![]() Mulching leaves will destroy many of the spots before they mature, but the mulch pile should be covered or turned before new leaves begin to emerge in the spring.Īpplications of fungicides are possible when high levels of infection become unacceptable, but control of tar spot is challenging, especially on mature maples. Neighbors should also rake and destroy infected leaves to be effective. This will reduce the number of overwintering “spots” (containing the fungal reproductive structures) that can infect new leaves the following spring. ![]() Since tar spot fungi overwinter in fallen leaves, the most effective management technique is to rake and destroy leaves in the fall. Heavy infections can cause premature leaf drop – a circumstance that causes great consternation to homeowners because lawns are littered and must be raked before autumn typically arrives. This disease is usually a cosmetic problem and does not affect the long-term health of the tree. Silver maple leaf infected with tar spot. Wilson, MSUE.Ĭurrent symptoms on Norway maple. (This is the time when homeowners become rather alarmed.) Symptoms tend to be more common on trees growing in moist, sheltered locations.Įarly symptoms on Norway maple. The black spots continue to grow in diameter and thickness to the point where it looks like someone splashed tar on the leaves. Small, black, tar-like raised structures form on the upper surface within these yellow spots. The spots enlarge and color intensifies as summer progresses. The first tar spot symptoms usually show up in early summer as small (less than 1/8 inch diameter), light-green to yellowish-green spots. ![]() It’s also one of the least damaging ailments on its host. Tar spot is one of the most readily visible and easiest maple diseases to diagnose. The disease is caused by several fungi in the genus Rhytisma and infects silver, sugar, red and Norway maple as well as their relative, box elder. After teasing out additional information from callers, most folks are seeing symptoms of a fungal disease known as tar spot. Like Norway maple, flowers are yellowish-green, but they tend to appear in late April to May, and each hanging flower cluster is 6-12cm long.Homeowners with maple trees are calling the Michigan State University Extension Lawn and Garden Hotline concerned about numerous spots appearing on the leaves. Opposing buds are green, and the flowers appear at the same time as the foliage. Sycamore has large leaves with five coarsely-toothed lobes.Fruits are paired and the wings spread on the horizontal or at a wide angle Flowers appear in April before the leaves, and the yellowish-green flowers grow in erect clusters. The opposing buds (characteristic of all acers) are deep red. Norway maple has large leaves with five to seven lobes.Other ways to distinguish between the two species (depending on the time of year) include comparing buds, flowers, leaves and samaras. Unlike sycamore, Norway maple exudes a milky sap when the leaf stalks are broken. Sycamores can reach 35m in height, taller than Norway maples, but their autumn colour is less spectacular. Acer platanoides can be confused with sycamore ( Acer pseudoplatanus), another naturalised European species introduced into Britain centuries ago, and widely planted from the 1700s. ![]()
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