Growing media is the major source of damaging population of Systena frontalis (Coleoptera: Chrysomelidae) in ornamental plant nurseries.

Systena frontalis (F.) (Coleoptera: Chrysomelidae) is a serious pest of ornamental shrubs in containerized ornamental plant nurseries in the central and eastern United States. Adult S. frontalis cause numerous shot holes on foliage, rendering ornamental plants unmarketable. Growing media in plant containers is an overwintering site of S. frontalis, but the extent to which adults emerging from the growing media can damage the plants is unclear. Experiments were conducted on panicled hydrangea (Hydrangea paniculata Siebold) in Georgia, North Carolina, and Virginia nurseries in the spring of 2021 and 2022 to answer this question. The treatments were (i) canopy caged, (ii) whole-plant caged, and (iii) noncaged hydrangea plants. In all 3 states, beetle abundance and feeding damage found on caged (whole plant) and noncaged plants were significantly greater than those on plants where only the canopy was caged. In most sites and years, beetle abundance and feeding damage were not significantly different between the noncaged plants and those where the canopy and containers were caged, suggesting that the majority of S. frontalis emerged from the growing media and the majority of damage suffered by the hydrangea plants were caused by beetles emerging from the containers. Because growing media contributed to a significant proportion of the S. frontalis population in a nursery, treatment targeting larvae in the growing media should be a critical component of a holistic management plan against S. frontalis.