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Mr. Smarty Plants - Problem with Eupatorium greggii

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Sunday - April 27, 2008

From: Leander, TX
Region: Southwest
Topic: Pests, Herbs/Forbs
Title: Problem with Eupatorium greggii
Answered by: Barbara Medford

QUESTION:

At the Garden's fall plant sale in 2006, I bought some Eupatorium greggii. It did very well last year. Recently, the entire plant looks like it is just wilting from the top down, as if it has some sort of disease. Moisture is not the problem. The Conoclinium greggii I have elsewhere does not seem to be affected. Do you have any idea if this plant is prone to a virus? Any other ideas?

ANSWER:

Eupatorium greggii is now considered a synonym for Conoclinium greggii (palmleaf thoroughwort), which explains why we couldn't find Eupatorium greggii in the Native Plant Database. Beyond that, however, we are still very puzzled as to what could be causing your plant to decline. Have you checked for red spider mites or whiteflies? Try tapping an affected leaf over a sheet of white paper-if you get little red spots, that's red spider mites. If you see what looks like flying dandruff, that is whiteflies. Honeydew excreted by whiteflies glaze both upper and lower leaf surfaces, causing the development of black sooty mold fungus. Just about every reference we checked referred to Conoclinium greggii (palmleaf thoroughwort) as almost pest and disease free, but you may have gotten caught in the "almost." The only other possibility we could think of is that this plant needs afternoon shade, and if it is in full sun all day, it will need additional water. These are very sturdy plants, and spread by rhizomes, which sometimes makes them almost a nuisance, but they are wonderful for butterflies. We would suggest that, if you feel the insects mentioned are the culprits, that you first trim out all the affected foliage, and dispose of it where the insects living on it will not be transported to other plants. Then try a weak solution of Safer insecticidal soap, sprayed on it two or three times in a week, because of the various stages of development the whitefly goes through. The main point is to prevent the spread of these insects to other plants in your garden, so you'll need to keep a watch out for that.

 

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