Michigan residents in northern parts of the state are noticing loss of leaves on oak, aspen and maple trees. The prime culprit contributing to this defoliation is the gypsy moth. Department of Natural Resources forest health officials report that, while the most obvious defoliation is currently heaviest in Crawford, Oscoda, Otsego and Montmorency counties, it is likely that gypsy moth caterpillars are causing similar problems on a local scale in other areas of the Lower Peninsula.
“Gypsy moth caterpillars are nothing new to our state,” said DNR forest health specialist Dr. Robert Heyd. “They’re a recurring challenge. We most often see defoliation in the season following a particularly drought-heavy year like we experienced in 2012. Many forest pests tend to target trees that are weakened – perhaps from drought – or otherwise not in optimum health. The number one thing people can do to reduce the effects of pests like gypsy moth is promoting tree health.”
Regular watering and avoiding damage to roots and bark go a long way in helping trees fend off the effects of defoliation. Likewise, periodically removing dead and dying trees in woodlots keeps remaining trees growing strong.
Heyd explained that gypsy moth populations surged across the state during the 1980s and 1990s, defoliating many woodland areas. At that time, the moth was fairly new to the state and, like any introduced species, its population grew rapidly without natural control from parasites, pathogens and predators.
During this period, the Michigan Department of Agriculture and Rural Development worked with local communities to conduct aerial spraying to reduce gypsy moth nuisance in areas with high caterpillar numbers. When done properly, using biological insecticides, aerial treatment can help make life more tolerable during outbreaks, without affecting the natural enemies that eventually bring gypsy moth populations under control.
While these spray programs are no longer conducted by the state, natural enemies of the gypsy moth are now well-established across Michigan and are actively helping to reduce populations. Two pathogens in particular – the nucleopolyhedrosis virus (NPV) and a fungus, Entomophaga maimaiga – are killing gypsy moth caterpillars in large numbers across much of the Lower Peninsula. Wet spring weather in many areas has given these organisms the upper hand, helping them to develop and spread quickly.
Surviving gypsy moth caterpillars are currently spinning cocoons to transform into moths later in July. With the caterpillar stage nearing an end in most areas, it’s too late for spraying to help.
The good news is that defoliated trees are already beginning to develop new leaves to replace those that were eaten. And even heavily defoliated trees will recover without serious long-term effects.
Heyd said gypsy moths rarely kill trees in Michigan.
“Historically, only trees already suffering from problems like drought, old age or root damage are at risk,” he added.
To learn more about gypsy moth caterpillars, visit the MSU Extension website at http://msue.anr.msu.edu/topic/info/pest_management. More detailed information is also available in a MSUE bulletin that covers the origins, lifecycle and other facts about the gypsy moth caterpillar.
