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pathogen Erwinia amylovora even in very small numbers. Over the past three years, Johnson has surveyed about 100 commercial orchards and found that, on average, around 9 percent of 600 flower samples he and his colleagues have collected contained the pathogen at midbloom. The likelihood of finding the pathogen at that time depends largely on how clean the orchard is in terms of old cankers, Johnson said. If the orchard started out clean, there are not likely to be enough bacteria around to warrant spraying for the disease early in bloom, he said. By full bloom, around 15 percent of 600 flower samples had bacteria, on average, and by petal fall, there was a 30 percent chance of finding the bacteria in a sample. The LAMP assay is not yet available for growers to use to find out if the pathogen is in their orchards, but quick molecular tests are being developed, somewhat like home pregnancy tests, that growers might be able to use in the future. "We're not quite at that point yet," he said. "But there are people working on that. One of these days, I think we will see someone who can offer that as a service." How does a delayed-dormant copper treatment affect the pathogen? Johnson has been collaborating with Rachel Elkins at the University of California to assess the impact of using delayed-dormant copper treatments in pears. In studies in 2010 and 2011, 14 blocks of around ten acres were split, with half of each block receiving a dormant oil treatment and the other half receiving oil and six pounds of copper per acre. LAMP assays showed that fireblight bacteria lev- els in flowers at petal fall were 50 percent lower when cop- per and oil were applied than when oil was applied alone. "I think overall, we're going to have less disease where we put on delayed-dormant treatments of copper," Johnson commented. Elkins also found that there was no more russeting in the copper and oil treatment than with oil alone. Does bloom thinning affect fireblight control? Biological controls are not compatible with applica- tions of lime sulfur and fish oil, a mixture used during bloom for chemical thinning, Johnson reported. How- ever, the thinning treatment is also toxic to the fireblight organism and, because of the damage it causes to flowers, it shortens the period when growers need to worry about fireblight control. "If you knock out flowers, they can't be infected," he said. In tests where trees were inoculated with the fireblight bacteria, two applications of fish oil and lime sulfur (at 20 and 70 percent bloom) followed by Blossom Protect (Aureobasidium pullulans) provided control on par with antibiotics. But sandwiching the thinning and fireblight treatments—with a biological control applied between the two fish oil and lime sulfur treatments—is not recom- mended, Johnson said. "You are probably wasting your money trying to put a biological between the king bloom and 70 percent bloom treatments. Worry about fireblight control after." Can the disease be controlled effectively without antibiotics? Johnson said the disease can be controlled by an inte- grated program that will require more treatments of bio- logicals than growers are used to using with antibiotics, and that will be more expensive because of having to run the sprayer more often. Bloomtime Biological (Pantoea agglomerans) or Blightban (Pseudomonas fluorescens strain A506) applied at 30 and 70 percent bloom, followed by the biofungicide Serenade Max at full bloom and petal fall are effective treatments, he said. Serenade, which contains the active ingredient Bacillus subtilis, also contains antimicrobials that target the fireblight pathogen. • www.goodfruit.com GOOD FRUIT GROWER FEBRUARY 15, 2012 19