Why dry conditions are best when applying biopesticides

"Biopesticides can be effective," he says. "Time them appropriately. If you have a model, use a model. If there's no model out there, look at the weather forecast and see when the big rains are coming."

Because most biologicals are surface protectants, biopesticides are recommended if the forecast calls for dry weather, Cox says. If significant rainfall is imminent, fall back on a single-site conventional material, he adds.

"It can be harder for (biopesticides) to control fruit rots in very wet years, but if you combine them with cover, forecasting, and other things, you can do pretty well with them," Cox says.

Covered production benefits disease management by blocking water and wind, both of which can spread disease. On the other hand, wind can also help prevent disease by reducing relative humidity and drying time. In a more neutral sense, cover has little impact on soil, which can contain, spread, and initiate root diseases and weeds, which can harbor pathogens.

"These extra advantages often outweigh the disadvantages, and covered production makes a great stage for looking at biopesticide programs," Cox says.

DISEASE TRIAL

Year 1 of a trial Cox has been conducting at Cornell AgriTech since 2017 focused on covered production and the comparison between conventional pesticide Switch (cyprodinil/fludioxonil, Syngenta) and biopesticides LifeGard (Bacillus mycoides isolate J, Certis), OSO (Polyoxin D zinc salt, Certis), and Sil-MATRIX 1% (potassium silicate, Certis). Two of three experiments occurred during wet seasons.

"Yes, the disease incidence is quite high in those wet years, up to nearly 100%, but in a dry year you can actually do a lot. I believe there is no statistical difference between the biopesticides and the hard-hitting conventional one," Cox says. "So, if it's another drought year, it's a good opportunity."

Year 2 of the trial focused on timing by alternating conventional Elevate (fenhexamid, UPL) and Switch — a "really powerful combination to which there is not a lot of resistance," Cox says — and comparing them to what Cox calls his biopesticide "program of choice" — Double Nickel (Bacillus amyloliquefacinens, Certis) alternating with LifeGard.

"It wasn't a very heavy year for gray mold incidence in this particular instance, hitting 10%. Yeah, the conventional did better, but we're really talking about a difference of maybe 6% incidence vs. 10%. Really not that big," Cox says.

Gray mold was far more intense — 60% incidence — in 2019. In turn, the conventional treatment triumphed over organic, 30% vs. 50%.

"A wet year may not be the year you want to try biopesticides, but they can still be effective," Cox says. "It's not like the organic programs are just 100% disease incidence. It's a tougher year for both products."

Conventional treatment again fared better in 2020, although again, "not that big of a difference," Cox says — 5% vs. 15%.

DIFFERING MODES OF ACTION

Double Nickel is an antibiotic metabolite, meaning it kills microbes by producing metabolites, Cox says. Similar treatments include Serenade Opti (Bacillus subtilis, Bayer), Taegro (B. subtilis, Syngenta/Novozymes), and Serifel (B. amyloliquefaciens, BASF).

"They all work really well," Cox says. "They all of have differences in terms of their formulation, and I often recommend that you pick a formulation you like using. If it comes in a liquid, that's always my favorite spray, just because mixing and everything else is much easier and more effective. That doesn't mean powders are bad by any stretch of the imagination. It's just that liquids are really easy to spray
and mix."

Meanwhile, resistance inducers, such as LifeGard and Regalia (Reynoutria sachalinensis, Marrone Bio Innovations), work internally.

"They're getting better, getting easier to do," Cox says. "They will help you get at some of the materials inside. And if you are going after anthracnose in brambles … or if you have problems with root diseases … it would not be bad to include some of these as well."

Efficacy aside, growers — certainly organic producers — have good reason to rely on biologicals, Cox says. In general, biorational materials have better consumer acceptance and appeal these days, he says, "particularly in fancy specialty markets."

"Remember, there is always going to be increased acceptance by laborers and consumers. If you have a pick-your-own and say, 'I only use biopesticides and biorational materials,' that's just going to appeal to your customer base," he says.

Finally, "The good news is that you are not going to really develop resistance to biopesticides," Cox says.

Photo caption: Biopesticides have fared well in Cornell University trials in the treatment of gray mold, especially when applied during dry weather.
Photo by Scott Bauer

Source: Growing Produce

Source: Growing Produce