White grub management in turfgrass relies overwhelmingly on preventive insecticides with repeated yearly applications. Our research reveals that under this scenario the role of natural enemies as egg predators is compromised by early-season intervention. Their beneficial role, however, could be conserved with later season intervention.
Overall, the ecological costs of pest management practices are more difficult to gauge than economic and environmental costs. Until exposed, however, the relevance of nontarget effects cannot be included in cost-benefit analyses. Therefore, the balance between intended and unintended impacts should be explicitly examined as one additional way to inform pest management decisions. Until then, we are motivated to select, develop, and promote reduced-risk approaches for the management of turf-infesting insect pests. As made accessible through extension programming, this information will lead to more rational pesticide use across the extensive turfgrass habitats managed in the U.S. Northeast.
impact statement issue
There are more than 35 million acres of turfgrass in the United States, in the form of lawns, golf courses, athletic fields, parks, and other recreational areas. In New York alone, 3.4 million acres were maintained as turf in 2003, with maintenance expenses exceeding $5.1 billion. Across these extensive, diverse, and high-value systems, decision-making strategies are required for the management of pests and diseases.
This is especially relevant to white grub control in home lawns, which represents the major insect pest complex in one of the most extensive and expanding components of our urban and rural landscape. At present, white grub control scenarios in turfgrass of the Northeast have essentially closed the door to best integrated pest management because of reliance on long-residual preventive insecticides. The ideal application window at the time of egg laying means that scouting cannot be conducted, and that thresholds cannot be assessed. As a consequence, there is no nonarbitrary way to decide not to intervene from one season to the next, and this leads to unnecessary applications of insecticides.
An explicit assessment of the balance between intended target effects and unintended nontarget effects should be investigated, especially in perennial systems such as turfgrass where beneficial arthropods may have an enhanced role in promoting ecological stability.
impact statement response
In previous studies with white grub control options like trichlorfon and halofenozide, only imidacloprid harbored discernible nontarget impacts on the abundance of soil-active invertebrates in turfgrass. Repeated preventive applications reduced populations of certain nontarget taxa and this persisted over all six years of applications. Springtails, which can be beneficial for thatch degradation, were 2.6 times more abundant without imidacloprid. Predaceous beetles, which can be beneficial for regulating populations of pest insects, were 4.1 times more abundant.
Because nontarget impacts are an inevitable consequence of almost all control tactics, we moved on to address whether declines in the abundance of nontarget fauna actually compromised any of their beneficial functional roles. In other words, is the magnitude of decline in abundance relevant to turfgrass health?
Our approach was to examine the impact of single applications of imidacloprid and related neonicotinoid insecticides on the predation of Japanese beetle eggs as one measure of the biocontrol services provided by soil arthropod communities. Egg removal declined 28 to 76 percent in plots treated with insecticide. Effects were detected as early as one week after applications and persisted as long as four weeks after application. The impacts were similar across imidacloprid, clothianidin, dinotefuran, and thiamethoxam.
Neonicotinoid application at the time of beetle oviposition puts intended effects (mortality of neonates) in conflict with unintended effects (disruption of egg predation). The conservation of predation on early life stages might buffer the reduced efficacy of late-season applications that target more advanced instars. As application timing and post-application irrigation affect insecticide performance, they might also be manipulated to reduce nontarget effects.
impact statement summary
Every pest management tactic will have nontarget effects. The more salient question is whether those impacts are relevant to agroecosystem health and sustainability. We showed previously that applications of a widely used insecticide can suppress the abundance of certain nontarget soil arthropods in home lawns. To build on that, we examined whether those impacts actually harbor functional consequences for turfgrass habitats.
Biocontrol services in the form of predation of Japanese beetle eggs were significantly disrupted by applications of long-residual neonicotinoid insecticides. Intervention with insecticides at the time of egg hatch thereby puts intended effects (mortality of young grubs) in direct conflict with unintended effects (disruption of egg predation). Refining our understanding of the balance between the intended and unintended consequences of reliance on preventive insecticides will enhance opportunities for pest management practitioners to harness the benefits of their beneficials.
