what is wrong with these leaves on rhododendrons and kalmia?

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msmouser Lexington, MA(Zone 5b) Jun 13, 2009

HELP What is causing this problem on my rhododendron and kalmia leaves, but NOT on my roses?

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snapple45 Holland, OH(Zone 5b) Jun 13, 2009

I think it's Cercospora leaf spot. Sanitation ( disposal of all dropped leaves ) and a fungicide can control it. Before they removed it from the market Benomyl would have been the fungicide usually reccommended. These days Bayer Advanced is an option. It's a systemic. You use it as a soil drench. Or read labels to find a spray fungicide. Fall cleanup is important. You should treat early next spring to prevent reinfection.

http://www.clemson.edu/extension/hgic/pests/plant_pests/shrubs/hgic2050.html
http://www.bayeradvanced.com/product/Dual-Protection-Azalea-Insect-Disease-Control/concentrate.html

The joys of gardening. Both of your affected plants are in the same family - Ericaceae. They are susceptible to Cercospora handelii. Roses are in the Rosaceae family. While they have notorius susceptibility to leaf spot diseases , particularly Cercospora rosicola, they aren't susceptible to C. handelii.

Post #6680597
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msmouser Lexington, MA(Zone 5b) Jun 13, 2009

Thank you for your extremely imformative and helpful answer, snapple 45. I really appreciate your help.

msmouser

Post #6682755
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claypa West Pottsgrove, PA(Zone 6b) Jun 13, 2009

I've had this on a rhododendron, and it just went away. It's weather-related too, so it might not happen again. If your shrubs just have a few leaves like this, I wouldn't be too concerned. Not to contradict snapple's advice, but I've never seen a rhododendron that's worth using that bayer stuff, and I love rhodies and azaleas. Of course that's a personal choice we each have to make.

http://www.umassgreeninfo.org/fact_sheets/diseases/rhododendron_leaf_spot.pdf

Post #6683219
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snapple45 Holland, OH(Zone 5b) Jun 14, 2009

I just applied my second treatment of the season to some 7' azaleas that are otherwise plagued by powdery mildew every year so badly they sometimes lose their leaves. So I guess it is to each his own. I do love my 7 footers. ;)

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