Typically, around this time of year I will get a few phone calls regarding Elm Trees. Most folks believe their Elm tree is dying. As much as I would actually prefer our Siberian elms to go away, as they do offer plenty of shade, they are not dying! It pretty hard to really kill one of these trees, and you will typically find them growing just about anywhere! But back to why they appear to be dying this time of year. The culprit is the Elm Leaf Beetle.
The mature elm leaf beetle are approximately 1/5-1/4 inches in length and have a yellow to dull green appearance with a black strip on each side of the wing cover and one in the middle that extend the length of the body. In addition, there are two black spots on both sides of the thorax (middle portion), and two distinct short black lines just behind the thorax.
These insects feed on the leaves. Adults feed on the entire leaf, while larva feed on the underside of the leaving causing the leaves to appear brown to our eyes as the eat the green out of the leaf. Upon closer inspection, the leaves have a skeletonized brown appearance. Usually it is the second generation feeding where we can begin to notice the damage, unless the tree is heavily infested in the spring.
In most cases, the elm trees have plenty of time to photosynthesize over the summer and can afford to lose their leaves a little earlier than we would prefer. In the spring, the tree leaf out again and the cycle will continue.
In severe cases, or for those that want green leaves to the end of the growing season, insecticides can be applied. Systemic insecticides can be applied to the soil where they are absorbed by the roots and translocated to the leaves that will be fed upon by elm leaf beetle larvae and adults. Applications should be made in early spring before new growth emerges. Keep soil moist to increase absorption of the systemic insecticide by the root system, and promote translocation throughout the tree. Always read product labels carefully to determine those insecticides that can be used against elm leaf beetles.
