PEST UPDATE : Snowball Aphid
By Tawny Siminsky , Extension Entomologist , UMass Extension Landscape , Nursery & Urban Forestry Program
Snowball aphid Neoceruraphis viburnicola is capable of causing severe leaf curling damage to Viburnum opulus , V . opulus ‘ Roseum ’ ( formerly ‘ Sterilis ’), V . acerifolium and V . prunifolium . Certain other species of viburnum , on the other hand , appear to be resistant to this insect ( such as Viburnum plicatum f . tomentosum ). The snowball aphid causes twisting of foliage early in the spring by feeding on plant fluids with piercing-sucking mouthparts .
[ This spring ] in Massachusetts , the damage from these insects is very noticeable and anecdotally seems more pronounced in some locations . Like many aphids , the snowball aphid has a complex lifecycle , part of which is unfortunately still unknown to science . While viburnum are primarily impacted , snowball aphids also have a secondary host plant whose identity is yet unknown .
Viburum is the host on which this insect overwinters , after the aphids lay their eggs on the twigs and buds in the fall . The egg stage overwinters , and hatches while buds begin to open in the spring . The young , developing aphids will feed at the buds in the spring . As the aphids mature , they reach approximately 2.5 mm . ( 1 / 10 inch ) in size and may be bluish-white in color , their bodies appearing as if they ’ ve been dusted in powdered sugar . The mature , asexual stem mothers of this species produce a large number of offspring without mating . Approximately two months following egg hatch , the progeny of the stem mothers leave the viburnum , but it is unclear where they go . By September , they return as a migrant form of aphid ( to the viburnum ) and give birth to the sexual forms of the species that produce the overwintering eggs . While snowball aphid is not found on viburnum year-round *, the leaf-curl damage from this insect can last beyond the time when the aphids are physically present .
The damage seen on viburnum from the native snowball aphid is not reversible with chemical management this season . Some professionals and homeowners may choose to prune severely distorted plants if the level of aesthetic damage is currently unacceptable , and the damage is localized on specific branches . Remember that any remaining aphids found in the curled leaves will be protected from contact insecticide applications . Viburnums that are in bloom should not be treated with systemic insecticides for the protection of pollinators .
Snowball aphid damage ( PC : Swanson )
For next season : If you have viburnum species ( such as those listed above ) that are highly susceptible to this insect and frequently attacked , you may consider replanting with a resistant species if that makes sense for the landscape . Dormant oil applications may also be made on susceptible plants just prior to budbreak when temperatures and weather conditions allow . Target the buds and twigs for overwintering eggs with these applications . ❖
* Note that there is another species of aphid ( Aphis viburniphila ) which is noted in the literature to have a year-round association with Viburnum spp .; yet this insect does not cause leaf distortion .
Reprinted from UMass Hort Notes June 2021 .
MLP Newsline | Winter 2021 7