Is Your Maple Tree Wilting?

Q. Martin in Denison Iowa writes: "I'm wondering about maple wilt. My neighbor has a large maple tree and the leaves started wilting after it leafed out this spring. Is the tree dying? And will the problem spread to the maple trees in my yard?"

A. I had never heard of {quote} 'maple tree wilt' before (at least I don't think I have; Ducky! Where are my car keys??), and so into the research swamp I went. Although this common name threw me, it turns out that we're talking about a soil-borne disease that tomato growers know all too well: verticillium. I knew that tomato plants grown in the same spot for three years or more would support this disease organism that has a bizarre kind of non-symbiotic relationship with the roots of certain plants. But trees?!

To recap: Grow a tomato plant in what seems to be an ideal spot and get a great harvest. The second year, why would you not plant in that spot again? The answer, obvious to those of us with X-Ray vision, is that a soil-borne wilt called verticillium in the North (and you can't get much more North than Iowa) and its nasty cousin fusarium in the South has been attracted to the roots of that plant, but the numbers aren't great enough to cause any problems.

The second year, you may notice some yellowing of the bottom leaves, but not enough to cause concern. Underground, however, is another story. The wilt organisms are thriving, multiplying at a great rate. But you'll still get your tomatoes.

But by year three, the yellowing will develop sooner and move faster up the plant. This is your final warning. If you plant in that same spot in year four, your Beefsteaks will be deceased by July. Luckily, the solution is easy. Plant in another spot (at least two feet away) the following year, let the original location be tomato-free for two or three years, and the wilt will essentially 'starve to death'. But we're talking trees here, which are much harder to rotate.

Let's turn to a very informative Bulletin from Michigan State University for some answers: "Symptoms of verticillium wilt can be confusing because they are so variable. They include marginal scorch and complete wilting of leaves on individual branches in the crowns of potential hosts. Symptoms can occur at any time of the year but often show up when hot, dry weather begins.

"Sometimes a single branch or the foliage on one side of a tree will die. Trees can go through years where no symptoms are present and then the symptoms show up again several years later. Some trees can struggle along for years, while others may die soon after symptoms appear. In addition to wilting, other symptoms may include small leaves, stunted shoot growth, sparse foliage and abnormally large seed crops."

And I'll add that Non-verticillium problems with these symptoms are legion! They include exposure to winter road salt, 'girdling'(as when mulch is mounded up against the trunk of the tree) over-watering, under-watering, and many more than we can mention. If it's your tree, Michigan suggests you send a sample to The Plant Disease Diagnostic Lab at Cornell, which I heartily endorse. Details on how to take that sample are in the Michigan State article we'll link up to at the written version of this article, which is almost 100% cribbed from the MSU Bulletin. (I'm a poor Public Radio host! Please don't sue me!)

Their suggestions? "Water during dry periods, especially if they occur in summer or fall. Fertilize if needed with a low nitrogen, high potassium fertilizer. Excessive fertilization increases problems with this disease." That means no 10-10-10 or Miracle-Gro, campers! If fertilize you must, use an organic product.

A fascinating note: "Colleagues at the University of Wisconsin have looked at potential hazards associated with use of wood chip mulch from trees infected with Verticillium. They discovered that the pathogen will survive in chips for up to a year." In addition, they note, the type of maple tree is important. Norway maples are easily infected; other maples not so much.

So: what does this mean to our worried maple owner up in Iowa? Verticillium wilt is first attracted to vulnerable trees (under-watered, overfed, growing in compacted soil and especially mulched with wood chips), and especially Norway maples. Plus this disease is, for lack of a better phrase, "root specific". The only way it could transfer from one tree to another is if their roots touch. It is not airborne and insects don't transmit it.

So if your trees look good, don't sweat it. Do water them during especially dry times. Don't do anything to compact their soil, like driving heavy equipment near them. Don't use chemical fertilizers near them and for God's sake: Avoid this horrifying trend of piling wood chips up against the trunk of your trees! Even if the chips aren't infected, they could (and will) eventually kill the tree.

As I've said many times: Have you EVER seen a volcano mulched tree in a healthy forest? Those roots need to breathe and the trunk needs to dry out. Don't fall for the wood mulch scam.