Agriculture Reference
In-Depth Information
Symptoms.
Infected tissues become dark, take on a water-soaked appear-
ance, and may exude a yellowish-brown bacterial slime that looks like sugar
water droplets. Sunken areas appear on infected spurs, shoots, and branches.
Infected shoots and leaves turn dark brown to black and remain attached to
the trees, creating conspicuous brown flags. Infected fruits shrivel into black
mummies. Cankers girdle and kill infected stems, branches, and trunks. Be
careful in diagnosing fire blight because the symptoms are similar to those
of Pseudomonas blossom blast, Nectria twig blight, Phomopsis pear dieback,
and twig borer damage.
Management.
Grow fire blight-resistant varieties if available. In any case,
you need a multipronged approach to managing fire blight.
Remove as many fire blight hosts as possible from your orchard, land-
scape, fencerows, and nearby areas. Remove blighted flowers, fruits, and
stems as soon as you notice them, regardless of the time of year. Prune only
when the trees are dry, however, to avoid spreading the pathogen even more.
Carry a hand sprayer of Lysol (or similar disinfectant), 70 percent ethyl or
isopropyl alcohol, or household bleach solution containing 9 parts water to
1 part bleach. The disinfectants and alcohol are less corrosive to tools than
bleach.
Disinfect your tools after every cut. On cuts larger than 1 inch in diameter,
also disinfect the cut surfaces. Be sure to cut at least 12 to 15 inches below
sunken or discolored areas on the stem or other visible symptoms. The bac-
teria travel downward in the stems through the trees' vascular systems. Be-
fore starting your regular pruning, go through the orchard at least twice, re-
moving blighted prunings. Bury or burn all prunings that might be infected
with fire blight.
Maintain moderate growth in your trees. Avoid excess nitrogen, and keep
pruning to a minimum to avoid forcing lush, blight-susceptible foliage. In-
stead, use spreading and other training methods.
When thinning fruit, remove late blooms. Remove and destroy severely
infected trees if the main trunks show signs of infection; this is especially
