Plant Disease resistant varieties like this PrairiFire Crabapple, which is also resistant to scab, rust and mildew. Photo by K Salisbury, Taken at the Almshouse Arboretum of Bucks County Extension Doylestown PA
Perhaps you have noticed the tell-tale "shepherd's crook" on flowering pears, pyracantha, quince or crabapples in your care. According to the Penn State Extension publication on Fire Blight the "bacteria overwinters on infected plants in darkened, slightly sunken cankers. In the spring the bacteria are dispersed by insects, rain, wind, animals" and yes - pruning shears. The potato leaf hopper has been implicated in fire blight transmission specifically.
High Temperatures (70-81° F) + high relative humidity + rainfall during flowering = infection. When all this happens you have a perfect storm for infection. In the Tree Fruit industry they apply a registered bactericide before bud break to prevent initial infection, an antibiotic is also an option. Both of these treatments have been found to lead to resistant populations of the bacteria and have become ineffective for control in some cases. Of course, as with treating any disease, a varied approach is critical to ensure the disease does not become resistant to available controls. While potentially a valuable method for control in nurseries, generally chemical control is not recommended in landscape situations.
For those in the Green Industry, where it is too late to prevent Fire Blight from infecting susceptible plants, there are things we can do in the future to prevent an unsightly outbreak.
It is best to prevent the spread through sounds cultural practices in the landscape. If you have noticed the "shepherd's crook", blackened and wilted stems during flowering, blackened flower parts hanging on to the tree well after bloom or slightly sunken darkened canker on the wood that may ooze cream-colored liquid you may have Fire Blight.
Since we know Fire Blight is in the area, the first best bet is to plant disease resistant varieties of popular host plants.
In addition to planting disease resistant varieties there are some other things you can do to save yourself and your clients some landscape headaches:
- Purchase only disease-free plants. Look for symptoms of infection before purchasing.
- Do not over fertilize or prune excessively - succulent growth is highly susceptible to Fire Blight
- Remove water sprouts as they appear on susceptible species
- Remove severely infected plants
- During the dormant season prune out infected tissue, cut 6-8" below infection site, remove prunings from the landscape
- Do Not Prune infected tissue during the growing season!
Prevention of this disease in the landscape will not only make your clients happy, but will make any nearby nursery and orchard growers happy as well.