Borers are the larvae of beetles or moths. Many kinds of borers attack maples. Throughout the summer, females lay eggs in bark crevices. The larvae feed by burrowing into the tree and tunneling through the bark, sapwood, or heartwood. This stops the flow of nutrients and water in that area by cutting the conducting vessels; branch and twig dieback result. Sap flow acts as a defense against borers. When the borer burrows into the wood, tree sap fills the hole and drowns the insect. Young or weakened trees are attractive to borers and may not produce enough sap to drown all the borers that invade them.
Cut out and destroy all dead and dying branches, and remove young trees that are severely infested. Maintain plant health and vigor by watering and fertilizing regularly.
Many different fungi cause leaf spots; some common leaf spot diseases are tar spot and phyllosticta spot. Leaf spots are unsightly but rarely harm the tree. The fungi are spread by wind and splashing water. Spots develop where the fungi enter the tissue. If wet or humid weather persists, the infection spreads through the tissue and blotches form. The fungi survive the winter on twigs and fallen leaves. Most leaf spot organisms do their greatest damage in mild weather (between 50° and 85°F).
Fungal leaf spots on maples are usually not harmful and do not require control measures. To reduce recurrence the following year, rake up and destroy the leaves in the fall.
This plant disease is caused by two related fungi (Discula spp. and Kabatiella apocryta) that spend the winter on fallen leaves or in sunken cankers on twigs in the tree. During cool, rainy weather, spores are blown and splashed onto newly expanding and young leaves. Dead spots develop on the leaf where the fungus enters the tissue. The spots expand, and the fungus can kill the leaf in rainy seasons, causing premature defoliation. The tree will grow new leaves if defoliation takes place in spring or early summer. When the tree is severely affected for successive years, the fungus will enter and kill branches.
Rake old leaves and prune out dead twigs below the canker on the bark. This reduces the amount of disease the following year. Apply a fungicide labeled for this disease, following label directions.
Caulocampus acericaulis This insect is the larva of a sawfly, a non-stinging wasp. Adults lay single eggs on the leaf stem (the petiole) in mid-spring. The larva that hatches bores into the petiole and feeds there for 20 to 30 days. The larva is up to 1/3 inch long and cream-colored with a brown head. The boring weakens the petiole, which turns dark and shrivels, then breaks. The larva feeds within the portion of the stem still attached to the tree until it falls 10 days later. The larva emerges from the stem and digs into the ground, where it spends the winter, to pupate and emerge as an adult wasp in the spring. Maple petiole borers were introduced to New England from Europe and have since spread to the Great Lakes and Upper Midwest. They attack all species of maple, but prefer sugar maples. Usually they are controlled by natural enemies, but sporadic outbreaks occur every few years. They do little long-term damage to the tree.
The borers do little damage, so it is best to ignore the problem. Most years, the damage is not noticeable.
Leaf scorch is caused by excessive loss of moisture from the leaves due to evaporation. In hot weather, water evaporates rapidly from the leaves. If the roots can''t absorb and convey water fast enough to replenish this loss, the leaves turn brown and wither. This usually occurs in dry soil, but leaves can also scorch when the soil is moist. Drying winds, severed roots, limited soil area, or low temperatures can also cause scorch.
To prevent further scorch, deeply water trees during periods of hot weather to wet down the entire root space. Water newly transplanted trees when the soil is dry. Scorch occurring on trees in moist soil cannot be controlled. Plant trees adapted to your climate.
This wilt disease affects many ornamental trees and shrubs. It is caused by a soil-inhabiting fungus (Verticillium) that persists indefinitely on plant debris or in the soil. The disease is spread by contaminated seeds, plants, soil, equipment, and groundwater. The fungus enters the tree through the roots and spreads up into the branches through the water-conducting vessels in the trunk. The vessels become discolored and plugged. This plugging cuts off the flow of water and nutrients to the branches, causing leaf discoloration and wilting.
Fertilize to keep the tree vigorous. Remove all deadwood. Do not remove branches on which leaves have recently wilted. These branches may produce new leaves in 3 to 4 weeks or the following spring. Remove dead trees. If replanting in the same area, plant resistant trees and shrubs.