Fire Blight Facts Every Denver Homeowner Needs To Know

Help your trees blossom and reach their full potential this spring by staying ahead of the threat and gathering all the facts you need to know about fire blight. 

Spring is here and Denver citizens are tired of bare trees, and are eagerly anticipating the return of their beautiful foliage. But, what if the return of leaves and flowers on your trees is not as triumphant as you imagine? Rather than lush greenery, your tree is plagued by blackened curling leaves? This is what fireblight looks like.

What Is Fire Blight?

Fire blight is caused by the devastating Erwinia amylovora bacteria.  The destructive bacterial disease takes over a tree quickly:

  • attacking leaves
  • turning them black 
  • causing branches to develop dark cankers
  • making twigs ooze white puss

The destruction is distinctly visible on the outside of the tree, giving the affected tree the appearance of being burned. It is critical to note that the disease is not merely cosmetic and will not go away on its own. Without any professional treatment, fire blight will kill branches and then the entire tree.

Will Fire Blight Spread to My Area?

Unfortunately, fire blight spreads in many ways and transmission is swift. Rain, wind, and pruning tools will spread fire blight from diseased to healthy trees. Here are the troubling facts:

  • 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
  • From there, it enters the flower tissue and eventually moves into the branch. 
  • Affected branches become girdled and the tissue inside dies.

The Colorado State University Extension has released a highly informative fact sheet that explains how bacterial ooze splashed by rain can also spread the fire blight bacteria. It seeps in natural openings in branches, leaves, pruning and hail wounds. 

The bottom line is that fire blight spreads rapidly and can make its way to your neighborhood in no time. Be prepared and protect your trees now!

What Can I Do Now to Protect My Trees from Fire Blight?

Once a tree is infected there is no way to completely cure it. You can do your part and be proactive by using preventative methods to protect your landscaping. Team up with our expert arborists and manage your property responsibly by following these steps outlined by the Colorado State University Extension:

  • Prune with Care: Remove all blighted twigs and cankered branches. Prune twigs and branches 8 to 12 inches below the edge of visible infection. Spreading the blight bacteria risk is lowered if pruning is delayed until mid-winter. 

End of winter and early spring 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.

  • Follow Best Tree Maintenance 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.

  • Plant Hardy Varieties: Thinking about planting new trees this spring? 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.

Which Denver Trees Are Most At Risk?

Trees that are members of the rose family are most likely to fall victim to fire blight. This commonly includes fruiting and flowering:

  • apple
  • pear
  • quince
  • crab apple
  • hawthorn
  • mountain ash trees

Do you have any of these tree species on your property? If so, the best first step is to schedule a consultation with one of our expert arborists. You should never assume that your trees are healthy. Getting an expert diagnosis early could save your trees!

The truth is that Denver and the surrounding areas have struggled with fire blight since 2014. It’s been difficult to stop because the disease spreads so easily from one property to the next. One thing you can do is talk to your neighbors and keep them informed. Working together to take preventative measures and identify the disease early is the only way to beat it!

Questioning which tree species you have on your property? Contact our friendly and knowledgeable team of certified arborists for a consultation.

What Are the Signs and Symptoms of Fire Blight?

Looking forward to coffee on the porch or spending time out in the garden this spring, enjoying the view of your property in bloom? There are certain types of bacteria and diseases that can sneak in undetected, but fire blight is not one of those. The visual effects of the disease are devastating and you will notice outward signs of infection right away. 

Be on the lookout for these signs and symptoms:


Brown or blackened leaves are the hallmark symptom of fire flight. 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.

Blackened bark is a secondary sign of the disease. 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 are a sign that the disease has spread significantly. 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.


Creamy ooze is an outward sign of the infection taking hold inside the tree. Sticky, creamy colored bacterial ooze may be prevalent on many parts of an infected tree. Ooze may appear from cankers on the tree bark or diseased twigs, even on infected fruits.

Fire-blight can also cause blossoms to drip with water discharge. 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.

Dead Appendages

Fire blight cankers become so numerous that they 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.

Dried dead fruits are also a sign of infection. Infected fruits get lesions first, then dry out. They continue to hang from the tree and do not fall.

If your tree is displaying any symptoms it is important to seek treatment ASAP! Early intervention can slow the progression of the disease and potentially save your tree.

What Treatment Options for Fire Blight Are Available? 

If you are worried that one or more of your trees is displaying symptoms of fire blight contact us today to learn more about how to treat trees for fire blight . Fire blight is only treatable in the early stages (outer tips and small growth). We have been fighting back against fire blight in Denver 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.
  • Treat with a topical spray: depending on the size and condition of the tree, an annual spray application may be effective for slowing and managing the disease. 

Fire blight is most dangerous in late spring and early summer when warm temperatures and seasonal rains promote the growth and spread of the bacteria. That’s why March-late April is the perfect time and opportunity to protect your trees with preventative care.

Contact us and create a custom care plan to fight off fire blight this spring. Get your free estimate today!