Xylella And Oaks: What Causes Oak Bacterial Leaf Scorch

Xylella And Oaks: What Causes Oak Bacterial Leaf Scorch

By: Darcy Larum, Landscape Designer

By Darcy Larum, Landscape Designer

Plant diseases in trees can be tricky things. In many cases, symptoms can go unnoticed for years, then seem to cause sudden death. In other cases, the disease may show obvious symptoms on certain plants in the area but then can affect other plants in the same location in completely different ways. Xylella leaf scorch on oaks is one of these confusing, difficult to diagnose diseases. What is xylella leaf scorch? Continue reading to learn more about oak bacterial leaf scorch.

What is Xylella?

Xylella leaf scorch is a bacterial disease caused by the pathogen Xylella fastidiosa. This bacteria is believed to spread by insect vectors, such as leafhoppers. It can also be spread from grafting with infected plant tissues or tools. Xylella fastidiosa can infect hundreds of host plants, including:

In different species, it causes different symptoms, earning it different common names.

When xylella infects oak trees, for instance, it is called oak bacterial leaf scorch because the disease causes the leaves to look as if they’ve been burned or scorched. Xylella infects the vascular system of its oak host plants, inhibiting the flow of xylem and causing the foliage to dry out and decline.

Olive green to brown colored necrotic patches will first form on the tips and margins of oak leaves. The spots may have light green to reddish brown halos encircling them. The foliage will turn brown, dry out, look crunchy and burnt, and drop prematurely.

Treating an Oak Tree with Xylella Leaf Scorch

Symptoms of xylella leaf scorch on oak trees can appear on just one limb of the tree or be present throughout the canopy. Excessive water sprouts or weepy black lesions may also form on infected limbs.

Oak bacterial leaf scorch can kill a healthy tree in just five years. Red and black oaks are specifically at risk. In its advanced stages, oak trees with xylella leaf scorch will decline in vigor, develop stunted foliage and limbs or have delayed bud break in the spring. Infected trees are usually just removed because they look so terrible.

Oak trees with xylella leaf scorch have been found throughout the eastern United States, in Taiwan, Italy, France and other European countries. At this point, there is no cure for the worrisome disease. Annual treatments with the antibiotic Tetracycline alleviate the symptoms and slows down progress of the disease, but it does not cure it. However, the United Kingdom has launched an extensive research project to study xylella and oaks infected by it to protect their nation’s beloved oak trees.

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