March 10, 2010

More fallout from this year's overwatering: Plant diseasesASK THE MAINE GARDENER

— The leaves are falling, and it isn't fall.

All across Maine, a fungus called tar spot of maple is producing black spots on maple leaves, causing them to curl up and drop off.

Bruce Watt, a plant disease specialist at the University of Maine Extension in Orono, says he has seen the disease in the Bangor-Brewer area, and it is moving to the coast.

And -- what a surprise -- you can blame the wet weather.

''It was sort of building up last year,'' Watt said, ''and we saw more of it this spring. It was so very wet, and wetness is a requirement for the spore of this fungus to germinate.''

The fungus overwinters on the leaves on the ground, and in the spring, the spores shoot up in the air, get caught in the wind, and can go all the way up to the crown of the trees.

I know of people in South Portland and Bath who are dealing with tar spot, but I haven't seen it in my area of Cape Elizabeth.

Watt said the tar spot seems to be doing the most damage to sugar maples and Norway maples, but it can affect all maples.

And the areas Watt saw in Bangor that had the most damage were where the leaves had not been raked up but allowed to stay under the trees.

So there is an extra reason to get the leaves raked this year.

But, Watt said, don't compost them at home unless you have a compost system that generates enough heat to kill the spores. Most homeowner compost bins don't get that warm.

Watt doubts the tar spot will affect fall-foliage colors much. He doesn't see the disease that often when he walks in the woods.

Don't think that if you have oaks you are -- sorry -- out of the woods. A neighbor brought over some crinkly, dead oak leaves from one of two oaks on his property.

Watt and William Ostrofsky, a forest pathologist with the Maine Forest Service, said the disease probably was anthracnose, another fungus. The ''probably'' is because it is tough to diagnose over the phone.

Ostrofsky said the anthracnose of oaks has been a problem in coastal communities around Camden, and could easily have made it to Cape Elizabeth.

The disease is weather-specific, and while the classic recommendation is to rake and compost the leaves elsewhere, Ostrofsky said you can't get all the leaves, no matter how well you rake, so you can't get rid of the disease.

But the oaks have had their leaves all summer and are about to lose them anyway, so the anthracnose does no real damage to the trees.

Watt said that with all the wet weather, this has been one of the worst years he can recall for plant diseases -- especially late blight, which attacks tomatoes and potatoes especially, and can occasionally hit eggplants and peppers.

Watt said he had just seen late blight on his tomatoes -- his wife thinks he brought it home from the office -- and was planning to spray his tomatoes with a copper fungicide approved for organic gardens by the Maine Organic Farmers and Gardeners Association.

When I mentioned that a section of potatoes right in the middle of my plot had died back seemingly overnight, he said he had heard that from other organic gardeners as well.

One variety -- and the labels got lost, so I am not sure yet which one -- apparently was more susceptible to the blight.

My tomatoes showed early signs of some sort of fungus, so I followed Watt's copper fungicide directive. I hope it works.

Tom Atwell can be contacted at 791-6362 or at:

tatwell@pressherald.comQ: Our hostas are the very large variety, and they are now full of holes (from critters?) and the flowers have faded and are huge and drooping. they look pretty ragged and make the whole garden look rather sickly. Can we cut them back now, like we do in the fall? Or is it too early?

A: I would cut off the flowers now, but wait until fall before cutting off the leaves.

Q: Two of my purple Echinacea have been slowly dying, leaf by leaf, from the ground up. Could this be some sort of fungus due to the wet weather? I thought Echinacea were a hardy perennial? Others have been self-sowing around the garden and are healthy. What do you think? -- John Butke, Boothbay

A: Nancy and I have seen something like this with some of our rudbeckia. I don't know if it's a fungus or a disease. Nancy has been cutting them off close to the ground and disposing of the dried leaves and so forth, not putting them in our compost, just in case it is a disease. I have been thinking that it might be because there was so much rain that the velvety leafed rudbeckia wasn't drying thoroughly and a mildew sort of thing was happening. I have no idea what you have, but I would advise that you cut down the offending stalks and not put them in the compost.

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