Why are my black-eyed susans getting black spots on their leaves?
by
Sally
I live in Cecil County, MD near the Susquehanna River, off the corridor of I-95. We've had really hot days and dry days for two weeks. Do you think that may contribute? Just got rain today.
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If they received no water, or water in insufficient quantity, that may be the problem, if they were previously o.k. Try removing the affected leaves. Fertilize at 1/3 strength, then water, well. Make a mound of mulch around them (but not against center stem), if you have to, to avoid water run off, which typically occurs in this weather (if you try digging into surrounding earth, you may find bone dry soil, as much as 6" below the surface, and it may be very hard). When watering in this weather, water only at the base, to avoid sun scald.
Otherwise, they may have developed a soil borne fungus. Check to see if other plants are affected.
A variety of reasons can cause but this might help get rid of the black spot fungus
https://www.gardeningknowhow.com/plant-problems/disease/black-spot-fungus.htm