Fireblight - Erwinia amylovora

   

HOSTS: Apple, pear, quince, crabapple, cotoneaster, hawthorn, mountain ash, pyracantha, serviceberry, and other species in the rose family.

DESCRIPTION: Blossoms first appear water-soaked, then black and shriveled. Blighted twigs curl to form a characteristic "shepherd's crook". Leaves quickly die, blacken, and remain attached to the limb. Infected fruit is shriveled and dried. As the disease progresses, it affects older, larger limbs. Cankers are usually discolored, sunken, and defined by a narrow, raised margin. Amber-colored ooze is usually present at infected buds, twigs, and cankers.

LIFE CYCLE: Fire blight develops in three phases:

Blossom blight occurs when flowers are open with stigmas and petals intact during wet weather >65°F. Canker blight occurs when the fireblight bacteria that overwinters on cankers from the previous year renew growth and infect new healthy bark tissue during wet weather >55° F.
Canker blight usually occurs during warm wet weather 1 – 2 weeks after apple trees stop blooming.
Shoot blight occurs when bacteria invade the tips of new shoots (the tip and youngest 3 leaves are most susceptible) during wet weather >55° F. Shoot blight occurs after the appearance of blossoms and/or canker blight symptoms when shoots have 10 – 12 leaves. Frost, wind, or hail can worsen fireblight infection.

CONTROLS: See Apples - Disease Resistant Cultivars!

Biological: Pseudomonas florescens (Blight Ban) sprayed when blossoms begin to open has helped reduce the blossom blight stage of fireblight. Streptomycin can be sprayed during bloom if fireblight infection periods occur. Two applications have proven to be more effective than one. (Listen to the Pest Alert Phone Line for information on infection period.)

Cultural: Prune out and destroy infected shoots and branches on a hot sunny day. Temperatures above 90°F stop fireblight infection. Remember to sterilize pruners between each cut. Keep irrigation water off of trunks, branches and leaves. Avoid excessive nitrogen fertilization.

Chemical: Dormant: Bordeaux mix sprayed as buds begin to break helps prevent infection. Spray after pruning. After bloom: Copper can be sprayed when fireblight infection periods occur. Do not spray copper during bloom.