Ever been at a birthday party and get asked about tomato diseases? I have. Ever been at a funeral and get asked about azalea malfunctions? I have. And I couldn’t count the questions I’ve been asked at church in the past 20 years about trees, shrubs, insects, gardens, soil, rabbits, and on and on. I’m not complaining; but I would like to address a couple of things here and now that might help squelch a few of these questions and help you guys have better shrubs at the same time.
Azaleas. Azaleas are our most popular flowering shrub and they are noted for having two main problems. The first one is chlorosis. This is a symptom of iron deficiency and it shows itself as leaves of yellow or very light green rather than the normal deep-green color. The leaf veins are still green, but the leaf tissue between the veins turns yellow.
If your azaleas are showing symptoms of iron chlorosis (a lack of iron), know your soil pH is likely too high for azaleas. Another example of the old Extension slogan "Don’t guess, soil test!" Feeding your azaleas yearly with an acid-forming azalea fertilizer will help solve this problem. You can also use iron sulfate or aluminum sulfate to lower the soil pH around your acid-loving azaleas and other rhododendrons. Never lime the soil around your azaleas!
Another quick-fix remedy for iron chlorosis on azaleas is to spray a chelated-iron fertilizer on the foliage, but lowering the soil pH will be a more long-term solution to the problem.
The other problem most common to azaleas is lace bug damage. I wish I had a quarter for every time I’ve seen this problem. (Nah, best make that a dollar. If I’m going to wish, I might as well make it a good one!) Lace bugs (Stephanitis species) love azaleas growing in sunny places...and they attack as another lesson to the homeowner about planting azaleas in the shade in acidic soils. These insects are small (1/8 inch), but effective enough to stunt your plants. Mature lace bugs are brownish in color and have clear lacy wings (hence the name).
Lace bug damage is most severe in spring and summer. This damage will appear as speckled (mottled) leaves that are yellow and green. On the underside of the leaves are dark-brown spots, the excrement (poop) of the lace bugs. They don’t care if you don’t like it. Their wingless, immature offspring (and the adults) suck the sap right out of your azaleas (from underneath the leaves). That’s where you can find them; under the leaves...on the back side, reducing the food-making capabilities (photosynthesis) of your azaleas.
What to do to stop lace bugs? Use an insecticidal soap in early May before they lay eggs. Thoroughly coat the leaf undersides. If insect numbers continue to build in June, apply an insecticide labeled for shrubs and lace bug damage like liquid Sevin, acephate (Orthene) or dimethoate (Cygon). Follow label directions carefully.
May I also remind you to prune your azaleas after they finish flowering?
It is my hope this information will help you in your pursuit of healthy, happy, beautiful azaleas! Remember – Extension is "the place to go when you need to know!"
Jerry A. Chenault is an Urban Regional Extension Agent with The Alabama Cooperative Extension System, New & Nontraditional Programs division.