Fire Blight showing up
Calls have been coming in that fire blight is showing up in apples, crabapples and cotoneasters. Fire blight is a bacterial disease of apples, crabapples, cotoneaster, mountain ash and pears and to a lesser degree, Juneberry and hawthorns. Left untreated, the disease will kill the affected tree or shrub.
The appearance of the disease on the affected tree is quite distinctive. The leaves will turn reddish brown and will not fall from the tree. They have the appearance of having been exposed to fire, hence the name. The leaves will hang of the tree all summer and fall. Many times the end leaf or leaves will curl back in a “shepherds crook” looking manner.
Prevention is the first line of defense against fire blight.
– When planting apples, crab apples and pears, select varieties with the most resistance to the disease. There is great variability of fire blight resistance with different varieties, especially apples. Most apple sellers have the resistance information on the plant labels.
– Avoid the heavy use of nitrogen fertilizer as this promotes rapid growth which is most susceptible to fire blight.
– Do cosmetic and corrective pruning when the trees are dormant.
– Spray with a streptomycin-based pesticide when the trees first begin to bloom. Repeat spraying every three to four days until the end of bloom. Do not spray fruit.
Once the plant has the disease, pruning out the affected material is the most effective control. If the disease is moving rapidly down a branch, pruning can be done in the summer. Otherwise, pruning is best done in late fall or in early spring. It is important to cut about 10-12 inches below the last visible sign of fire blight. It is equally important to dip the pruning shear in a mild bleach solution mixed at one part bleach to 10 part of water. (Be sure to rinse the shears well after pruning to remove residual bleach.) Pruned branches should be burned or buried.
In the case of cotoneaster hedges, selective pruning may not be the best management tool. If the disease is wide spread in the whole shrub or hedge, wait until late fall to prune. Then, rather than selectively pruning out the diseased wood, cut the whole plant/hedge down to within 6 inches of the ground. The hedge will regrow quickly the following year since it has a large root system and large energy reserve to use.
Ken Eraas is horticulture assistant with NDSU Extension Service/Ward County. He can be reached at kendell.eraas @ndsu.edu.