From the Viette's Views Gardening Blog
It’s always the last Friday in April although some states recognize a different State Arbor Day that corresponds better with planting times in their state. Since Arbor Day was founded in 1872, it has been customary to plant a tree in observance of the holiday and on that first Arbor Day, it is estimated that about one million trees were planted.
As you celebrate Arbor Day this year, keep in mind that as important as it is to plant new trees, it is equally important to care for and protect the trees that are already growing in your landscape.
Damage to mature trees due to insects and diseases (many introduced from other countries) can be devastating to your landscape as well as the surrounding areas and adjoining forests. Diseases such as the Chestnut blight and Dutch elm disease and exotic insects like the emerald ash borer and the Asian long-horned beetle have killed tens of millions of trees across the U.S.
The chestnut blight, caused by a fungus (Cryphonectria parasitica), was introduced to North America from Asia in the early 1900’s either on infected lumber or through diseased trees. Within 40 years of its introduction, virtually all the chestnut trees in North America were wiped out. Although mature American chestnut trees have disappeared from our forests, small trees often grow from stump sprouts since the blight doesn’t kill the roots. Unfortunately, these small trees rarely grow to reproductive age before they are attacked and killed by the fungus. Such a sad ending for these once majestic trees which often reached 200 feet tall and 14 feet across!
There is no cure for this disease but much work has been done to genetically engineer a disease resistant American chestnut using genetic material from a few stump sprouts that managed to produce seeds and a bit of DNA (as little as 3%) from Asian species that show resistance to the blight.
The American Chestnut Foundation is at the forefront of this research with a mission …
" …to restore the American chestnut tree to our eastern woodlands to benefit our environment, our wildlife, and our society. The American Chestnut Foundation is restoring a species – and in the process, creating a template for restoration of other tree and plant species.”
Another pest that is doing its best to wipe out whole a species of trees is the hemlock woolly adelgid (Adelges tsugae). This past Sunday on a wonderful but rainy walk in the George Washington National Forest, Eric and I saw evidence of this destructive pest on a young hemlock. The hemlock woolly adelgid was also an accidental introduction from Asia and is devastating populations of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) throughout eastern North America. The insect damages the trees by feeding at the base of the needles causing them to desiccate and eventually drop off. Heavy infestations have been known to kill trees in as little as four years but healthy trees can sometimes survive an attack for a longer period of time. Luckily, there are products that the homeowner can use to help control hemlock woolly adelgids but sadly in our hemlock forests, these pests are causing the destruction of large numbers of these beautiful trees.
As they have with the American chestnut, researchers have developed an adelgid-resistant hybrid by crossing the Carolina hemlock with an Asian hemlock which is resistant. While this is great progress – it does nothing to save the trees that are already infected!
Another group of insects that causes widespread damage to established trees is the wood-boring insects including the emerald ash borer, the Asian long-horned beetle (both introduced from Asia), and a wide variety of the bark beetles.
The emerald ash borer, first reported in Michigan in 2002, has already killed millions of ash trees and is a potential threat to all the ash trees in North America.
The Asian long-horned beetle is one of the most destructive of the wood borers because it is not selective and attacks a wide variety of hardwood trees.
Bark beetles, like the spruce beetle, the mountain pine beetle, and the southern pine beetle, have killed millions of conifers in North American forests especially during severe outbreaks.
In Alaska, the spruce beetle has killed entire forests of Sitka Spruce. Although bark beetles generally attack trees that are weak, dying, or already dead, the species listed above are particularly destructive because they will attack live, seemingly healthy trees.
For the homeowner, there are products that can be used to help control some of these pests. Horticultural oils can help control the woolly adelgid if they are sprayed at the correct times.
Some systemic insecticides may help control adelgids, emerald ash borers, Asian long-horned beetles, and pine borers. Bayer Advanced 12 Month Tree & Shrub Protect & Feed II and Bonide Annual Tree & Shrub Insect Control are products that can be mixed and poured at the base of the tree according to the label directions. These products are not available in all states.
Always read and follow the label directions when using pesticides.
On this Arbor Day, The Nature Conservancy reminds us of some important tips to help protect our trees.
So make a pledge this Arbor Day to pay attention to your existing trees and strive to keep them strong and healthy!