Zinnias - Knowledgebase Question

Seymour, In
Question by jangessling
September 21, 2010
This season the leaves on my zinnia flowers had a disease and some type of insect eating away at them. The leaves had white powdery spots,along with holes that would become transparent.I thought it might be moths or caterpillers, and fungus, don't know what to do to prevent next year. Can you please advise? Thanks


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Answer from NGA
September 21, 2010

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What you describe sounds like a fungal disease called powdery mildew. It's a common problem with zinnias late in the growing season. To reduce additional infections, avoid overhead watering to help reduce the relative humidity. Remove and destroy all infected plant parts (leaves, etc.). Selectively prune overcrowded plant material to help increase air circulation. This helps reduce relative humidity and infection. If cultural controls fail to prevent disease buildup, or if the disease pressure is too great, an application of a fungicide may be necessary. These include: sulfur, neem oil (Rose Defense, Shield-All, Triact), triforine (Ortho Funginex), or potassium bicarbonate (Kaligreen, First Step) Chemicals are most effective when combined with cultural controls. The holes that you're finding are most likely from caterpillar feeding. You can control caterpillars with Bt (sold as Dipel or Thuricide). Apply according to label directions. Best wishes with your landscape!

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