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CANKER SORE

Q

I have an oak tree, which I believe is a water oak, that has bark falling off in patches around the trunk. The top of the tree isn't looking very good, either. Any idea what is wrong with my tree? — Texas

A

You may be describing Hypoxylon canker, a fungal disease that attacks stressed oak trees, as well as sycamore, maple and elm species. The Hypoxylon fungus is considered a weak parasite, in that it cannot attack healthy trees. Trees that have been weakened or damaged from construction, compaction, environmental stresses or repeated attack by leaf-feeding insects are prime targets. Thinning of the crown is typically the first sign of disease, but the bark peeling at eye level usually alerts people to the problem. Depending upon the species attacked, the wood under the bark may be covered with tan-, green- or brown-colored spores, which will change to dark brown or black and become tarlike in appearance. They will finally turn a silver gray. Once the bark begins to fall off, the fungus has become entrenched in the tree and death is certain. As with most canker diseases, there is nothing that can be done to cure the tree. Preventing other trees from suffering the same fate should be your goal. Protect trees in construction areas by fencing off a wide area (larger than the drip line of the tree). Do not pile soil onto the trunk or onto the area around the trunk (the roots will suffocate, resulting in stress to the tree). Water when droughty, and be careful with turf and landscape herbicides, especially three-way broadleaf herbicides.

STANDING TALL

Q

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I have a situation where thousands of people will be treading on our newly renovated downtown square over a weekend (during a festival). In the past, I have always directed staff to skip mowing it the week prior to the event in order for the grass to get a little higher as I have been told that longer grass blades and less stress will help to have the grass “bounce back” after the event. Is this a known practice or am I only setting myself up for criticism because the grass is too long? — Highland, Ill.

A

It's tough for some turf managers to have their beautiful turfgrass tread upon, especially when it primarily is grown “for show.” Unlike athletic field managers and golf course superintendents, your main objective is to provide nicely manicured green carpet to offset the rest of the park or site features. What athletic field managers and superintendents do weekly, you will need to do for your festival. For your festival, be sure your turf does not suffer from drought stress. Less frequent, but thorough, waterings will help promote a deep root system. Do not irrigate within 24 to 48 hours prior to the event, unless the turf is under stress. Excess water in the soil would act as a lubricant, moving soil particles around and closer together, resulting in more compaction. Aeration will help promote a deep root system, by allowing sufficient oxygen to penetrate deeper into the soil. Mowing as tall as practical will help develop a deep root system, too. As for not mowing the week prior to the event, the taller grass will provide some cushion to protect the crown of the plant as well as a tiny bit of compaction prevention. A week's worth of long grass should not be upsetting to most people.

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