spots and yellowing, hibiscuses - Knowledgebase Question

desert hot springs, Ca
Question by dongc
March 14, 2010
I have several hisiscus plant and they are getting black spots and the leaves are turning yellow. Some of them look like the have been eaten. what might cause this. One of them is blooming some much that the leaves are almost all gone also.


Answer from NGA
March 14, 2010


The black spots are probably a fungal disease (it's hard to diagnose a plant without seeing it!) and the holey leaves are most likely showing damage from caterpillars. Look on the undersides of the leaves for little green caterpillars and look for frass (bug poop) on the upper sides of the leaves directly beneath the damaged leaves. If you find caterpillars or frass, you can spray with Bt (sold as Dipel or Thuricide) to control the pests. The fungal disease may respond to a fungicide but it might just be easier to prune away the damaged plant parts, then use Bt. This will remove the fungal spores and control the caterpillars. Hibiscus takes hard pruning well, especially early in the season. The new growth will be healthy and you'll gets lots of flowers in about 4 weeks. Best wishes with your hibiscus.

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