Issue link: https://read.dmtmag.com/i/275392
22 MARCH 15, 2014 GOOD FRUIT GROWER www.goodfruit.com Crop Management rganic apple and pear growers are being urged to test new strategies for controlling fire blight this season, as this is the last time they'll be able to use antibiotics as a fallback option. Organic growers have been allowed to use antibiotics in the past, but the National Organic Standards Board has voted to remove the antibiotics oxy- tetracycline and streptomycin from the allowed list of synthetic materials, effective this fall. Scientists in Washington, Oregon, and California have been working to develop alternatives for organic growers with funding from a U.S. Department of Agriculture grant. Fire blight is a serious bacterial dis- ease that can kill trees and spread rapidly through entire orchards. Fire blight infections begin in blos- soms when large numbers of cells of the pathogen Erwinia amylovora build up on the stigmas and are washed down by rain or dew into the floral cups, where they enter the developing fruitlets via the openings from which nectar is secreted. Because heat affects how quickly the pathogen builds up on stigmas, tempera- ture-based models, such as CougarBlight, are used to assess the risk of infection. Antibiotics are powerful enough to con- trol the pathogen when a model indicates that it has built up to high numbers on the stigmas. However, some biological controls will need to be applied before the risk of infection is known because they work by colonizing flowers and pre- venting fire blight bacteria from building up. For example, the yeast Blossom Pro- tect (Aureobasidium pullulans) will need to be sprayed at least once between 80 percent to full bloom regardless of what the model says, according to Dr. Ken Johnson, plant pathologist with Oregon State University. Johnson has been developing an inte- grated nonantibiotic control strategy using materials that stop the fire blight pathogen from growing on the stigma followed by those that suppress the pathogen when it reaches the nectary. Lime sulfur Johnson believes that apple growers will find it less difficult than pear growers to control the disease without antibiotics because apples are less susceptible than pears and because many apple growers use lime sulfur to thin their crop during bloom. Lime sulfur is toxic to the fire blight pathogen and also lessens the potential for infection by reducing the number of flowers. Apple growers using biological mate- rials to control fire blight should apply them after lime sulfur sprays, as sulfur is also toxic to biocontrol agents. Johnson reports that, in tests, lime sulfur applied at 20 percent and 70 percent bloom, fol- lowed by two Blossom Protect treatments at 80 percent and full bloom, provided as good control as streptomycin. An organ- ically approved soluble copper or the fungicide/bactericide Serenade Opti- mum can then be applied to target the pathogen in the floral cup. Blossom Protect grows well on flower stigmas and is spread from flower to flower by insects and so can provide 1615 W. Ahtanum • Yakima, WA 98903 • 509-248-8785, ext. 612 For the representative nearest you, visit our Web site: www.orchard-rite.com Get the Orchard-Rite® story from your nearest representative: I have been farming since 1974, and currently grow 70 acres of cherries. Last year, we put in two Orchard-Rite® Wind Machines, giving me frost protection on about 40-45 acres. We had a very cold, wet spring. These wind machines were very beneficial. Because of our Orchard-Rite® Wind Machines, we actually had our best crop in what would normally be the poorest-producing portion of the orchard. We are installing two more wind machines this year. The Orchard-Rite crew is great to work with. Anytime I've called for information or assistance, they have been Johnny-on-the-spot. Don Nusom Gervais, Oregon "The Orchard-Rite crew is great to work with." "The Orchard-Rite crew is great to work with." Orchard-Rite® Wind Machines • www.orchard-rite.com Fire blight control without antibiotics Lime sulfur and fish oil can help as part of an integrated strategy. by Geraldine Warner I n-depth information can be found at www.trfrec.wsu. edu/pdfs/P2850.pdf.