What is it? The culprit is Rhizoctonia, or web blight. It is a fungus that loves hot, humid weather and damp conditions. Exactly the type of weather that the Heart of Dixie is experiencing now. It starts with dieback of the interior leaves of compact, tightly-growing azaleas - just the type of canopies that we strive for with our plants growing as bonsai. Infection begins in the interior of the plant as the fungus survives in the soil or container rooting medium.
Infected leaves develop brown lesions that enlarge until, eventually, the entire leaf is brown and separates from the stem. The affected leaves often remain matted together by the fungus’s web-like growth (hyphae - For the nerds out there) that holds the brown leaves within the canopy. As the temperature cools in the fall, the fungus stops growing and the matted leaves drop from the plant, unless they are wrapped around a branch where they stay unless picked off.
The disease is a problem for azaleas that are watered from above or constantly wet from frequent rain. Wet foliage, high humidity, and temperatures favor infection. So, try to avoid getting the canopy wet or soked when watering. Also, remove fallen leaf debris from beneath plants. Fungicides can provide some control, apply fungicide at the first sign of disease and continue through the summer months.
There are several fungicides that I find useful for treating this fungus. I use daconil, mancozeb, or Bayer Disease Control. Today, I will be using the Bayer and will apply it every three days until I get this under control. The sad thing about this disease is that it usually attacks in late summer and since it kills the leaves, it often effects the newly forming flower buds, killing them. This ruins your spring showing of flowers.
Start spraying monthly during the growing season to prevent fungus from attacking your azaleas.
