Hydrangeas in trouble! - Knowledgebase Question

swanzey, Ne
Avatar for indainfoodro
Question by indainfoodro
August 19, 2010
Some of my hydrangeas has yellow leaves and one of the plants leaves looks like it has little white spots. Two weeks ago I put the hydrangea fertilizer and it was doing well until we had a big rain storm! And now I need HELP! thank you very much.

Answer from NGA
August 19, 2010
Yellowing leaves can be a sign of heat stress or of water stress. Since you've had a lot of rain, the excessively wet soil may be the cause. Of more concern are the white spots you're seeing on the leaves. They could be the initial stages of a fungal disease called powdery mildew.

Early signs of powdery mildew are small circular white spots with feathery edges scattered on the lower surface of the leaves. This disease will increase until it covers all the leaves and shoots.

You can try to stop the spread by removing all the affected leaves. If it continues to develop, you may need to spray with a fungicide. These include: sulfur, neem oil (Rose Defense, Shield-All, Triact), triforine (Ortho Funginex), or potassium bicarbonate (Kaligreen, First Step). Be sure to apply according to label directions.

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