Why are my trees turning brown? It could be Fire Blight.
CAUSE:
Fire blight is caused by a bacterium, Erwinia Amylovora. Over the winter, bacteria hide out in bark lesions on trees and shrubs. When spring arrives with warm, wet weather, the bacteria "come alive" resulting in ooze that comes out of the localized dead areas (cankers). This ooze containing the bacteria is spread by pollinators like birds and bees, as well as by water and humans. In 1-3 weeks, the symptoms of fire blight become apparent.
AFFECTED SPECIES:
The one positive thing about fire blight is that it only affects rosaceous plants, meaning they are members of the rose family.
The bad news is that family includes more than 70 different types of plants including St. Louis favorites: pear (Bradford pear, Cleveland pear...), apple (crabapples...), rose (knock out roses...), Spirea, mountain ash, and pyracantha (which no one likes anyway).
SYMPTOMS:
Leaves wilt suddenly, turning brown and black, giving the appearance of having been scorched by fire. (fire blight...get it?) Eventually, the darkened tips will curl over to form a 'shepherd's crook'.
The bark is also noticeably discolored in areas where tissue is dying and the wood may split. In these areas where the wood beneath is exposed is where the source of the infection (remember the ooze?) is held.
PREVENTION & CONTROL:
This is a tough one. At the point we are at in summer 2014, many trees and shrubs (especially the pears and crabapples) are so infected that treatment for them is not economically responsible.
For valued species, some treatment plans exist. In early spring before flowering, prune the branches at least 6 inches below the visibly infected areas. It is VERY important to sanitize your pruning tools between each cut using Clorox, bleach or rubbing alcohol.
Bordeaux mixture may be used if you really want to save a particular tree or shrub. This again is a spring treatment done prior to buds opening and during flowering at about 4 day intervals, making treatment a very pricy option.
Applying copper sulfate when trees are dormant (very early spring) could help reduce the number of bacteria present in the dead areas of the bark, twigs, branches or trunks.
These solutions typically do not prove to be cost effective or a curative, and likely the symptoms of the disease will return in the next season.
SOLUTIONS:
After removing the infected specimen, look to replace it with something that is not part of the rose family. Some plant groups have resistant cultivars.
There are many choices when it comes to planting and Dowco is happy to help you select a species that will work well for your landscaping!
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