The Denver Post reported just earlier this year about the devastating widespread effects of fire blight on trees across the Front Range. Heavy hailstorms in the Denver area had one major unexpected consequence- the rapid spread of fire blight. Trees all over the community turned pitch black, looking as if they had literally been torched!
The bacterial ooze and dark cankers plaguing trees across the Front Range is attention-grabbing and alarming, causing concerned citizens to seek out more information on fire blight. Although this infectious bacteria is not at all new, it is in rare form. Colorado State University’s Department of Horticulture and Landscape Architecture warns that this will be an epic year for fire blight. Entire neighborhoods have already been devastated!
Denver is under siege, and we’re here to help. We can protect your trees from the fire blight bacteria. Our arbor experts have a tried and true system in place, but you have to act soon. Here’s everything you need to know to stop fire blight in its tracks.
What Is Fire Blight?
Fire blight is a destructive bacterial disease. The Erwinia amylovora bacteria attacks leaves, turning them black, causes branches to develop dark cankers, and makes twigs ooze white puss. It gives the affected tree the appearance of being burned, hence the name. Left untreated, fire blight will kill branches and then the entire tree.
Is fire blight harmful to humans? It is not. If you recently ate a sour apple or pear and are worried about infection, you can relax. Like other plant diseases, fire blight only harms plants. It is harmless to humans.
How Does Fire Blight Spread?
Rain, wind, and pruning tools will spread fire blight from diseased to healthy trees. The bacteria survive the winter in cankers on already-infected branches. When temperatures warm up in the spring, the bacteria ooze out of the cankers. The sticky substance attracts aphids, ants, bees, beetles, and flies. The insects pick up the bacteria and carry it on their bodies to the blossoms of healthy plants, spreading the disease.
Once in the insect carries the bacteria to a new blossom, the in the nectar. From there, it enters the flower tissue and eventually moves into the branch. Affected branches become girdled and the tissue inside dies.
According to the fact sheet released by Colorado State University Extension, bacterial ooze splashed by rain can also spread the fire blight bacteria. It will seep in natural openings in branches, leaves, pruning and hail wounds.
Could Fire Blight Affect My Trees?
Fire blight attacks many members of the rose family, including non-fruiting apple, pear, quince, crab apple, hawthorn, and mountain ash trees. Do you have any of these tree species on your property? If so, it is vitally important that you act quickly. The Denver Post reported entire neighborhoods of crab apple trees being wiped out by fire blight!
Don’t assume your trees are healthy. The devastating disease is common and has been prevalent in Denver since 2014. Try to raise awareness with your neighbors who share tree species that are susceptible. It’s incredibly easy for fire blight to spread from one property to the next!
Not sure what tree species you have on your land? Contact our friendly and knowledgeable team of certified arborists for a consultation.
When Is the Greatest Risk of Fire Blight?
The disease is most serious when spring temperatures during pre-bloom and bloom are warmer than average. The fire blight pathogen spreads particularly rapidly during warm rainy spring seasons. The splashing rain can carry bacteria from an infected tree to a healthy one.
Blight of twig terminals can occur in late May through June during wind-driven rain events. Although spring is the most dangerous time for the spread of fire blight, hail and wind damage provide wounds that allow the pathogen to enter at other times. To effectively protect your trees, you need to treat them before the onset of spring.
What Can I Do Now to Protect My Trees from Fire Blight?
There is no cure for fire blight. However, you can be proactive and use preventative methods to protect your landscaping. Take control and manage your property responsibly by following these steps outlined by the Colorado State University Extension:
- Plant resistant varieties: Cultivars of apple, crab apple, and pear differ in their degree of susceptibility to the bacterium although some cultivars are less susceptible than others, no cultivar is immune to infection when the pathogen is abundant and conditions are favorable for infection. Avoid blight susceptible apple rootstocks especially when grafted to susceptible scions. Select varieties adapted to your growing area to minimize the stress that may predispose the tree to other disease-causing agents. Local weather conditions from year to year also affect the amount of fire blight found in a variety.
- Use best cultural practices: Minimizing rapid growth and succulent tissue will reduce the risk of fire blight developing on the susceptible young, succulent tissue. Annual pruning with avoidance of major cuts will help minimize tree vigor. Similarly, limiting the amount of nitrogen fertilizer will reduce twig terminal growth. Fertilization should be based on the results of foliar and soil nutrient analysis and should not be applied in excess.
- Prune safely: Remove all blighted twigs and cankered branches. Prune twigs and branches 8 to 12 inches below the edge of visible infection. CAUTION! After each cut, surface sterilize all tools used in pruning. Dip tools in household bleach or ethyl alcohol, or use household spray disinfectants. Spreading the blight bacteria risk is lowered if pruning is delayed until mid-winter. Winter pruning can also be accomplished more efficiently because pruning tools need not be disinfected between cuts if pruning is done when trees are fully dormant. To decrease the chance of new infections, promptly remove from the site and destroy all infected branches.
What Are the Signs of Fire Blight Infection?
Your landscaping is your pride and joy, bringing so much beauty to your property. Some types of tree disease can creep in almost unnoticed, but fire blight is not one of those. The visual effects are truly astonishing. You will begin to see outward signs of infection at the first petal fall.
Symptoms of fire blight may include:
- Water-soaked blossoms: during blossom blight infected blossoms look as though they are seeping with water and wilt right away. They do not fall, but cling to the tree, turning dark brown.
- Brown or blackened leaves: when bacteria have spread through the branch and reached the leaves, they turn crisp and dry. They curl and turn a brownish-black color, looking burnt. They stay attached to the tree.
- Dead branches: fire blight cankers kill tree branches. They show up as sunken, dark discolored areas, with a narrow callus ridge along the outer edge. These ridges differentiate fire blight cankers from other fungal tree cankers.
- Blackened bark: fire blight affects all parts of the tree, from the ground up. Bark on the trunk of the tree cankers with infection and turns black. Inner bark that is infected may turn green or brown.
- Black “shepherd’s crook” twigs: first, the bark at the base of blighted twigs becomes water soaked, then dark, sunken and dry. Infected twigs often become bent, resembling a shepherd’s crook.
- Dried dead fruits: infected fruits get lesions first, then dry out. They continue to hang from the tree and do not fall.
- Creamy ooze: sticky, creamy colored bacterial ooze is prevalent on my parts of an infected tree. Ooze may appear from cankers on the tree bark or diseased twigs, even on infected fruits.
What Treatment Options for Fire Blight Are Available?
Winter is the best time to treat trees for fire blight because the bacteria is inactive during the colder months. There will be no risk of inadvertently spreading it around. If you are worried that one or more of your trees is displaying symptoms of fire blight contact us today. Fire blight is only treatable in the early stages (outer tips and small growth). We have been battling fire blight for years.
Here is what we can do to treat fire blight in your trees:
- Trim trees: Trimming in winter is an effective way to remove heavily infected areas. Trees sustain less damage and have more time to heal when they are trimmed during winter. They will incur less stress and are not at risk of becoming further infected at this time. Once trimmed, infected trees should receive one or more chemical treatments.
- Cambistat soil injection: Cambistat is a chemical growth regulator applied Spring-Fall. It lasts for 3 years. For trees infected with fire blight, it is used to minimize shoot growth, which will minimize the shoot blight stage of a fire blight infection.
- Treat with Bacistat trunk injection: When your body has an infection, you take an antibiotic. Bacistat is an antibiotic for your trees! It can be applied yearly in April-May. We recommend treatment every 2 years to limit trunk damage. Bacistat will reduce only the twig stage, not the blossom stage of infection. Optimal results with Bacistat occur when applied prior to the onset of visual symptoms.
Fire blight is making headlines in the Denver area. Don’t let your trees become casualties as the Front Range is affected. Team up with us and keep your trees happy and healthy. Get your free estimate today!