Hypoxylon Canker

What is a Hypoxylon Canker?

Hypoxilon Canker is a fungal disease caused by Hypoxylon mammatum, particularly affecting trees under stress. The disease is known for causing dieback and canker formations on the bark. While it primarily targets weakened trees, its impact can be significant, leading to decline and eventual death.

Host Plants

Hypoxilon Canker primarily affects hardwood trees, with specific host plants including:

Oak Trees: Particularly susceptible are members of the red oak group, including species like the red oak (Quercus rubra), black oak (Quercus velutina), and live oak (Quercus virginiana).

Hickory Trees: Various species of hickory (Carya spp.) are also known to be affected by Hypoxilon Canker.

Beech Trees: American beech (Fagus grandifolia) can host this fungus, especially under stress.

Elm Trees: Species of elms (Ulmus spp.) can also be impacted, though less frequently.

Other Hardwoods: The disease can affect a range of other hardwood species, but it is most commonly reported and observed in oaks.

Regions Impacted

This disease is common in the United States, particularly in the eastern and southeastern regions. Its occurrence aligns with the distribution of host tree species and is more prevalent in areas with stressed tree populations. Urban environments, where trees often face more stress factors, can see higher instances of Hypoxilon Canker.

Symptoms

The symptoms of Hypoxilon Canker primarily manifest on the bark and branches of affected trees. Cankers located on the main trunk have the potential to cause tree death within a period of 3 to 8 years.

Early Canker Development:

• Cankers typically develop where branches join, on stubs, around wounds, or near galls.
• Initial symptoms often start as small, discolored patches on the bark. These areas may appear slightly sunken or stressed compared to the surrounding bark.
• The affected bark might show a subtle change in texture, becoming slightly rougher or more brittle.

Fruiting Body Formation:

• As the canker progresses, the fungus develops fruiting bodies beneath the bark. These structures, initially hidden, are responsible for spore production.
• The fruiting bodies can cause the bark to crack and eventually slough off, exposing the fungal stroma underneath.

Fungal Stroma Appearance:

• The exposed fungal stroma can vary in appearance, often starting as a felt-like, silvery-gray mat that turns darker, usually black, over time. This is a key diagnostic feature of Hypoxylon Canker.
• These mats are typically crusty and can be extensive, covering large areas of the canker.

Advanced Canker Symptoms:

• In advanced stages, the canker girdles the branch or trunk, disrupting nutrient and water flow. This can lead to wilting and dieback of branches beyond the point of infection.
• Large cankers can significantly weaken the structural integrity of the tree, increasing the risk of branch breakage or tree failure.

Leaf Symptoms:

• While the primary symptoms are on the bark, affected trees may show secondary leaf symptoms such as premature yellowing or browning, especially on branches beyond the canker site.
• Leaf drop and reduced foliage density can occur as the tree’s overall health declines.

Tree Decline:

• Over time, the cumulative effect of multiple cankers and the general weakening of the tree lead to a decline in vigor, stunted growth, and an overall reduction in tree health.

It’s important to note that while Hypoxilon Canker is typically secondary to some form of stress or injury to the tree, its presence can exacerbate the decline of the tree’s health. Early detection and management of tree stress can help prevent or mitigate the impacts of this disease.

Disease Cycle

The disease cycle of Hypoxylon Canker typically unfolds as follows:

Infection Initiation: The cycle begins when fungal spores from Hypoxylon species land on a susceptible host tree. The most common points of entry are areas of stress or injury, such as wounds, branch stubs, or areas weakened by other diseases or environmental factors.

Fungal Establishment and Growth: Once the spores have settled on a suitable site, they germinate and the fungus starts to grow and invade the tree’s tissues. The fungus primarily colonizes the wood under the bark and in the cambium layer.

Canker Formation: As the fungus grows, it disrupts the flow of nutrients and water, leading to the death of bark and cambium tissues and the formation of cankers. These cankers are typically sunken and discolored areas on the bark.

Fruiting Body Development: In response to the death of the tree tissue, the fungus forms fruiting bodies under the bark of the canker. These fruiting bodies produce spores that are released into the environment.

Spore Dispersal and Spread: The spores are dispersed by wind, rain, or animal activity and can infect other susceptible trees in the vicinity. The cycle is more likely to continue in areas with a high density of stressed trees.

Secondary Spread and Expansion: The cankers can expand over time, potentially girdling the tree and causing further stress and decline. The tree’s weakened state can also make it more susceptible to other pathogens and environmental stressors.

How do you Prevent and Control Hypoxylon Canker?

Preventing and controlling Hypoxilon Canker, a disease affecting stressed or weakened trees, involves several strategies:

Maintain Tree Health: The best prevention is maintaining overall tree health. Ensure adequate watering during dry periods, provide proper nutrition, and avoid over-fertilization, which can lead to lush but weak growth.

Reduce Stress Factors: Minimize stress on trees by avoiding soil compaction, providing adequate space for root growth, and protecting trees from physical damage like lawnmower hits or construction injuries.

Prune Wisely: Prune trees during the dormant season to avoid attracting insects that can spread the disease. Always use sterilized pruning tools to prevent transmitting pathogens.

Remove Infected Limbs: Prune and properly dispose of infected branches to prevent the spread of the fungus. This should be done as soon as symptoms are noticed.

Sanitation: Clean up and dispose of fallen branches, dead wood, and leaf litter from around the tree to reduce the habitat for the fungus.

Monitor Regularly: Regular inspection of trees for early signs of the disease can help take timely action.

Tree Replacement: In cases where a tree is severely infected and poses a risk of spreading the disease or becoming hazardous, removal and replacement with a resistant species may be necessary.

Avoid Spreading: Be cautious when moving wood from infected trees, as this can spread the fungus to new areas.

Integrated Pest Management (IPM): Employ IPM strategies to manage insects and other pests that can stress trees and make them more susceptible to the disease.