December found me exploring the plant collections of two public gardens where I suspected the presence of Virburnum Leaf Beetle egg laying sites on Viburnum dentatum var venosum and Viburnum dentatum. The presence of the beetle in southeastern PA is not new having been confirmed in many but the most southeastern of counties previously, but it was a new pest in each of these locations. My suspicions were confirmed by PSU entomologists.
Now is the perfect time to go out and scout your Viburnums for this pest. According to research done at Cornell University, more than chemical control, the mechanical control of pruning off these egg laying sites on the branch tips is the best way to regulate this non-native pest.
Seems these small beetles prefer our native Viburnums to the non-native species, most frequently found on Arrowwood (Viburnum dentatum) and American Cranberrybush (Viburnum opulus var americanum) to name a couple. Once a significant component of our native forest understory, native viburnum populations are in decline due, in great part, to deer browse and competition from escaped non-native species. This beetle is just another challenge native viburnums and those who manage natural areas are facing.
You can help control this pest by examining all the viburnums you see. Look at the tips of the branches, the adult prefers to lay eggs in the newest growth of the year. You will see small brown and black rough areas in a line. This is an indicator of presence of viburnum leaf beetle. Once positively identified, remove the egg site using proper pruning techniques and destroy all the cuttings you have made.
Viburnums typically bloom on one-year old wood and are normally pruned immediately following bloom, if needed. In this case, to save the shrub and the surrounding population of shrubs, you may have to sacrifice this year’s blooms by removing the flowering wood anytime between October and April. While this may mean less flowers this year, this will help ensure you have removed the eggs before the larva emerge in late April saving the shrub to bloom for years to come.
So head on out on a crisp winter day with your hand-lens and your pruners and help to stop the spread of this pest threatening native and ornamental populations of these beautiful and valuable spring blooming shrubs.
Bucks Horticulture 