This summer the Extension Master Gardener hot line has received several calls from homeowners and landscapers asking why their tree suddenly died. The typical scenario sounds something like this, “I went on vacation for a week and when I came home my tree was dead. It was perfectly healthy before I left.” The phone calls have been pretty much the same, with the only difference being the type of tree that died. Once a tree has died we can only speculate the reasons for its death. The way a tree dies, gradually versus all of a sudden, can help narrow down the possibilities.
Tree life span varies greatly by species. Typically slow growing trees live longer than fast growing ones. It is good to have an idea of a tree’s life span when choosing a tree. But don’t let a short life span stop you from selecting a tree that may bring you 20-25 years of pleasure. When a tree dies always find out what species it was so that natural causes can be ruled out. A few questions to ask, include:
Have you sprayed a pesticide (herbicide) recently? Herbicides used to target broadleaf weeds sometimes come into contact with non-targeted plants. When the wind is blowing, pesticides can travel great distances and harm other plants. Plants typically exhibit symptoms like curled up leaves and / or bleached out color. Large trees normally will recover.
What kind of environment was the tree planted in? Trees can’t tell us with words when they are not happy where they have been planted. That’s why it’s a good idea to do an analysis of the existing environmental conditions before selecting a tree. Are the soils typically wet or dry? Is it sunny or shady? Is there good air movement? A tree planted in the wrong place will suffer quietly for a long time. Symptoms often include: wilting of leaves if the soil is too wet, leaf desiccation if the soils are too dry, powdery mildew on the leaves if the tree prefers sun and is planted in the shade, and a greater susceptibility to insect and disease due to stress.
Have you looked at the roots? Root rot (Phytophthora cinnamomi) is common in heavy clay soils that tend to hold moisture. Most trees prefer moist well drained soils. Trees sitting in water can also die from lack of oxygen. Symptoms of root rot include slow dieback of limbs, chlorosis of the leaves and defoliation. The leaves initially wilt and then turn brown.
Have you done a soil test recently? Soil testing is free, and boxes are available at county extension offices across the state. Testing is done by the NC Department of Agriculture Agronomic Division. Soil tests will indicate whether or not there are nutrient deficiencies in the soil, the soil pH is high, low, or just right, or whether there are high salts in the soil. Excessive fertilizer in the soil causes reverse osmosis in the roots of a plant. This means instead of the roots absorbing water, the soil is pulling the water out of the tree causing fertilizer burn. Symptoms include wilting, leaf desiccation and death. Nutrient deficiencies can be seen in the leaves in some form of chlorosis. This can easily be corrected once the nutrient deficiency is identified.
Are there symptoms on the bark? Voles, deer, beaver, borer insects and weed wackers are all major pests to trees. Voles feed on the roots of plants and are known to eat the lower bark of trees. Deer when desperate will eat anything, even bark, and also tear off tree bark when rutting. Borer insects are typically attracted to very specific tree species. They will enter a tree near the base at the soil line. Symptoms of a borer insect include oozing gummy sap at the entrance hole. Weed wacker damage wounds the tree making it more susceptible to insects and disease. In some cases, a weed wacker has girdled the tree preventing nutrients from moving up and down the trunk and killing the tree.
How much mulch? Keep mulch 4-6 inches away from the trunk of the tree to prevent rotting. Over mulching is a case when “too much of a good thing can kill you.” The recommended amount of mulch for reducing weeds and retaining moisture is 2-4 inches. Too much mulch can affect the amount of oxygen available to the tree. The roots in an effort to find oxygen will begin to grow into the mulch instead of the soil. This stresses a tree and can eventually lead to its demise.
How do the leaves look? Many trees exhibit symptoms of stress on their leaves. When it’s hot they may wilt, in a drought they may defoliate and induce early hibernation, if the species is susceptible to various diseases many of the symptoms appear on the leaves. Some diseases primarily impact the trees aesthetic appearance while others cause serious damage leading to death. Insect pests can also impact the aesthetic appearance but don’t always merit control since the damage they cause doesn’t always impact the tree long term.
Most tree symptons appear gradually, so when a caller says their healthy tree “just died over night or within a week”, that symptom of speedy demise suggests a few possible causes: Armillaria Root Rot (a fungal disease that infects and kills woody plants that are weak) or drought. While we have had a fairly rainy season this year, it surprises people when I tell them their healthy tree probably died from the drought. Trees will struggle for years without showing symptoms of stress. A drought can inhibit a tree’s ability to expand its root system and develop. When rain finally comes a young tree may not have developed an adequate root system to handle large quantities of water and essentially drowns.
For more information on trees, planting and maintenance guidelines contact your local North Carolina Cooperative Extension office.
Michelle Wallace is the Consumer Horticulture Agent for the North Carolina Cooperative Extension Service in Durham County. You may contact her at 919-560-0525.