Garden Q&A: Fight 'rose slugs' with parasites
Question: I am a 93-year-old man who is going to lose two beautiful 25-year-old rose bushes that are being destroyed by some very hungry little green worms. There is nothing but leaf-veins and stems left! I was told what to spray on them, but it was to no avail. Can you tell me what to do? You will make my wife and I very happy old folks.
Answer: The small green “worms” you describe on your rose leaves are a type of sawfly larvae that can quickly skeletonize leaves. With tiny green bodies that measure a mere one-eighth to three-quarters of an inch and light brown heads, they are caterpillar-like in appearance but are not true caterpillars. Though there are sawfly species that attack many different plants — from hibiscus and pines to hollyhocks — this particular species is commonly known as rose slugs.
Rose slugs are most frequently found on the undersides of leaves, and because of their small size, they can be difficult to find. Hand squashing the larvae is an option, but because they are so tiny, you could spend a huge amount of time and energy to control them in this manner.
A better bet would be to rely on several beneficial insects who parasitize and prey upon sawfly larvae. Each year, interplant your roses with plants like sweet alyssum, wallflower, lemon balm, cilantro and other flowering herbs. These plants attract many species of parasitic wasps and tachinid flies that naturally control sawfly larvae by using them as hosts for their maturing larvae. You'll be surprised at what a huge difference the presence of these plants makes on the population of many pests, including sawfly larvae.
Effective organic product controls are another option, but they should only be used as a last resort, when the damage is extreme and the health of your plant is at risk. As with any products, organic or conventional, you must be sure to follow label instructions carefully.
Look for products with the active ingredient spinosad, a fermented bacterial product that is labeled for use on many common garden pests. Use spinosad-based products only when bees are not active (early morning or late evening) and apply to the top and bottom of all leaves. Spinosad is a very safe option and is widely available at many local garden centers and nurseries.
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 tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
