Winter Moths Pose Real Danger to Your Trees' Buds

(Editor's note: The following information was submitted by Mahoney's SafeLawns and Landscaping.)

Tree buds are a welcome sign of spring. Unfortunately, the winter moth is due to return within the next several weeks and attack those beloved buds.

If not treated properly, emerging leaves could be riddled with holes, and complete defoliation may ultimately kill the tree in as little as four-years. A variety of treatments are available that should be applied now to protect, not only the beautiful foliage, but the health of the trees.

“Winter moth is very destructive to a wide range of deciduous plants such as apple, cherry, blueberry, maple, oak, linden and ash,” says Kristina MacPherson, Manager for . “In Massachusetts, the Eastern part of the state typically sees the most damage, making preventative measures important to saving our trees.” 

Many outbreaks popped-up last spring, causing concern for this spring. Additionally, the high amount of winter moths we saw this winter is an early warning sign that outbreaks may be high.

 When temperatures begin to average 55°F, as we should be experiencing within the next few weeks, the winter moth eggs begin to hatch. The newly hatched caterpillars, resembling an inch worm with a white “racing stripe” down the side, wiggle their way under the scales of flower and leaf buds to feed on the unopened bud.

As the caterpillars grow, they continue to feed on unfolding leaves and are capable of defoliation on a large scale.  If spring flowering is delayed, the problem is further intensified as caterpillars continue to feed on closed buds. In fruit trees, such as apple or blueberry, this may lead to a loss of fruiting.

Fortunately, treatments as outlined below are environmentally friendly if handled and applied properly, and very effective against the winter moth.

As a first level of defense, MacPherson recommends spraying trees now while they are dormant (no leaves out) with a horticultural oil, such as Bonide All Seasons Horticultural Oil, to smother the eggs. Spray should be applied when temperatures are above freezing for 48 hours, so as not damage the plants. Cover as much bark and stems as can safely be reached.

This method will dramatically lower populations; however, additional treatments may be needed “as some eggs may be protected by bark or lichens on the tree.”

As leaves unfold, caterpillars will appear to swing from the trees on silky strands spreading to neighboring trees. At this time a foliar insecticide spray may be applied.

“We recommend spraying trees with a product containing spinosad, such as Bonide’s Captain Jack’s Dead Bug Brew,” says MacPherson. “Spinosad is a natural bacterium that targets caterpillars and similar insects.  Once ingested, the caterpillars will stop feeding immediately and die within two-to-three days.” 

If trees are sprayed as the leaves are unfolding, MacPherson advises additional applications to protect the untreated foliage.

Unfortunately for the typical homeowner, many trees are far too large to treat on their own. Many companies, such as , have now emerged that offer spraying services capable of reaching the tops of large trees.

According to MacPherson, treatment is best applied now to protect healthy plants from defoliation. For more information you can visit www.MahoneysSafeLawns.com or call (781) 305-5555.

MacPherson notes that with any treatments, always read and follow label instructions. Additionally, when spraying fruit trees, care should be taken to protect foraging bees by spraying early in the morning or late in the afternoon when the bees are less active.