Identifying and Treating Fire Blight in Pear Trees
Fire blight is one of the deadliest diseases found in apple and pear trees. It strikes during many phases of the tree's growth and flowering. Outbreaks can occur anywhere but are especially prevalent in the northeastern United States, where periodic outbreaks affect both commercial and backyard orchards.
Signs of Fire Blight
Fire blight is easy to recognize. If fire blight occurs during the treeís flowering stage, the blossoms turn gray-green or brown and fall off before pollination. During other stages of growth, new or existing branches turns black and wilts into a noticeable crook-shape, like a shepherdís staff or a candy cane. If the tree has already set fruit, the fruit either develops black or dark brown cankers, which slowly grow to envelop the fruit itself, or the fruit blackens quickly, shrivels, and falls off the branches.
What Causes Fire Blight?
Fire blight is caused by a bacterium called Erwinia amylovora. This particular bacterium affects apple and pear trees as well as other edible fruits such as raspberry and quince plants. It can also affect Cotoneaster, mountain ash, and hawthorn trees.
As bacteria spreads throughout the tree, it may push up through cankers or sores in the bark that exude a sticky sap. The sap carries the bacterium. Insects pick up some of the sticky, bacteria-filled sap as they visit the trees and transfer it to new trees. They can also transfer it through sucking in the infected sap and moving on to a healthy tree. New trees are infected through breaks in the bark as well as through flowers.
It's also possible to purchase trees whose rootstock have been infected with Erwinia amylovora, although the chances of such an infection passing unnoticed among commercial nurseries is unlikely. Most commercial nurseries and growers are well aware of the signs and symptoms of fire blight, and take great care to discard infected plants and minimize the risk of infection in their orchards.
How Can You Prevent Fire Blight in Pear Trees?
It is almost impossible to prevent fire blight in pear trees. Most pear varieties are somewhat susceptible to fire blight, although the Cornell University Integrated Pest Management website reports that Seckel is somewhat resistant to fire blight. The trick to managing fire blight is to monitor your pear trees and take active steps to treat the first signs of fire blight.
How to Treat Fire Blight in Pear Trees
It's important to maintain good horticultural practices throughout your garden and among your orchard trees. This includes removing diseased fruit, raking up and discarding shed leaves in the fall, and keeping your trees on a regular spraying cycle according to the trees and the recommendations from your local Cooperative Extension office. The cycle for spraying trees varies according to the type of trees and your local gardening zone.
For those who wish to avoid commercial sprays, organic sprays and oils may also be used to keep plants healthy and repel harmful diseases and insects.
If you notice fire blight among your pear trees, you can take several steps to prevent it from spreading or claiming the life of your tree:
- Avoid using nitrogen-heavy fertilizers, which encourage rapid shoot growth on trees. Rapid shoot growth seems particularly vulnerable to fire blight.
- Prune out signs of disease during the summer and during the treeís dormant season. Make cuts 8 to 12 inches below the last sign of infection to remove all potential sources of infection.
- Clean pruner blades with rubbing alcohol or household bleach between cuts. This prevents the spread of bacteria.
- Bag and discard diseased shoots in the trash, not in the compost pile.
- Control for insects with sucking mouthparts that can easily spread the bacteria. This includes controlling for aphids and pear psylla.
- Use a copper-based fungicide at the green-tip stage to reduce outbreaks.
Commercial orchards infected with fire blight are often treated with antibiotic sprays, but these are expensive and potentially too costly for home gardeners. By trimming out diseased branches, cleaning your tools between pruning sessions, picking and discarding diseased fruit, and monitoring your trees regularly, you can take many steps to minimize the impact of fire blight on your pear trees. You may not be able to avoid it entirely, but you may be able to save your trees so they can flourish for many years to come.