lack of moisture, it raises the following question: Are biopesticides effective as a stand-alone material for fungal infections?
The best way for fruit growers to avoid fungal infections is to take excellent care of their orchards and vineyards. It may sound basic, but Cox says it’s critical to allow for air flow so there is less moisture. It’s also important not to have “junk” in the orchard, which means essentially everything except the plants, such as mummies or cuttings left behind, may be infected with fungi and bacteria.
Good field sanitation practices are important, though Cox says the problem is they take a lot of labor, which growers either cannot access, or even if available is not affordable.
“If you had a lot of labor, you could do all kinds of production and inoculum reduction practices,” he says, “and then you don't need as many applications to sort of beat the system.”
For example, a lot of apple and pear growers struggle with fire blight fungal infections, so-named because a serious case can leave an orchard looking like it has been burned. Antibiotics have proven effective, and have been found to work best in conjunction with biopesticides, which raises another question: What should you keep in mind when using an antibiotic in conjunction with biopesticides?
However, Cox says many fear we already have an antibiotic crisis in medicine. He was recently at a veterinary medicine conference where concerns about bacteria evolving were discussed.
“And the next thing you know, you have resistant bacteria on a fruit going into someone's body, so the antibiotics are a lot more terrifying in that sense,” he says.
Fewer Choices
Cox says another big reason for continuing to explore alternatives to synthetic multisite fungicides is that because of off-target effects they are slowly being cancelled by the U.S. EPA. In fact, many have already been cancelled by the European Union, as well as Canadian and other regulatory agencies. He expects new such products are going to be even harder to register because they're going to come in with greater impacts.
Biopesticides, on the other hand, are booming mainly because of lower environmental impact and favorable consumer perception. Synthetic pesticides require a great deal of slow, expensive testing to get registration, while the biological products have easier and more expedited fee processes and requirements.
You can’t just spray and walk away, Cox says. First, you have to have make sure to get complete coverage, and then monitor carefully.
“It’s not something you can be hasty with,” he says. “But I think if you're careful, and you make sure you have good water and good coverage and adequate rates, it’ll work.”
It’s critical to have your orchard, vineyard, or field in top shape, Cox says. He’s met growers whose orchards were so clean and well-managed that they were probably spraying more than they actually needed to protect their crop. But there’s an important message there for growers who want to forego captan or other multisite fungicides for single-site fungicides plus biologicals.
Cox concludes: “I think if you want to do it, you have to use modern farming practices, modern horticulture, because those practices already favor an environment that's not conducive for disease, such as the high-density (short-branched) apples as opposed to the processing apple or the pick-your-own orchard where the trees are big and bushy.
Photos courtesy of Kerik Cox
