Insect and Disease Management

Preventative spray or systemic trunk injection treatments can prevent emerald ash borer infestation. Once a serious infestation has begun it can be difficult to save your trees, so prevention and early treatment before signs of infestation appear is very important.

Hemlock woolly adelgids are spread from tree to tree by people, wind, birds and other animals starting in late winter/early spring. At this time, hundreds, if not thousands, of the speck-sized juvenile insects (crawlers) leave the woolly protection of the adult and migrate to other parts of the tree to settle and feed. Between March and August, the adelgids are most apt to spread from tree to tree, so care must be exercised around infested trees during this phase. Clipping infested branches between fall and early winter can control early infestations. For established infestations, timely and targeted spray treatments or systemic bark and root/soil treatments can effectively manage this insect. It is important to treat hemlocks early for the best outcome. 

Magnolia scale can be managed with carefully timed sprays of the juvenile stage of the insect. The juvenile stage occurs in the fall and early spring. The juvenille stage does not have the protective outer covering which the mature stage of the insect has.

The adult stage of the insect occurs later in spring and summer. It has an outer shell which protects it from sprays. On very small magnolias, the adult stage can be wiped off by hand.

Browntail moth caterpillars reside in a silken web at the tops of trees for approximately nine months of the year, including winter. Their webs are most easily identified in late winter/early spring when the silk web whitens and is reflected by the sun. Webs should be pruned out at this time of year and destroyed to prevent hatching.

Once temperatures warm in the spring and leaves begin developing, browntail caterpillars exit the webs and start feeding on new leaves. Foliar treatments can be applied at this time to effectively manage infestations. There are also systemic treatments which can be applied to other parts of the tree at this time or later in the summer/early fall.

Winter moths emerge from the soil in late fall/early winter, at which time they mate and deposit eggs on the bark of trees and shrubs. The moths then die, leaving only the eggs to overwinter on the plants. In early spring, tiny caterpillars hatch out of the eggs and wiggle onto and inside of the unopened plant buds to feed. The caterpillars also feed on the leaves once opened. In fall, heavy-weight sticky bands applied to tree trunks can help capture some ascending female moths before they deposit eggs, as the females are wingless and flightless. In spring, prior to egg hatch, a spray application of horticultural oil may prevent some eggs from hatching, especially on younger, smooth-barked trees where eggs are most exposed. Following egg hatch and leaf emergence, a targeted foliar insecticide application can manage infestations effectively. Other methods of treatment may also be effective in spring as well as late summer/early fall.

For mosquitoes, water management, traps and natural predators, such as bats, birds and dragonflies, can help reduce populations. Increasing sunlight and airflow through targeted pruning or vegetation removal can also be helpful. For ticks, creating a buffer of open space between outdoor activities near tall grass, dense shrubbery and trees, where deer, mice and other rodents which carry ticks are active, can help minimize contact.

A supplemental method of management is to treat larvae (mosquitoes), nymphs (ticks) and adults with an insecticide. Since ticks are most susceptible to treatment in the nymph stage, spring is an effective time for management. Depending on temperature and rainfall, mosquito treatment can start as early as April. Regular treatments throughout the summer may be needed for optimal control.

If you’re considering controlling mosquitoes or ticks with spray treatments, it is important to consult with a professional. Treatments must be used cautiously and limited to those with the proper certification and experience.

One way to prevent apple scab fungus is to plant varieties that are more resistant, such as Honeycrisp and Liberty. Raking leaves in the fall may reduce the spread of the fungus to other trees. However, leaf cleanup by itself is often insufficient to protect vulnerable trees. Timed foliar applications in spring are often the most effective way to ensure your trees are healthy and producing well.

Selecting disease-resistant varieties of evergreens is the best way to reduce the likelihood of infection from needlecast fungus. For existing trees, pruning to increase sunlight and airflow may help reduce infection. Timed foliar fungicide treatment in spring is often required to protect susceptible trees from initial or further infection.