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What’s Wrong With This Tree?Master Gardener – March 23, 2016

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What’s Wrong With This Tree?

CrossSection-OakGall 1 BW.jpg

By Will Summers,

Master Gardener

Trees represent one of the greatest investments in our home property value. Experts agree that a healthy, mature oak may add $10,000 or more to property values. Whether you consider the monetary value or look deeper into the aesthetic value, trees provide a lasting benefit to us all.

This article provides information gained from the recent U of I Extension class held in Mt Vernon. I cannot list all likely tree problems you may encounter, but I share the more common tree concerns found in south-central Illinois. Here are some words of advice offered by the experts.

Tree Damage – Most tree ailments start from some sort of injury. Injuries include lawn mower – weed-eater damage, vandalism, animal damage and even faulty pruning practices. Injuries open sensitive plant tissue to disease infection, invasion by an organism or both. Insects are often the cause or the carrier. Use the approved 3-step cutting method, and try to limit all limb removal to less than two inches in diameter. Do not use “tree-wound sealer” or paint on any tree cut or wound. Try to keep limb removal to the winter season when parasites and infection are least likely to occur. Tree damage is the most likely place where a sick tree will incur disease. Secondly, healthy plants are accustomed to surviving a degree of problems without becoming decadent. Planting the right tree in the right place is critical to growing a healthy tree. If a tree is planted beneath powerlines or too close to a permanent structure such as a road, building foundation or pavement, then your tree is predisposed to illness. Lastly, incorrect pruning practices, such as “topping” which leaves stub ends of large branches, nearly always spells a slow, agonizing death to any tree.

Emerald Ash Borer (or “EAB”) will soon become common in our area. The EAB is a half-inch long, iridescent green beetle that infects all species of ash common to our area. Just as the Dutch Elm Disease wiped out most American elms fifty years ago and the chestnut blight caused the disappearance of all American chestnut more than eighty years ago, the EAB has its sights on Southern Illinois today. Regrettably, this page in our history is only now being written. My objective here, if you have ash trees, is to keep them healthy.

“Do Not Move Firewood” is the first rule to slowing the EAB problem. Hopefully, science will come up with a solution before EAB wins this battle.

Records show that after the chestnut trees all died, people planted American elm. After the elms died, people planted ash trees. Today, people have planted too many ash trees which predisposes this species to the EAB epidemic. As they say, the best defense is a good offense, to anyone wishing to plant a tree this spring. You should look for a species not so abundantly planted. The rule-of-thumb for any homeowner or municipality is to never let one species of tree represent more than ten percent of your trees and let no one variety of tree consist of more than five percent of your landscape. Usually infections and infestations only occur on one tree type. The objective here is to plant for a diversity of species and plant types.

We are in the very best time to plant all species of trees. Any delay now results in less desirable conditions for tree establishment. Containerized trees have the highest survival. We recommend planting small trees rather than going through the expense and difficulty of planting large trees. Large trees experience greater transplant shock which may stunt a tree’s growth for several years. Within ten years, that small-ish tree will overtop the larger planted tree.

Some short solutions:

Homeowners frequently seek to control oak gall. Oak gall is a tiny fly that lays its eggs in the tree stem and the tree reacts by hormonally accelerating growth around where the insect nymphs feed. Historically, oak gall only decreased the appearance but did not cause serious injury. Infestations are limited primarily to pin oaks but also, surprisingly, to shingle oaks. Again, this is because pin oaks are most frequently planted street trees. The only control is to cut out as many galls as possible and dispose of the galls by burning.

Anthracnose infests sycamore and London planetrees in spring causing the first set of leaves to wither and die. This disease is spread by raindrop splash and birds’ feet. Control is not recommended for this fungal disease due to the size of most trees and the need for continued treatment.

Regarding tent caterpillars in cherry trees: Pull off the bugs, tie in a plastic bag and toss in the garbage.

Bagworms feed on evergreens such as arbor vitae and spruce: Hand pick as early as possible, tie these in a plastic bag and dispose in the garbage.

For more information regarding control of tree diseases and pests, please contact your local master gardener, the University of Illinois Extension Office and your local public library.

A cross-section of Oak Gall.