The Q&A Archives: Mottled azalea leaves

Question: The azaleas in my yard all start out the season with beautiful green leaves, but as the season progresses the leaves become mottled with light brownish gray spots all over. Sometimes they bloom beautifully, others they don't bloom at all. I suspect a nutrient deficiency or ph imbalance but could use help diagnosing this problem.

Answer: Based on your description I think your plants are being affected by either a fungal infection such as mildew and/or possibly by lace bugs. I would suggest you consult with your local Penn State extension to obtain a more specific diagnosis and based on knowing that, decide how to treat them. If a chemical control is needed, they will have the most up to date informationon what to use and how/when is best to apply it.

Soil for azaleas should be acidic, and the only way to check that is by running some basic soil tests. (In your area, I would expect the soil to be naturally acidic as long as you have not been adding lime to it.) Your county extension should be able to help you with the testing and interpreting the results for growing azaleas. Based on your description, though, the problem is probably not pH.

Azaleas need organic, humusy soil that is evenly moist yet drains well, meaning damp like a wrung out sponge. They are not heavy feeders, so an annual top dressing of compost and possibly also a slow release fertilizer for acid loving plants such as Hollytone should be adequate. Again, though, based on your description, I do not think soil fertility is the problem.

To help your azaleas withstand whatever is affecting them be it pest or disease, give your azaleas good care by providing correct soil condiitons and correct watering and mulching with an acidic mulch such as pine bark.

Over watering and under watering can both cause drooping or wilting due to root damage. Your goal in watering is to keep the soil evenly moist like a wrung out sponge, not sopping wet and not dried out. To know if you need to water, dig into the soil with your finger. If it is still damp, do not water yet. When you do water, apply it to the soil surface and water thoroughly and slowly so it soaks down to the deeper roots. After watering, wait a few hours and then dig down to see how far the water soaked in; it can be surprising.

There is no set schedule for watering, it depends on your soil type and on the weather. Using an organic mulch two to three inches thick over the root area will help reduce watering needs as well as feed the soil gradually as it breaks down over time. Azaleas are shallow rooted and sensitive to mulch that is too deep, so do not over mulch. Also avoid overhead watering and wetting the foliage as that can increase fungal problems, as can poor air circulation.

You should also clean up and remove any fallen azalea foliage and dispose of it in the trash to try to limit sourced of reinfection.

Finally, I should mention azaleas can fail to bloom due to insufficient sunlight, poor soil conditions, excessively cold winter weather, oscillating temperatures damaging the buds, or even late spring frosts that damage the buds. Pruning in summer, fall or early spring will also remove flowering wood. Too, annual leaf loss or damage can reduce the plant's reserves at the expense of blooming.

I hope your county extension can identify the problem for you. Good luck with your azaleas!

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