Why Dry Conditions Are Best When Applying Biopesticides
August 27, 2021 
Biopesticides have fared well in Cornell University trials in the treatment of gray mold, especially when applied during dry weather.
Photo by Scott Bauer
Agility is vital to the success of biopesticides on berries, particularly with regard to the when and where of applications, according to Cornell University Associate Professor Kerik Cox.
“Biopesticides can be effective,” he says. “Time them appropriately. If you have a disease forecasting model, use it. 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 can be used if the forecast calls for drier 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 covered production systems and disease forecasting, 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 of cover often outweigh the disadvantages, and covered production makes a great stage for looking at biopesticide programs,” Cox says.
Gray Mold/Anthracnose Trial
Year 1 of trials that 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 multi-week experiments occurred during wet portions of the season from April to December.
“Yes, the disease incidence is quite high in those wet months — up to nearly 100% — but in dry months you can actually do a lot, and I believe there is no statistical differences between the biopesticides and the hard-hitting conventional product,” Cox says. “So, if it’s another drought year/seaspon, it’s a good opportunity.”
Year 2 of trials 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, reaching 10% incidence. Yeah, the conventional did better, but we’re really talking about a difference of maybe 6% incidence vs. 10%. Really not that biologically relevant,” Cox says.
Gray mold was far more intense — 60% incidence — in 2019. In turn, the conventional fungicide program was more effect over the organic program, 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 lead to 100% disease incidence. It’s a tougher year for both products.”
Conventional program 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 (Bacillus subtilis, Syngenta/Novozymes), and Serifel (Bacillus 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 to spray, just because mixing, applying, and cleaning 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 use,” Cox says. “They will help you get at some of the pathogens 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 relay on biologicals, Cox says. In general, biorational materials have better consumer acceptance and appeal these days, he says, “particularly in specialty markets.”
“Remember, there is always going to be increased acceptance by laborers and consumers. If 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.
Subscribe Today For
