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Apples, ornamental and edible pears, crab apples, pyracantha, loquat and some other plants can get a bacterial disease called fire blight. Fire blight turns the tips of the branches black as though they were burned by fire.
Identifying fire blight:
- Infected limbs turn brown and then black at the tip. Fire blight can progress into the tree and kill it.
- The affected bark becomes sunken and eventually becomes dry and may have cracks at the edge of the area.
- The end of the branch may bend over like a shepherd’s crook. Look for this crook to identify the disease. You may not see the crook on every branch.
- Dead leaves and fruit remain on the tree and branches may ooze a dark sap.
Fire blight is often spread by insects. The insects carry the bacteria from infected to healthy plants and the bacteria enter the plant through the flowers. The bacteria can also enter through wounds on the plant.
Cultural Controls: The main control for this disease is to plant resistant varieties. Some ornamental pears are not very resistant to fire blight. They grow well until the disease finds them and then they get infected. Resistant varieties either will not get the disease or will survive once they get the disease. Look online or contact your local Extension Office for a list of varieties or see this partial list of resistant varieties.
Do not fertilize heavily with nitrogen as this may make the disease worse. Be careful about damaging the tree since the disease can enter through wounds.
Once the tree is infected, it is difficult to control this disease. Even with the best of controls, the disease may be fatal. Carefully cut out the dead branches, if you can. Prune them out 8 inches below the bottom of the brown part.
The disease is easy to spread on pruning shears. You must clean & disinfect your shears between every cut. Here are some methods to disinfect pruning shear blades from Jean Williams-Woodward, UGA Extension Plant Pathologist:
· The best method is to wipe the blades of the shears between each cut with a t-shirt or other cloth soaked in 70% isopropyl (rubbing) alcohol. Wiping the shears removes the plant sap, which actually the carries the bacteria.
· Another option is to spray the blades with Lysol disinfectant after each cut. If the blade becomes sticky from plant sap, wipe it first and then spray with Lysol so that the disinfectant can penetrate and kill any bacteria remaining on the blade.
Clean and oil your shears once you finish pruning. Collect all clippings, seal them in a bag and throw them away immediately.
Chemical Controls are generally not very effective once the disease is in the tree. Streptomycin or copper sprays are labeled to prevent the disease. They must be sprayed before the tree is infected and must be used every several days during bloom. I feel like this is not a useful tool because of these requirements. I usually do not recommend that landscapers or homeowners spray for this disease. Spraying may prevent the disease but is not useful once the tree gets the disease.
Summary: Planting resistant varieties is the best control for fire blight and it is easy to do if you plan ahead. Fire blight is difficult to control once it is in the tree. You may never completely control it once the tree is infected. Cultural practices and good sanitation may slow spread of the disease. Be careful when cutting out infected wood since you can spread fire blight throughout the tree on pruning shears.
Photos: William M. Ciesla, Forest Health Management International, Bugwood.org
Landscapers often apply a thick layer of mulch around trees in a ring. When this mulch is piled against the trunk, this is called a mulch volcano. Though this is better than having no mulch at all, mulch volcanoes can cause several health problems for trees.
Mulch helps trees in several ways:
· Controls weeds and keeps soil moist
· Moderates very high or low soil temperatures.
· Improves tree roots and overall tree health.
· Reduces trunk injury and soil compaction from equipment.
However, according to Chris Starbuck at the
1. Mulch volcanoes encourage poor root growth. Roots buried by the mulch volcano die due to lack of oxygen in the water-logged soil. At the same time, growing conditions in the top of the mulch are temporarily favorable for root growth. This causes roots to grow upward instead of downward. Mulch does not hold water as well as soil and eventually dries out. This stresses the tree’s roots and puts the tree into severe drought stress.
2. The mulch volcano can also act as an umbrella, shedding water to the surrounding soil. Fungal activity in the surface of mulch volcanoes can make the mulch repel water. Water then runs off the volcano, rather than moving into it. This usually happens more with mulches that are high in carbon like ground wood, wood chips or sawdust. It also happens with bark mulches. Since new trees have few roots the root ball must be kept moist. Volcano mulching can keep irrigation and rain from the root ball and lead to severe drought stress even if the tree has a regular water supply.
3. Mulch volcanoes encourage fungal canker diseases. Starbuck also notes that mulch volcanoes keep the base of the tree constantly moist. Trees are also stressed because the cells in the bark of the tree cannot get enough oxygen. This can cause bark decay. Finally, volcano mulching harbors termites and rodents that may attack the tree.
Once the trunk is damaged, there is usually little that can be done to reverse the damage. Avoid mulch volcanoes when mulching. Do not pile mulch around the base of the tree. Apply a two to three inch mulch evenly around the tree, preferably out to the edge of the drip line.