Lacebugs may be cause of azalea woes
Q: We have a recurring problem with 10 ‘Mrs. G.G. Gerbing’ azaleas located in semi shade on the south side of our home. They’re 18 years old and 6 feet tall.
After blooming, we fertilize, and the new growth is quite good. But in June-July the larger leaves turn yellow, sometimes have black spots and drop. We can’t detect any insects on the affected leaves.
There is a very large azalea on the north side of the house that has no problems.
Could the problem be related to a lack of nutrition or a soil condition? Soil moisture is fairly constant. Wolfgang Schweyer, Sugar Land
A: Age, environment or nutrition can trigger yellowing azalea leaves. Often, leaves yellow and drop with age. However, since your problem occurs in summer, check the leaves for lacebugs, insects that drain chlorophyll and plant juices, leaving the foliage yellowish, stippled or silvery. You’ll likely also find dark specks, the lacebugs’ excrement. Use a magnifying glass to look for the insects with gauzelike wings as well as their poop on the leaf undersides.
Frequent sprays with the garden hose, making sure you hit the undersides of the leaves with strong blasts of water, can discourage populations. Lacebugs aren’t usually a serious threat if you can keep them under some control, but the damaged leaves will not regain an allgreen appearance.
A number of pesticides can be used to control lacebugs, including insecticidal soap, summer horticultural oil and pyrethrum/rotenone mix. Or spray a mixture of 1 ounce soybean oil and 1 ounce orange oil in a gallon of water over the plants. Also douse the undersides of the leaves.
I’ve found that azaleas in sunnier spots can be more prone to lacebug problems.
If you think the dark spots aren’t insect excrement, perhaps there’s a fungal problem. Remove fallen infected foliage. Spray the plants with neem oil and drench the surrounding soil with it. Some apply agricultural cornmeal (make sure it’s milled) around the shrubs. Take fallen infected foliage in a sealed plastic bag to a certified nurseryman to help identify the problem and determine the best solution.
Leaves also may yellow if the soil is too dry or wet.
A common problem is chlorosis, which results in yellowing between the veins in the leaves.
Azaleas like a well-draining, moist, organically enriched
acidic soil. In our typically alkaline soil, the plants can’t absorb enough iron and other nutrients to remain green, and the leaves become chlorotic. In September and February, sprinkle powdered sulfur beneath the shrubs; water it in to increase soil acidity. Mulch.
Q: I have a dozen mature bottlebrush (most about 15 feet tall) in my backyard. They are full of hummingbirds and butterflies all the time. A couple months ago, about half of them suddenly turned brown and died. Is there something I should know about saving my remaining bottlebrush? Ron Honefenger, Houston
A: This sounds like the results of the root rotting fungal disease phytophthora, exacerbated by wet conditions and perhaps latent freeze damage. If there is any sign of life in the shrubs, you might prune and drench the soil with a fungicide. If not, remove, then drench the soil with the fungicide before replanting.
Make sure there’s good drainage, as wet soil encourages problems. You might spray the remaining shrubs and drench surrounding soil as a preventative.
Ask your nurseryman for suggested products.
Q: What can I do to repel wasps that attack the butterfly caterpillars on my passionflower vine? Beverly Hicks, Houston
A: Passionflower vine is a host plant for the Gulf fritillary butterfly, and other butterflies like the nectar found in the exotic blooms.
It can be disturbing to watch predatory wasps do away with butterfly caterpillars. Those who garden to help rebuild monarch butterfly populations are especially aggravated when the paper wasps carry their young off.
I wish there was an easy answer. While some let nature take its course, others have tried various tactics to save the future butterflies. Some build protective screens around host plants that are laden with eggs and caterpillars. Others snip plant parts with eggs and caterpillars and protect these in a mesh laundry hamper or commercial butterfly house. And there are those who swat wasp with bug zappers.
You could try to locate and destroy the wasps’ nest. But I wouldn’t guarantee this to be a cure all. Avoid spraying near your vine as you’ll harm the insects and their offspring.
The larger the vine, the more butterflies and caterpillars, so maybe the greater numbers will have a better chance against the wasps.