Mature spongy moth caterpillar on a leaf. Photo: Bill McNee, Wisconsin DNR
Wisconsin Department of Natural Resources Forest Health staff are cautioning Wisconsin residents that the next two months could bring the worst spongy moth outbreak in more than a decade.
The caterpillars of this invasive insect prefer to feed on oak, birch, crabapple, aspen and willow leaves, but will also feed on many other tree and shrub species.
Southern Wisconsin and parts of the north are already in a high-population outbreak that is predicted to continue and spread. Populations have remained high due to a low incidence of caterpillar-killing diseases last summer. In addition, weather conditions in 2023 are favorable for the caterpillars and unfavorable for Entomophaga maimaiga, a fungus that kills spongy moth caterpillars.
Property owners are encouraged to examine their trees and take action. Specifically:
Three spongy moth egg masses on a branch in Walworth County. Photo Credit: Bill McNee, Wisconsin DNR
Now that spongy moth* (formerly known as gypsy moth) egg laying is complete for 2022, it’s a good time to look for and dispose of egg masses produced by adult moths over the past two months.
Spongy moth egg masses are tan-colored lumps about the size of a nickel or quarter, and are found on trees, buildings and other outdoor objects. They may also be found in protected places such as firewood piles and birdhouses. Newly produced egg masses will feel firm and appear darker in color than older egg masses, which appear faded, feel spongy and do not contain viable eggs. The current-year egg masses will not hatch until next spring.
In 2022, Wisconsin’s spongy moth population grew for a third consecutive summer due to favorable weather conditions and limited caterpillar mortality from diseases. The outbreak was most dramatic in opposite ends of the state. In southern and southeast Wisconsin, several thousand oak-dominated acres were heavily defoliated and very large numbers of property owner reports were received by DNR staff. In Bayfield County, about 80,000 acres of rural defoliation was reported from aspen-dominated forests. Smaller patches of defoliation were also reported from several other counties.Continue reading “Look For Spongy Moth Egg Masses – Larger Outbreak Possible in 2023” →
Tree damage from white pine weevil is noticeable across Wisconsin this time of year. White pine weevils attack several different Wisconsin species, including eastern white pine, jack pine and spruce.
Adult weevils lay their eggs on terminal leaders in the spring. After the eggs hatch, larvae bore into the terminal and begin feeding downwards just under the bark which can result in the killing of a 1 to 2-feet section of the terminal leader as they feed. Terminal leaders will often have a wilted or “shepherds crook” appearance, and they will turn rusty red to brown late in the fall season. These dead terminal leaders will often break off during the winter.
Dead terminal leader caused by a white pine weevil attack on a young white pine. Photo Credit: Wisconsin DNR
The oak slug sawfly (Caliroa quercuscoccineae), sometimes called the scarlet oak sawfly, has the appearance of a small, slimy slug. Its slime helps it stick to leaves it feeds on. The oak slug sawfly’s tiny larvae feed in groups on the undersides of oak leaves, scraping out the green material from between the veins of the leaves. The upper leaf surface is usually left intact, creating a “stained glass window” look. Oak slug sawfly has the ability to completely defoliate leaves before dropping to the ground to pupate.
Oak slug sawfly larvae cause defoliation on oak leaf after feeding. Photo Credit: Wisconsin DNR
Scattered damage to new red pine shoots has been observed across many counties this summer. With the intermittent rains during the summer, the first thought was that Diplodia shoot blight, a fungal disease, was causing the damage. Upon a closer look, some of the shoot mortality is caused by the red pine shoot moth. From a casual glance, these two problems will look the same, so you really need to take a closer look.
If Diplodia causes the shoot mortality, the shoot usually forms a shepherd’s crook. And, in time, you will find the fungal fruiting bodies on the needles, especially if you look under the needle sheath (covering) at the base of the needles.
Shepherd’s crook caused by Diplodia shoot blight. Photo Credit: Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org
White pine trees in many counties in northeast and northcentral Wisconsin have developed rusty-colored wilting needles on outer branch tips scattered throughout the tree’s crown. These dead branch tips are associated with the feeding by white pine bast scale. The scale is a tiny insect that inserts its straw-like mouthpart into the twig to suck sap from the outer layers of phloem called bast. Damage has been observed on trees over 20 feet tall this year.
Branch tips on this white pine indicate a problem with bast scale and the disease Caliciopsis. Photo Credit: Wisconsin DNR
Pear slug sawflies (Caliroa cerasi) feed by scraping off the upper layer of the leaf, leaving the veins and the lower leaf surface. Severe defoliation has been observed and reported recently on crabapple, apple, mountain ash and serviceberry in Oneida, Forest and Oconto counties. The first generation occurs earlier in the summer, so the larvae and defoliation seen now are due to the second generation of the insect, which is larger than the first generation.
Pear slug sawfly larvae feed by scraping off the upper layers of the leaf. Photo Credit: Wisconsin DNR