Scientists know quite a lot about fire blight. Its basic source is in cankers from previous infections.
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 numbers—“millions on flowers, 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 regulates the division time,” he said.
Bacteria can double in number in 16 to 24 hours when temperatures 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 competition,” he said, something to remember when using biological products that compete for space in the apple blossom.
After growing up on a Michigan dairy farm, Richard Lehnert began writing about farming in 1962, while still a junior studying journalism at Michigan State University. He worked at newspapers for a year before joining the staff of Michigan Farmer, where he spent 26 years, the last 15 as chief editor. He was a member of the staff of Good Fruit Grower from 2010 until 2015.Read his stories: Story Index