Garden Q&A: insects suspects in azalea damage
Q: I have several azaleas in front of my home that have been there for approximately 15 years. Last fall I noticed one of them had black on the branches and on the rock underneath. This spring it seems to be spreading. What is this? Is there anything I can do to stop it?
A: I suspect that there is an insect to blame for your azalea issues; the only trouble is, I'm not positive exactly which insect it is. I'll describe two different problems, and you'll have to do the detective work to determine exactly who the culprit is.
When a black, splotchy substance is found on areas around and underneath a tree or shrub, as well as on the plant itself, I feel confident that it is a fungus known as sooty mold. Sooty mold itself is not a big problem, other than the fact that its presence on foliage can cut down on photosynthesis. The real problem is that the sooty mold is there because it is feeding on “honeydew” — the sweet, sticky excrement of several different soft-bodied insects. When you see sooty mold, it is nearly certain that there is an insect issue to deal with.
Look along the stems of your azaleas and on the leaf undersides for signs of pests such as mealybugs, scales and aphids, all of which excrete honeydew. You can search for images of them on the Internet to help you properly identify them or take a sample to a nursery in a sealed, plastic baggie. The aphids and mealybugs are fairly easy to manage with horticultural oil or insecticidal soap. Scale is a bit tougher because of its hard shell, but it, too, can be managed with a neem-based organic insecticide.
The other insect that may be plaguing your azaleas is lace bugs. Lace bugs are very tiny (1⁄8 inch), dark insects with lace-like wings. They can be found on the leaf undersides along with small black spots of their excrement (known as tar spots). These tiny black specks of excrement do not wipe off and, in severe infestations, can be found on items beneath affected plants. Damage to the leaf surface appears as whitish dappling, and even when the insects are eliminated, the discoloration will remain. Lace bugs also can be controlled with horticultural oil, insecticidal soap, or neem-based insecticides applied to all leaf surfaces.
All four of these insects are quite common on azaleas and rhododendrons planted in locations that get too much sun. Azaleas and rhododendrons are shade-loving, understory plants, and when they are sited in full sun, they are weakened and prone to insect attacks (in wooded areas, where these plants are well-adapted, we almost never see issues with insect pests like these). If your azaleas are in full sun and you want to prevent this problem from repeating itself, you may want to consider replacing them with a sun-loving shrub variety or relocating them to a shadier spot.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is www.jessicawalliser.com.
Send your gardening or landscaping questions to firstname.lastname@example.org or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
Show commenting policy
TribLive commenting policy
You are solely responsible for your comments and by using TribLive.com you agree to our Terms of Service.
We moderate comments. Our goal is to provide substantive commentary for a general readership. By screening submissions, we provide a space where readers can share intelligent and informed commentary that enhances the quality of our news and information.
While most comments will be posted if they are on-topic and not abusive, moderating decisions are subjective. We will make them as carefully and consistently as we can. Because of the volume of reader comments, we cannot review individual moderation decisions with readers.
We value thoughtful comments representing a range of views that make their point quickly and politely. We make an effort to protect discussions from repeated comments either by the same reader or different readers.
We follow the same standards for taste as the daily newspaper. A few things we won't tolerate: personal attacks, obscenity, vulgarity, profanity (including expletives and letters followed by dashes), commercial promotion, impersonations, incoherence, proselytizing and SHOUTING. Don't include URLs to Web sites.
We do not edit comments. They are either approved or deleted. We reserve the right to edit a comment that is quoted or excerpted in an article. In this case, we may fix spelling and punctuation.
We welcome strong opinions and criticism of our work, but we don't want comments to become bogged down with discussions of our policies and we will moderate accordingly.
We appreciate it when readers and people quoted in articles or blog posts point out errors of fact or emphasis and will investigate all assertions. But these suggestions should be sent via e-mail. To avoid distracting other readers, we won't publish comments that suggest a correction. Instead, corrections will be made in a blog post or in an article.
- State Supreme Court Justice McCaffery sent explicit emails
- West Newton man found dead in helicopter wreckage near Rostraver Airport
- Rossi: Pirates can’t waste McCutchen’s prime
- Giants’ Crawford makes history with slam
- Truck accident closes all eastbound lanes of Parkway West
- Penguins’ Sutter is determined to keep scoring pressure on
- Penguins release Carcillo from tryout contract
- East Huntingdon man dies following police chase
- Steelers pressing to create opportunities to get to quarterback
- Giants, Bumgarner shut out Pirates in wild-card game
- Bumgarner quiets Blackout crowd with 4-hit shutout