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Joined: Mon Aug 11, 2008 5:43 pm
Location: SE Michigan

powdery mildew, mold and spiders

I've had my perennial garden for 14 years and one section of it just seems always susceptible to disease. There is nothing different in this part other than it gets a little less sunlight. But this year it's getting attacked by something different (I think). First of all, my bee balm always gets mildewy leaves after it's done blooming. Really ugly, so I cut that back. But then many of my other plants (in particular echinacea, daisies, clematis and mums) start dying off from the ground up -- the leaves turning black and falling off. Although they generally bloom, the plants don't look particularly healthy. And a first for me this year -- my creeping phlox seems to have acquired spiders or something that is killing it off in patches. In the early morning dew, you can see the webs covering portions of the plants -- and now those webs are creeping further into the garden. I live in Michigan where it's generally hot and humid. This year we started off with more rain than usual too. I've sprayed with organic soap which doesn't seem to affect whatever is making the webs. Any guesses on what is going on and how to control it? :roll: Thanks!

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Joined: Tue Jun 24, 2008 5:04 am
Location: Oregon

Welcome to the forums! :)

You can be assured that if your plants indeed have spiders, the spiders aren't the cause of any damage. Spiders eat insects, not plants. They would happily live on your plants if there were insects there for them to capture and eat, however.

OTOH, spider mites do damage plants by sucking the sap. Spider mites create webs, too, but the mites are very small. You will need a magnifying glass to see them, and you will find them on the undersides of the leaves. The insecticidal soap should kill the mites, but you have to be sure you spray the plants thoroughly, especially the undersides of the leaves, as well as all the stems. You have to do repeat sprayings at 10 to 15 day intervals to kill any new mites that hatch. I usually find 3 sprayings sufficient, but it would probably depend on how badly infested your plants were. (That assumes, of course, that spider mites are even the cause of the problem.)

I'll have to leave the answers to your other questions for more knowledgeable members. I can think of a lot of different things that might be causing the black leaves, but all I could really offer would just be a guess.

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