Question
My viburnum has been eaten by aphids all summer, even after regular spraying with insecticidal soap. What can I do to save it? The leaves are 80% eaten. Will it survive?
Answer
I don’t think it’s aphids that are to blame, but rather the Viburnum leaf beetle (Pyrrhalta viburni). Aphids suck the sap from plants and can eventually cause leaves to turn yellow and fall off, but they don’t make holes in the leaves. Aphids may be present, however, and are always more visible than galleroot, since they don’t try to hide, giving you the impression that they’re the culprits.
The Viburnum leaf beetle, an elongated beetle accidentally imported from Europe, on the other hand, drops to the ground when it sees you and can therefore go unnoticed. It can actually skeletonize leaves, leaving them in tatters. It mainly attacks snowball viburnum (Viburnum opulus ‘Roseum’), but can also damage other viburnums, notably our native American Cranberrybush (V. trilobum). The plant rarely dies after a first defoliation, but if they are repeated annually, it does.
Controlling Viburnum Leaf Beetle
The easiest way to control Viburnum leaf beetle is with BTT (Bacillus thuringiensis var. tenebrionis), sold to commercial potato growers to eliminate Colorado potato beetles. Unfortunately, this pesticide, although organic and perfectly safe (it’s a bacterium that only affects beetles), is not yet registered for domestic use and therefore not available unless you know an understanding potato grower. After a single treatment, the insect stops eating and dies a few days later… and as it dies, its body releases other bacteria that will affect the next generation.
Other treatments are more demanding: we suggest picking them up by hand or stirring infested branches over a bucket of soapy water (soapy water is toxic to insects). Insecticidal soap would not be effective on its own, but with the addition of a little pyrethrin, yes. Some products contain both. Treatment would be more effective in early summer, when the larvae are young, than now, when the damage is being done by adults. You should also be aware that pyrethrin, even if organic, is still toxic and must be used with great care.
Finally, sometimes the easiest solution is to pull out the plant causing the problem and replace it with one that doesn’t have insect or disease problems.
Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil on September 11, 2005.
I bought the native viburnum 5 years ago two feet tall. First year it was all eaten by the beatle. Second year it was half eaten, third year a third eaten. Now its a huge full of berries very healthy shrub. Lovely in the garden. It can be pruned to any size, as I have kept it at 4 feet tall. It is a native very resilient life giving shrub. Do not waste your money or time, I did nothing mother nature does not need us. Let it go. Do make sure to water it and compost for the first two years. I will be planting a few more this year along with the nanny berry, native Aronia, New Jersey Tea, and a few others if I can find the space. There is always something that will eat your garden and that is a sign of a healthy garden. More native plants less baby sitting, watering and weeding.
BTK is available in Canada for consumers to use. I bought some 2 years ago and it is still on the market. It is the treatment of choice for boxtree moths.
Maybe it will work on this beetle?
If you do nothing but wait for many many years as was done here in Center Montville, Maine, there will be plenty of song birds migrating through and staying for food. Finally, you will have very few beetles and fruit on the Viburnums. Thanks for your fine articles. (Sorry, pensioner, no funds.)