The browning of plant tissues, including leaf margins and tips is a condition known as leaf scorch, a common condition caused by various factors. In hot and arid regions, this is mainly caused by excessive heat during droughts. Other possible causes which also lead to leaf scorch are improper plant care, soil compaction, transplant shock, nutrient deficiency or over-fertilization. Exposure to bacterium carrying insects, herbicides or salt toxicity may also lead to symptoms of leaf scorch.
Leaf Scorch Caused by Environmental Conditions
Leaf scorch caused by weather conditions can affect almost any plant. High temperatures, dry winds, and low soil moisture are favourable. When water evaporates from leaf surfaces, plant roots are unable to compensate for the transpiration loss. Leaf tissue then dies as a direct result. Young trees that are stressed by insect infestations, diseases, or other factors are more susceptible than those growing vigorously and in good condition.
Japanese maples, Norway and sugar maples, beech, ash, oak, linden, birch, alpine currant, horse chestnut, white pine, rhododendron, viburnum, and flowering dogwood tree and shrub plants are particularly prone to leaf scorch. Understanding and meeting the specific needs of plants and maintaining proper soil conditions, including proper watering practices, are all vital for preventing leaf scorch effectively.
Leaf Scorch Caused by Bacteria
Bacterial leaf scorch is a chronic, eventually fatal disease that has devastated many shade trees in landscapes and street plantings. Bacterial leaf scorch (BLS) is a systemic disease caused by the bacterium Xylella fastidiosa, which invades the water and nutrient-conducting tissues of trees.
Bacterial Leaf Scorch of Shade Trees
Bacterial leaf scorch is most common with pin, red, shingle, bur, and white oaks, but can also affect elm, sycamore, mulberry, sweetgum, sugar maple, and red maple. Tissue-feeding leafhoppers and spittlebugs spread the bacterium from tree to tree. Bacterial leaf scorch can easily be mistaken with symptoms of drought and heat stress and the only way to confirm its presence is through laboratory analysis.
The best time to test for the presence of this disease is in late summer or early fall when the bacteria count is at its highest. Transmission between trees through root grafts has also been reported.
Infected leafhoppers and spittlebugs feed on the succulent, terminal shoots of susceptible host trees, transmitting the bacteria. Water transporting tissue vessels become clogged with bacteria as they travel within, multiplying and infecting other parts of the tree. There are no viable control options for the insects.
The cold-sensitive bacteria overwinters in protected areas within the tree, and populations begin to climb again as the next growing season progresses.
Leaf Scorch Management
Maintaining the vigor of plants by keeping susceptible specimen healthy and thriving can help them resist infection and survive longer once they are infected. Branches that have died due to bacterial leaf scorch should be removed. Infected trees in a severe state of decline should also be removed. Disinfect pruning tools with a 10% bleach solution between pruning cuts.
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