Common American Elm Tree Diseases:
How to Identify and Treat

American Elm trees are beloved for their elegant appearance and wide canopy that provides ample shade. However, these majestic trees are susceptible to various diseases that can affect their health and longevity. Identifying these diseases early on is crucial in order to implement proper treatment strategies to save the tree. In this article, we will discuss some of the most common American Elm tree diseases, how to identify them, and the best ways to treat them.

Dutch Elm Disease (DED)

Dutch Elm Disease is one of the most devastating diseases that affects American Elm trees. It is caused by a fungus called Ophiostoma novo-ulmi, which is spread by elm bark beetles. The disease blocks the tree’s vascular system, leading to wilting, yellowing of leaves, and eventually death.

Identification:

• Wilting and drooping of leaves on one or more branches.
• Yellowing or browning of leaves, starting from the top of the tree.
• Brown streaks in the sapwood when a branch is cut.
• Presence of elm bark beetles on the tree.

Treatment:

• Pruning: Remove and destroy infected branches promptly to prevent the spread of the disease.
• Fungicide Treatment: Consult with a professional arborist for fungicide treatments to protect healthy trees from infection.
• Plant Resistant Varieties: Consider planting DED-resistant elm varieties to prevent future infections.

Elm Yellows

Elm Yellows is a phytoplasma disease that affects American Elm trees, causing yellowing and stunting of foliage, premature leaf drop, and eventually death.

Identification:

• Yellowing and curling of leaves.
• Stunted growth and overall decline in tree health.
• Presence of witches’ brooms (abnormal growth clusters) in the canopy.

Treatment:

• Pruning: Remove infected branches to improve air circulation and reduce stress on the tree.
• Insect Control: Manage insect vectors that spread the disease, such as leafhoppers.
• Fertilization: Provide balanced fertilization to boost tree health and immune system.

Anthracnose

Anthracnose is a fungal disease that affects many tree species, including American Elms. It thrives in wet conditions and causes leaf spotting, defoliation, and branch dieback.

Identification:

• Brown or black spots on leaves with irregular margins.
• Twisted or distorted growth of new shoots.
• Premature defoliation during the growing season.

Treatment:

• Pruning: Remove and destroy infected plant material to prevent further spreading.
• Fungicide Application: Apply fungicides in early spring before symptoms appear as a preventive measure.
• Improving Air Circulation: Ensure proper spacing between trees to promote air circulation and reduce humidity.

Elm Leaf Beetle

Elm Leaf Beetle is an insect pest that feeds on American Elm tree foliage, causing skeletonization of leaves and weakening the tree’s overall health.

Identification:

• Skeletonized leaves with only veins remaining intact.
• Larvae feeding on the underside of leaves.
• Adult beetles emerging in spring and laying eggs on twigs.

Treatment:

• Biological Control: Introduce natural predators like ladybugs or parasitic wasps to control beetle populations.
• Insecticidal Soap: Spray affected foliage with insecticidal soap to kill larvae and adults.
• Tree Banding: Wrap sticky bands around tree trunks to trap crawling larvae before they reach foliage.

Conclusion

Maintaining the health of American Elm trees requires vigilance in identifying and treating common diseases promptly. Regular inspections, proper cultural practices, and timely interventions can help protect these iconic trees from succumbing to deadly pathogens. If you suspect your American Elm tree is affected by any of the diseases mentioned above, it is advisable to seek advice from a certified arborist for accurate diagnosis and appropriate treatment recommendations. By taking proactive measures, you can ensure the longevity and vitality of your American Elm trees for generations to come.