The Spongy Moths are here! I’ve had several reports from residents around the County. From the reports and inspections I’ve done, I’ve concluded that they like apple trees. Spongy moths, formerly known as Gypsy moths, are an invasive species that pose a significant threat to the forests of Northern Wisconsin. Their larvae, commonly referred to as caterpillars, are voracious feeders, capable of defoliating vast swathes of trees, which can lead to weakened trees, increased susceptibility to diseases, and, ultimately, tree mortality. Effective management and treatment strategies are crucial during the summer months of June, July, and August to mitigate the impact of these pests.
Spongy moths go through a complete metamorphosis: egg, larva, pupa, and adult. In Northern Wisconsin, the lifecycle is synchronized with the climatic conditions, making summer a critical period for intervention.
By June, spongy moth larvae are in their most destructive phase, feeding aggressively on the foliage of hardwood trees such as oak, birch, and aspen. In July, the larvae enter the pupal stage, during which they metamorphose into adults. In August, the adult moths emerge, mate, and lay eggs, setting the stage for the next generation.
Biological control involves the use of natural predators and pathogens to manage spongy moth populations. This method is environmentally friendly and sustainable in the long term. There is a naturally occurring bacterium, bacillus thuringiensis (Btk), that is a biological insecticide. When ingested by the larvae, it produces toxins that disrupt the caterpillars’ digestive system, leading to their death. Btk is most effective when applied in June when larvae are actively feeding. You can b uy a Btk spray on Amazon.
Another biological treatment is the Nucleopolyhedrosis Virus (NPV). This virus specifically targets spongy moth caterpillars. Infected larvae become lethargic and eventually die, releasing more viral particles into the environment to infect other larvae. You can purchase this virus/treatment at a few places in Wisconsin. I found Microbial Products in Hortonville, https://microbialwi.com.
Encouraging the presence of natural predators like birds, small mammals, and parasitoid wasps can help reduce spongy moth populations. Trichogramma wasps, for instance, lay their eggs inside spongy moth eggs, preventing them from hatching. I don’t know where you can get these wasps; probably just have to hope they show up.
Chemical insecticides can be effective but should be used judiciously to minimize environmental impact. Products containing diflubenzuron disrupt the molting process of caterpillars, preventing them from developing into adults. These should be applied in late June or early July before the larvae pupate.
Broad-Spectrum Insecticides are also effective. These insecticides can harm non-target species, though. They are usually reserved for severe infestations. Applications should be timed carefully, ideally in June when larvae are most vulnerable.
Physical methods of control include manual removal and destruction of egg masses and larvae. In August, after adult moths lay eggs, property owners can scrape off egg masses from tree trunks and branches and soak them in soapy water to kill the eggs.
Another method, is Burlap Banding. Wrapping tree trunks with burlap can trap caterpillars. Once trapped, the caterpillars can be collected and destroyed. This method is particularly useful in June and early July when larvae are actively moving. If they’re in the leaves, however, it’s too late.
Continuous monitoring of spongy moth populations is essential for timely and effective intervention.
Pheromone traps can attract and capture male moths, helping to monitor population levels and effectiveness of treatments. These traps are typically set up in late July and August. They can also be purchased on Amazon.
Engaging the public through education and participation in monitoring and control efforts can enhance the effectiveness of management programs. Residents can be trained to identify and report spongy moth infestations and participate in egg mass scraping and burlap banding. If you think you have an infestation, contact me and I’ll come out to check and offer ideas for management/treatment.
For more information contact Steve Kircher, County Conservationist-Land Information/GIS Director at 715-478-1387 or by e-mail at .