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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis
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Maple Leaf Problems - Anthracnose and Bladder Gall

Posted by John Fulton -

We may be running about three weeks behind normal, but some things are catching up with a vengeance. Anthracnose leaf fungus is one of them. If you haven’t noticed, maple tree leaves on the better quality maples, such as red maples and sugar maples, are browning or drying up in many locations.

Anthracnose starts as dead leaf areas between leaf veins, or on the tips of leaves. When severe enough, leaves will fall. Several of the infected trees have actually had the leaves turn completely black already. It is much more noticeable on one side of many trees as well, due to air movement carrying the disease and drying out foliage quickly. The good news is that it rarely harms trees. If enough leaves drop, a new set comes out in 4-6 weeks and we start all over. The next set of leaves may also get the disease, but they may not. Infection can continue with weather favorable to the disease, and when nighttime temperatures stay under 65 degrees. Treatments when you see the symptoms of this disease are simply wasted time and money. The old “water and fertilizer routine” is about the best you can do.

“Soft maples,” or silver maples are showing symptoms of maple leaf bladder gall. Same song, different dance. The gall is yellow to red when it starts out, then turns brown as the year wears on. The cause is a mite feeding on the leaf. The leaf then swells in response to the injury and toxins put into the leaf. The “bumps” are actually leaf tissue. I usually compare it to you getting a mosquito bite. There is no treatment, since the swellings are actually leaf tissue, and there is no damage other than the unsightliness.

Apple scab is a disease similar to anthracnose, and can cause premature leaf drop in apples and crabapples. If you are on a regular spray schedule for fruit trees, it should prevent most of the problems. You could also spray crabapples this way, but you would have to weigh the cost and benefit since no fruit production is involved.

As a reminder, spray programs for disease prevention in fruit trees should be applied every 10-14 days after the bloom period is over. It should be stressed that these are preventative programs, and not curative. These programs then continue until roughly two weeks before the fruit is ready to harvest.

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