Editor’s note: Kelly R. Jackson takes questions called into his phone recently at the Christian County Extension Office and answers them in the Garden Corner column.
Question. My Leyland Cypress trees are covered in bagworms. Is it too late to spray?
Answer. The best time to tackle bagworm problems are when they first hatch out of the bags in late May or early June. At that point the larvae are vulnerable to any number of insecticides including some organic options like Dipel which contains a bacteria that attacks the bagworms.
In the last few weeks, many gardeners have called our office with severe infestations of bagworms. Control in late summer is much more difficult than early spring because the larvae are protected by their silken bags, still if you have evergreens like Leyland Cypress that are losing large areas of needles, control should be attempted. Acephate (Orthene); Carbaryl (Sevin); Cyfluthrin (Bayer Tree and Shrub); Permethrin (Spectricide Bug Stop) are some products labeled for rescue treatments of trees with bagworms.
Bagworms also feed on maples, oaks and other trees that lose their leaves in the fall. Spraying these trees now is not necessary. Just remember to apply next spring.
If there are few bags and they can be reached safely with a stepladder, consider skipping chemicals and just handpull the bags and drop them in a bucket of soapy water. Every bag left on the tree may contain 300 or more eggs inside waiting to start the cycle over next year.
Q. My tree has a large cavity in the trunk. Should I fill it in or cut down the tree?
A. With as much rain as we have had in July, disease organisms that cause rot have been very active. It is not uncommon for older trees to develop hollow centers due to wood decay. Fortunately, most of a tree’s center consists of non-living tissue. So long as a healthy cylinder of wood and bark 3 to 4 inches in thickness exists around the hollow, the tree could live many years. This does not mean a hollow tree poses no risk to your property or people.
Hazards most often go unnoticed until high winds or heavy snowfall hastens limb or trunk breakage. Where large, hollow trees pose an immediate risk to your home, car or people, consult an arborist to determine ways to lessen your risks or possible removal of the tree. In the past, everything including cement, asphalt, masonry, polyurethane foam, rocks, and gravel has been used to fill tree cavities. This is no longer the practice for several reasons:
1. These materials are very abrasive, natural swaying of the tree leads to rubbing between the materials and the inside surface of the living tissue, allowing decay to expand.
2. These materials do not bend, making a tree more susceptible to storm damage.
3. These materials do not bond to wood and gaps soon occur that trap water and hasten fungal development.
For these reasons, a reasonable course of action is simply to do nothing.
Another old practice is to bore holes at the lower end of a trunk cavity to drain water. This practice guarantees exposure of healthy, living tissue to decay-causing organisms and is not recommended. A water-filled cavity does not speed decay and may actually slow down the process.
Rather than focusing on the cavity, take steps to improve the overall health of the tree. A vigorous growing tree will be able to slow the spread of decay on its own. Moderate fertilization, irrigation during drought, mulching, and aerification by means of holes augered into the soil around the tree may be all a tree needs to halt the progress of decay in its trunk.
Kelly R. Jackson is the Christian County Extension Agent for horticulture. He can be reached at 270-886-6328 or visit Christian County Horticulture online at www.christiancountyextension.com.