![]() Currently recognized strains of Xylella fastidiosa and a partial list of the plants they infect. A partial list of susceptible plants is provided in Table 1. Other important diseases caused by Xylella fastidiosa include Pierce’s disease of grapes, citrus variegated chlorosis, phony peach disease, and plum leaf scald. The pecan kernels that are produced will be smaller than normal. Infected pecans show typical leaf scorch symptoms and will not produce as many nuts. The twigs and stems of young infected blueberry plants may look yellow, a symptom that is most noticeable after the scorched leaves have fallen. In addition to ornamental plants, bacterial leaf scorch also affects rabbiteye and southern highbush blueberry varieties and pecans. Bacterial leaf scorch also may only affect one branch or a part of the plant, whereas drought stress will affect the entire plant. In the case of drought stress, the edge of each leaf will be evenly brown, and symptoms will appear first on the leaves at the tips of branches (the youngest leaves). Scorch symptoms begin on the oldest leaves on the branch young leaves at the tips of branches may remain green. For plants infected with Xylella, the pattern of browning at the edge of the leaf is usually irregular. Laboratory testing is the only way to confirm that a plant has bacterial leaf scorch, but there are some clues to help tell the difference between drought stress and the disease in the landscape. Note the yellow halo separating the scorched tissue from the green tissue. Bacterial leaf scorch on winged elm (Ulmus alata). Hot, dry weather increases the severity of symptoms. Usually, leaf symptoms first appear in late spring and early summer. Leaves fall from the plant well before normal fall leaf drop. The edges of leaves become brown or “scorched,” and often there is an area of yellow leaf tissue between the scorched leaf edge and the healthy green leaf tissue near the center of the leaf (Figure 1). ![]() When the water-conducting tissue of the plant becomes clogged with bacteria, not enough water reaches the leaves. Symptoms of bacterial leaf scorch look a bit like drought stress. The disease is caused by Xylella fastidiosa, a bacterium that gets its name because it is limited within the plant to the water-conducting tissue (xylem) and because it has very specific nutritional needs (fastidious), making it very difficult to grow outside the plant. Bacterial leaf scorch is a disease of shade trees, ornamental plants, and economically important food crops such as peaches, pecans, blueberries, and citrus.
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