Arborcare-Arborscape, Inc. 2015
Fireblight is caused by the bacteria Erwinia amylovora. This bacteria attacks species of plants from the Rosaceae family including cotoneaster, roses, and mountain-ash, but fireblight causes the most damage on flowering pears, crabapples, apples, and pears.
Fireblight is spread by rain, wind, insects, bees, and contaminated tools, and it enters the plants through wounds and natural openings. Fireblight begins with terminal dieback, which leads to major dieback and eventually death. The newly infected twigs turn watery, dark green, and sort of oily. As the twig dries out it darkens and looks scorched, hence the name fireblight. The ‘burned’ looking terminal growth often bends over like an upside down ‘j’. the blossoms of the infected plants are water-soaked and turn brown. Leaves will brown or blacken and a milky, tan ooze will sometimes appear.
The movement of the bacteria to the branches causes sunken, water-soaked areas that will crack. A white to orange gummy ooze appears on these cankers. This is where the bacteria over-winters. As the canker grows it can girdle and eventually kill the tree. When on fruiting trees the fruit will get rotten areas that turn brown or black. The entire fruit will eventually die and shrivel, remaining on the branch.
The methods of control begin with sanitation. It is very important to remove and destroy infected twigs and limbs. This should be done only during dry weather to help prevent the spread of the bacteria. Pruning tools need to be sterilized between every cut as well to prevent the spread of the bacteria. Cosmetic pruning of susceptible plants should always be avoided in the spring. This can cause succulent new growth that is more susceptible to fireblight.
There are some varieties of many of these plants that are resistant to fireblight that can be used for new plantings. There are a few chemicals that can be used to control fireblight. These chemicals can provide some preventative control, however these other methods of control must also be applied for best results.
We offer fireblight sprays as treatments, often performed as the plants are in bloom. We can also fertilize the plants, using a slow-release fertilizer that can benefit the overall health of the tree or shrub, as well as encourage recovery from dieback that may have happened previously.
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