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What’s Oozing from Apple, Pear Trees in Pacific Northwest?

March 29, 2018

This agronomic image shows fire blight in a pome tree.

If you’re walking your apple or pear orchards this spring and notice something oozing from the trees, it’s a good indication fire blight is active in your orchard. Pome blocks with acres of highly susceptible varieties on highly susceptible rootstocks are experiencing more frequent and more damaging infections of fire blight across the Pacific Northwest.

As temperatures rise, bacteria that survived the winter begin to ooze from cankers on host trees. Insects are attracted to the ooze as a food source. Now carrying the bacterium, insects then feed on nectar of nearby flowers, transmitting the pathogen. The pathogen multiplies and can be further transmitted by honeybees, other insects and rain.

Fire Blight Spread

Infection and colony development, which is most rapid between 75° and 90° F, progresses through the tree as follows:

  • Rain or dew moves colonies into the floral nectar
  • The pathogen infects developing fruitlets
  • This results in death to young host tissue, which is often called “strike” and may take 21 days to be noticeable

There are several “blight hazards” that increase risk of infection:

  • Trees less than 3 years old that are being pushed for rapid growth through heavy pruning and nitrogen
  • Susceptible rootstock
  • Cultivars with long bloom periods
  • Consecutive days of high temperatures during bloom

Fire Blight Management

Effectively managing this pathogen takes a layered approach that begins in the spring and continues to winter. During the spring:

Unlike traditional fungicides, Actigard triggers natural defense mechanisms and prepares the tree to protect itself. When used in rotation with antibiotics, Actigard delivers enhanced protection from fire blight.

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