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MSU Extension Service

Home Grown is an educational, entertaining, question-answer column seen weekly in "News from the Genesee MSUE Office," a weekly newsletter for Genesee County Master Gardeners. Special thanks to the Genesee, Oakland and Livingston county MSU Extension offices for providing this service.

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This week's HomeGrown

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The leaves are really falling off my giant maple. As I was raking them up, almost every leaf had black spots. I think this is a fungus and I know that this has got to be a problem. How do I prevent this next year?

Your perceived problem is called Tar Spot. But consider this. Itís November and the leaves are falling after a hard frost. How much of a problem is this really? The problem is more with the leaf raker than the tree. Tar spot is a fungus that enters the leaves in late spring or early summer. We need humidity for this to happen. It incubates in the leaf for one or two months. Then the leaf develops light green or yellow spots. These are the places that the black, shiny spots will be developing. This fungus will affect many kinds of maples. It has been described as ďÖthe most showy and least damaging of the foliar diseases.Ē That translates into virtually no defoliation or tree misery. The way tar spot begins is with the infected leaves from the season before. If you are determined to control this, begin by picking up every spotted leaf and destroying it. Make sure you get all those crunched leaf bits you created by walking on them and raking them. Once this is done, go to every neighborís property that touches yours and do the same to their maple leaves. Then, do their neighbors. You would have better luck installing a monster dehumidifier. This is kind of like having a pimple. You might not look as cute but it doesnít hurt you.

I have some kind of short-needled spruce trees that are getting tan or yellow needles all over. A bunch of these are close to the trunk but some go all the way to the end of the branch. I know that you are going to ask about them getting watered. We have a lawn irrigation system so I know this isnít the problem. So what do I do?

Water them. Except this time, drag the hose out there and water them deeply. A lawn irrigation system is designed to keep grass happy. This means that the soil only has to get damp to a depth of about two inches. The spruceís roots are in the top 18 inches of soil. We had a whopper of a drought this year. Many areas still havenít had a decent rain. This means that there is no moisture in the soil. Two pathetic inches of moist soil isnít going to help trees. When you water your trees, water the imaginary four points of the compass. Trees can pull in water on the side where it is but canít move water around to the other sides of the tree. Put the hose halfway between the trunk and as far out as the branches reach. Whatever way the water runs is just fine. If this is a good-sized tree, roots will be growing beyond the length of the branches, so at some point, water that soil, too. Thatís another shortcoming of an irrigation system that only hits one side of a tree. If you feel that the irrigation system has done a good job, dig down in the soil about 12 inches. If the soil is moist all the way down and below this, youíre fine. If the soil is dry, water the trees. You donít need to be an arborist to do this. Any needles that have turned tan or brown will not recover. You are attempting to save the others. Evergreens will show damage as much as six months after the problem event. Your trees could be showing damage from July. If these trees arenít rehydrated before winter, they will probably look much worse next spring. Some of your interior brown needles could be natural shedding of older needles but loss of needles on the ends of branches is bad news. Water.

Gretchen Voyle, MSU Extension-Livingston County Horticulture
Agent 517/546-3950


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