Is this blight on Black-Eyed Susan? Why?

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ShaynaPearl Maynard, MA Aug 07, 2013

I have many clumps of black eyed susans. The flowers look good on most--not all--but the leaves are turning black on most of them. Is it blight? Something else? Why? What to do?

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ken33 Bowling Green, OH Aug 07, 2013

Could be septoria. At any rate many black eyed susan diseases are caused by overwatering and overcrowding. Is this clump of flowers in a low spot that gets more water? Are they overcrowded? Check out figures #2 and #3 at this link: http://www.extension.umn.edu/yardandgarden/ygbriefs/p154rudbeckiadisease.html

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ShaynaPearl Maynard, MA Aug 07, 2013

Thanks, ken33. It does indeed look like septoria, though it's been a dry, hot year mostly, and I didn't water much to make up for what the heavens weren't offering. It could be overcrowding in some places. I wonder if it is also spread from last year. I think I had a bit of it then, but didn't pay it much mind.

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ken33 Bowling Green, OH Aug 07, 2013

The following pertains to septoria.

A good way to start dealing with this is to plan on digging and dividing your susan patch right after Labor Day. This disease tends to be worse in crowded conditions when poor air circulation encourages leaf dampness. If you divide off fist-sized pieces and space them about 2 feet apart, that should help next year.

Another good move is cutting off and removing all the infected foliage from the garden this fall. Septoria spores overwinter on plant residue, so the more of these you can get rid of, the fewer spores you'll have to reinfect next spring.

The third prong of attack, if you need/want it, is spraying a protective fungicide. The key is getting that on starting around early June and then re-spraying every 7 to 10 days while the conditions are ripe for infection. Daconil (chlorothalonil) is a common chemical fungicide that usually does the job, but good organic options are copper, one of the new bicarbonate fungicides (i.e. GreenCure, Remedy, Bi-Carb) and possibly neem oil.

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drobarr Hummelstown, PA(Zone 6b) Aug 07, 2013

I have had the same problem. Some varieties of Rudbeckia are more susceptible than others.

Follow Ken's treatment plan should work well.

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ShaynaPearl Maynard, MA Aug 08, 2013

Sounds like great advice. Thanks, Ken, and to drobarr for seconding it.

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