Allow beneficial insects to rid nasturtiums of aphid infestation naturally
Question: My nasturtiums have been absolutely beautiful this year. I grew the trailing kind, and they're tumbling over my retaining wall. But, last week, I noticed some of the leaves are turning yellow. When I examined them, I discovered an infestation of tiny bugs underneath some of the leaves. I think they're aphids. What can I do to get rid of them? I don't want to spray any chemicals because of my son.
Answer: Unfortunately, aphids are a very common pest of nasturtiums. They're particularly problematic if the plants have been fed with a nitrogen-rich fertilizer or manure.
Aphids are attracted to the lush, succulent foliage growth generated by excessive nitrogen, so it's best to grow aphid-prone plants, such as nasturtiums, in “leaner,” unfertilized soils.
Sometimes it's a tough balance between having enough nutrition to sustain the plant, but not having so much that you promote pest issues. This is one of the reasons why I suggest fertilizing annual and perennial gardens with compost only, rather than using any granular or liquid fertilizers.
The good news is that, if you garden organically, you won't need to do anything about those aphids. Gardens that are not regularly blanketed with nonselective chemical pesticides have a rich population of beneficial insects that will come to your rescue and naturally reduce the aphid population before they can do much damage.
Yes, you may lose a nasturtium leaf or two while you wait for the good bugs to arrive, but these beneficial insects will eventually strike a nice balance and limit the aphids on their own. And, by letting them do their thing, you'll be encouraging future generations of these pest-munching beneficial insects to take up residence in your garden.
Spraying your nasturtiums with insecticidal soap, horticultural oil or even a sharp stream of water from the hose will remove a food source for beneficial insects and may actually harm the good insects themselves, reducing future populations and encouraging subsequent pest outbreaks.
Inspect the infested nasturtium leaves every now and then and look for signs of predation. You're likely to find ladybugs and their larvae, lacewing larvae, spined soldier bugs and lots of other beneficial insects feeding on the aphids.
You also may spot “aphid mummies.” These brown, swollen aphids have been parasitized by a tiny, nonstinging parasitic wasp that's not much bigger than a gnat. Inside the body of these “mummy” aphids a larval parasitic wasp is growing. Eventually, it will pupate, emerge as an adult and go on to parasitize and eliminate more aphids.
When you kill the aphids, it destroys the natural balance between good bugs and bad bugs that Mother Nature has perfected for millennia.
I suggest you do as I do and monitor the aphids on your nasturtiums, watching for signs of nature at work.
In all the years I've been gardening, I've never once lost any plant to an aphid infestation. Instead of worrying about it, I say have a glass of wine and let the good bugs do their thing.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com.
Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., Third Floor, D.L. Clark Building, Pittsburgh, PA 15212.
