What’s Killing My Trees?

Many planters and drills were rolling this week in Northern Ohio. Some had to stop due to rain, others found conditions were not quite right. Soon, everyone will be moving again so watch out for the increased road activity during this busy planting season.

When the weather warms up, and there is some rain, usually mushrooms start popping up. Taking a walk this past weekend, I was looking at the trees. Many trees are very slow putting on leaves. Upon further inspection, many trees appear to be dead. Not small trees, fairly large trees, anywhere from 6 to 18-inch diameter trees. Upon inspection, 9 large trees were dead out of 12 trees in a fence row. Two weeks ago, after walking through a woods, there were dead trees down everywhere. Having walked that woods several times, these were mostly new logs, not all old logs. The question is: What is killing my trees?

The answer appears to be complicated. Maybe not just one factor, but several interacting factors. In the last several years, the weather has been both excessively dry and then excessively wet at times, often causing tree roots to get pruned back, which weakens the tree. Also, low freezing temperatures and quick changing weather conditions cause tree damage. Follow that up by high winds and many tree limbs, large branches, and even logs start coming down.

Also, when trees get weakened, insect damage increases. We also have numerous invasive insect species. The Emerald Ash Borer (EAB) killed many ash trees. However, that damage has been occurring for a number of years and many of those trees have been dead a long time already. EAB is a native of Asia and burrows under the bark, consuming the vascular system and ultimately it kills the tree. The Beech leaf tree disease is a microscopic nematode that affects mostly the American Beech tree. It weakens the tree and makes them susceptible to other diseases and insects. Northeastern Ohio has been decimated by this beech leaf tree disease.

Oak Wilt is a fungal disease that affects many oak trees by disrupting the vascular system leading to wilting and eventual death. Red oak, pin oak, black oak, and several other species can die within a few weeks of infection. Oaks in the white group (bur, swamp white, and white oak) are more tolerant. Thousand Canker Disease (TCD) is a relatively new disease that is spreading eastward, coming from Colorado. It is another fungus carried by the walnut twig beetle. Again, it affects the vascular system that carries water and nutrients throughout the tree. Walnut trees are most susceptible.

The Spotted Lanternfly (SLF) is another Asian invasive insect that infects and damages several trees and vines. Tree of heaven, grapes, and hops are most susceptible. It can also affect many different trees by causing them to leak sap from wounds and leave behind a sticky honeydew that leads to the growth of sooty mold. It generally weakens the hosts and opens up the plants to more diseases and insect damage.

The gypsy moth or spongy moth as it is now called is another invasive insect that causes considerable damage to many tree species. The caterpillar or larval stage feeds heavily on leaves and weakens the tree by defoliation. The spongy moth feeds on many hardwood trees including oaks, apple, sweetgum, basswood, gray and white birch, willow, hawthorn, and other tree species.

Another issue are agricultural herbicides like glyphosate, dicamba, and 2-4D. With new GMO corn and soybean varieties which are genetically resistant to these chemicals, they may cause significant drift damage to non-targeted plants including trees and shrubs. Glyphosate (Roundup) can drift up to 4 miles and is a chelator of many micro-nutrients. It tends to weaken trees and shrubs so disease and insect pests can increase tree damage. Dicamba (Banvel, Oracle, Diablo, Dianat) tree injury causes tree leaves to cup, twist, or pucker and may cause limb dieback or even tree mortality. Dicamba may cause leaves to yellow or discolor, can be taken up by roots, and is a hormone disrupter in the plant. It generally weakens trees, reduces growth, and with repeated exposure, tree mortality is possible. Oak trees are especially susceptible to dicamba drift. The damage from 2-4D drift is similar to dicamba with cupped, twisted, and discolored tree leaves.

In summary, there are many factors which are causing trees to weaken, grow slowly or even die. Weather conditions are a major factor along with invasive insect and disease pests. If you add in some chemical drift, trees and shrubs have many issues to deal with to survive.