One of the topics of conversation these days on the lips of apple and pear growers across the country, especially in the Pacific Northwest — which dominates U.S. pome fruit production — is fire blight. Few orchard threats are so ominous, perhaps because the disease is so aptly named, with entire trees looking like they were torched — much like those in the region’s well-publicized wildfires this past year.
For organic growers, who haven’t had access to antibiotics for several years, fire blight is especially thorny. That too is a major consideration in the Pacific Northwest, which produces 90% of the nation’s organic apples, said Anna Wallis at this year’s Biocontrols USA West Conference & Expo, held last week in Portland, OR. Wallis is a Ph. D. Student at Cornell University in New York, where she said fewer than 10 of the state’s farms produce organic apples.
It’s not the heat, it’s the humidity. Fire blight infections require a wetting event to wash the bacteria into open flowers, and New York has a lot more of those during the growing season than Washington and Oregon. Wallis went over the specific products they have tried in New York, both conventional and organic. While antibiotics provide the highest level of control, biologicals are effective against lower inoculum levels, though performance does vary from season to season.
Wallis said growers are really going to have to be on their toes in the coming years, because it appears fire blight may only get more challenging to control, mainly because of five emerging factors:
- Increasingly high-density plantings of 1,200 trees per acre or more.
- Trees are being brought into production earlier, with a more protracted bloom and vigorous susceptible shoot tissue.
- New popular scion varieties are susceptible.
- Resistant rootstocks are not always helpful.
- Warmer weather from bloom to terminal bud set.
One key point Wallis emphasized is that biocontrols aren’t just for organic growers, not by a long shot. Antibiotic resistance is becoming more of an issue, so conventional growers should take a fresh look at biocontrols for a synergistic approach.
“Biologicals can be used with antibiotics in conventional orchards,” she said, “improving the performance of both.”
Stink Bugs Formidable
As most growers know, brown marmorated stink bug (BMSB) has become a national problem. It’s definitely become established in the Pacific Northwest, said David Lowenstein, a Postdoctoral Research Associate at Oregon State University who discussed integrating biological control into BMSB.
Because it’s not uncommon for BMSB to move several miles on a single summer day, Lowenstein said biocontrol in the form of a parasitoid is especially desirable. Because of that, Lowenstein has been studying the samurai wasp, an egg parasitoid that has shown 75% BMSB parasitism. The wasp was introduced in Washington in 2015 and Oregon in 2016, and has since become established, which was welcome news.
“We knew it was overwintering, but we didn’t know exactly where,” he said, which spurred investigation.
What he found was that samurai wasps spend their winters in bark, often in woody trees adjacent to orchards. They need that natural woody habitat, which he noted is not the greatest news for almond growers, who often farm in areas where there is little such habitat. However, for growers in much of the rest of the country, who are often surrounded by forest, samurai wasp may be welcome indeed.
Lowenstein said growers interested in integrating biocontrol in their orchards should take the following factors into account:
- Consider the time when pest damage is greatest.
- Will it coincide with peak (generally in summer months) populations?
- For direct release in orchard, avoid insecticide application for two weeks.
- There is the tradeoff of softer insecticides vs. efficacy and frequency of application.
Rounding out the Fruit and Biocontrol Session was Michael Dimock, Vice President, Field Development for Certis USA, who provided a much-needed overview of biopesticides in the management of pests and diseases. Sometimes growers need to get back to basics especially since biopesticides, though quickly emerging as an indispensable tool for both conventional and organic growers, are often poorly understood.
First off, Dimock says it should be noted this is a burgeoning industry, and there are now more than 400 EPA-registered biopesticide active ingredients. All are derived from natural materials, offer non-toxic (or very specific) modes of action, and are inherently less toxic than synthetic chemical pesticides.
However, it’s important to note that not all so-called natural pesticides are regulated as biopesticides, including pyrethrins, spinosyns, strobilurins, avermectins, and antibiotics, which are considered chemical pesticides. In addition, not all EPA biopesticides are from biological sources, including kaolin clay, synthetic pheromones, bicarbonates, and silicates.
Many biopesticides are of course allowed in organic crop production, but not all, such as those that are genetically modified. Also, some products are organic, but not biopesticides, such as some sulfurs and coppers, paraffinic (mineral) oils, and peracetic acid/H2O2.
“But what many don’t realize is most biopesticide use is in conventional crops,” Dimock said.
All growers employing IPM programs can realize the benefits of biopesticides, he said, including the reduced risk of adverse effects for not only workers and consumers, but fish and wildlife, and pollinators and other beneficials. Flexibility in crop and harvest management is another advantage, especially the fact that there are minimal re-entry intervals and posting requirements, and many are exempt from residue tolerance — no maximum residue level (MRL) worries. Resistance management becomes easier because biopesticides offer multiple, unique, and non-toxic modes of action; low risk of cross-resistance with conventional pesticides; and you can tank-mix or rotate to manage resistance.
Finally, Dimock offered the following considerations for using biopesticides, chief among them that they are preventative or early curative treatments, and few stand alone:
- Live microbials need time to colonize the plant or infect the host.
- Induced resistance is most effective if triggered pre-infection (priming).
- Early larval stages of insects are most susceptible.
- Infection or IGR processes may be slower than chemical pesticides.