- 1). Watch for a yellowing of the foliage; this may be a sign of chlorosis. The lack of needed nutrients in the surrounding ground -- including zinc, iron and manganese -- will eventually cause the maple's leaves to yellow, with only the veins of the leaf remaining green. Chlorosis may affect the maple over many years, with new leaf growth showing obvious yellowing.
- 2). Inspect sugar, Norway and red maples for the disease known as maple decline by looking for reduced growth of new twigs, sparse foliage, early onset of fall color change in the leaves and dead branches in the top of the tree. Maple decline, brought on by insects devouring foliage over a period of years, also results in dead or brittle roots on the tree.
- 3). Examine a maple for signs of anthracnose, a fungal disease that causes leaf buds to die and early loss of leaves at the beginning of the growing season. Anthracnose makes a maple drop its leaves much earlier than usual in the fall. Watch for purplish-brown areas on the leaf to develop along veins. Inspect the leaf for brown spots between or near veins, with some going all the way to the edge of the leaf. Anthracnose typically strikes a maple tree during an exceptionally cool, wet spring as the leaf buds open, according to Tree Help.
- 4). Recognize verticillium wilt by the way this fungal disease kills one or multiple branches on the tree. The leaves on a maple infected by verticillium wilt will wither prematurely, often before July is over, with many displaying symptoms such as brown edges. Norway maples, as well as sugar, red, silver and Japanese maples are susceptible to verticillium wilt.
- 5). Look for small spots of pale yellow to appear on maple leaves by the middle of June as an indicator of tar spot. The fungal malady is not serious, but does affect the character and appearance of your maples. The 1/8-inch yellow areas over time get bigger and darker, growing to an inch in diameter and resembling a drop of black tar. One form of tar spot, common on Norway and striped maples, results in as many as 50 small spots on each leaf, according to the Cornell University Plant Disease Diagnostic Clinic.
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