Turning on a plant’s defenses
New technology is coming to the apple and pear industry to help control fireblight. Actigard is a systemic compound with a unique mode of action that mimics the natural systemic-activated resistance response found in many plants. When applied preventatively, much like vaccinations are given to humans to ward off certain diseases, Actigard stimulates or induces the plant’s natural defenses, turning on the genes that are involved in fighting off infection from various diseases. Actigard (acibenzolar-S-methyl), a product of Syngenta, is registered for other crops, including tomatoes, tobacco, and berry fruits. Registration is pending for apples and pears.
In pome fruit, Actigard is applied late bloom or as a rescue treatment to help manage fireblight, said Dr. Ken Johnson, plant pathologist at Oregon State University. Research has shown improved fireblight protection when Actigard is used in combination with antibiotics, reducing strikes per tree by nearly half.
“That’s why we like Actigard—we’re cutting down blight incidence by 50 percent or so by going with a late application,” Johnson said. “In the blight business, that’s a meaningful response.”
One of the primary benefits to Actigard is its long residual life of seven to ten days during late petal fall, a time when antibiotics are ineffective, he said. “You can use Actigard late for petal fall, rat-tail, and shoot blight in susceptible cultivars—it’s like using Apogee [plant growth regulator] but with no stunting of growth.”
But he’s also excited about Actigard’s potential as an aid for fireblight tree rescue and cleanup in an orchard, especially a new, young one. And, there may be potential for the material to protect rootstocks sensitive to fireblight, though more research is needed.
Johnson has been experimenting with painting Actigard on trees after pruning branches with fireblight symptoms. In a small trial of Bosc pears (15 untreated and 10 treated trees), all trees were inoculated with the pathogen in April and the orchard then scouted for fireblight in early June. Trees with symptoms were pruned, painted, and sprayed with Actigard. Retreatment of cutting, spraying, and painting was done in late June on trees still showing symptoms. Fireblight in the control trees was cut out, but trees were not sprayed or painted. In October, the block was revisited to look for tree survival.
Thirty percent of the trees that had fireblight cut out but no Actigard treatment were lost. Where trees were cut and sprayed, about 25 percent of the trees were lost—not much better than the control with cuts only, Johnson said. But where the trees were cut and painted with Actigard, only 10 percent were lost.
“Where we painted Actigard below the cuts—about 18 inches below the cut—we reduced the amount of blight,” he said. Cuts were made about six to eight inches below the fireblight symptom.
The U.S. Environmental Protection Agency has granted a “crop nondestruct experimental use permit” label for Actigard on pears and apples for the next two years. The experimental use permit label allows Actigard to be mixed with antibiotics as a spray and paint. Up to 150 acres in Washington, 60 acres in Oregon, and 30 acres in California can be treated.
As part of the EUP permit, material used must be tracked, the department of agriculture notified (e-mail will suffice) when applied, and an administrative agent present during application. Researchers are working with industry to develop a list of qualified agents that can work with growers.
Johnson said it is important to test the material to find out how it works in real-world settings.