Good Fruit Grower

February 15

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34 FEBRUARY 15, 2015 GOOD FRUIT GROWER A pple growers use two chemical tools to control fire blight: antibiotics to suppress growth of the bacterial pathogen Erwinia amylovora, in its blossom blight phase and also later in the season, and Apogee (prohexadione calcium) to slow down and toughen tender growth during the shoot blight infection phase. Neither is available for use by organic apple growers. Apogee never was, and now antibiotics won't be either, offi cially as of last fall. That's going to make it tough for organic growers, especially those outside the desert climes of the West. Instead, they will be left with control programs based on cultural methods (lots of pruning), copper materials, and several biological products, the best being Serenade Optimum, which is only 50 percent as effective as streptomycin, an antibiotic that provides conven- tional growers 90 to 95 percent control of fire blight, according to Dr. George Sundin, Michigan State University plant pathologist. In Sudin's tests of Serenade Optimum, which is used like streptomycin—sprayed on during blossom time—only 42 percent control was achieved. Another material, Blossom-Protect, works well in the West, Sundin said, but New era in FIRE BLIGHT can spread quickly S cientists know quite a lot about fi re blight. Its basic source is in cankers from previous infec- tions. The bacteria overwinter there. As the canker begins to ooze in spring, bees and other insects are attracted and physically move the bacteria to blossoms. Wind and rain add to the movement. Fire blight bacteria multiply rapidly and increase to huge num- b e r s — " m i l l i o n s o n fl owers, even billions in ooze drops, in an area no bigger than the head of a pin," said Michigan State University plant pathologist Dr. George Sundin. "Temperature regu- lates the division time," he said. Bacteria can double in number in 16 to 24 hours when tem- peratures are in the 50s, in 6 to 12 hours when temperatures are in the 60s, and in 1 or 2 hours when temperatures are in the 70s. Higher temperatures slow it down. "Erwinia always grows better than the competi- tion," he said, something to remember when using biological products that compete for space in the apple blossom. —R. Lehnert Diseases control Organic growers face future without antibiotics for fi re blight control. by Richard Lehnert FIRE BLIGHT TJ MULLINAX/GOOD FRUIT GROWER The federal government is spending hundreds of thousands of dollars for research into non- DQWLELRWLFFRQWUROVIRU¼UHEOLJKW "Erwinia always grows better than the competition." —George Sundin

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