Testing Biopesticides to Manage Crapemyrtle Bark Scale

Additional contributors to this article include: Dr. Rodrigo Diaz, Dr. Yan Chen, Dr. Blake Wilson, and Dr. Vinson Doyle.

Current crapemyrtle bark scale management methods depend heavily on pesticides, which can have a negative impact on beneficial insects. Biopesticides, insecticides that are developed from live organisms, have shown potential for managing several pests and have low impact on non-target insects and other organisms. The objectives of this research were to determine (1) if biopesticides can be used as a management tool to suppress crapemyrtle bark scale in different seasons, and (2) effects towards beneficial lady beetles known to attack crapemyrtle bark scale.

For those interested, here as some details as to how we designed our trial. Treatments were applied as a bark spray to potted plants or full-grown trees infested with crapemyrtle bark scale during winter, spring, and fall 2019. The fungal biopesticides Ancora® (Isaria fumosorosea strain PFR97) and BioCeres® (Beauveria bassiana strain ANT-03), and bacterial biopesticides Venerate® (Burkholderia spp. A396 strain) and Grandevo® (Chromobacterium subtsugae PRAA4-1T strain) failed to control crapemyrtle bark scale in greenhouse conditions. When BioCeres®, Ancora®, and BotaniGard® (B. bassiana strain GHA) were delivered in field settings, BioCeres® significantly increased ratio of dead to total scales on full grown trees in the winter trial; whereas BotaniGard® was more effective during the fall trial on small potted plants. In the spring trial, biopesticides failed to control crapemyrtle bark scale. Temperature impacted product efficacy in the field. According to our laboratory studies, higher fungal germination was achieved at 82°F, and higher germination rates were between 77 and 86°F. Therefore, products containing B. bassiana can be a good management tool for crapemyrtle bark scale during cooler temperatures.

Impact of the biopesticides on the natural enemies was assessed in laboratory conditions by dipping the insects in a biopesticide mixture and observing survival over time. BotaniGard® significantly reduced the survival of larvae and adults of both Hyperaspis bigeminata and Chilocorus spp., both beneficial lady beetles that feed on crapemyrtle bark scale, by at least 57%. Adults of Chilocorus spp. had longevity also reduced by 40% when treated with BioCeres®; and Ancora® reduced the survival of H. bigeminata larvae by 69%. When lady beetles were collected from an area sprayed with biopesticides, entomopathogenic fungi spores were collected from their bodies, ensuring contact but not disease in realistic conditions.

In conclusion, my research has shown that biopesticides should be considered as a management tool to enhance scale mortality and could be used in integration with other management techniques in the landscape. Results of this project provided a basic understanding of the impact of biopesticides for the management of crapemyrtle bark scale. However, we can still learn a lot by conducting additional research on efficacy of different B. bassiana strains and product formulations to suppress crapemyrtle bark scale.