Last updated 6/19/98 |
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Timothy J. Gibb
A relatively new product, Naturalis-T, a fungal pathogen, has become available for use against certain insect pests in turfgrass environments. The impact of this material on beneficial turfgrass dwelling invertebrates, however, is unknown.
Many beneficial invertebrates (ground beetles, earthworms, spiders and ants) reside in nearly every stand of turfgrass. Recent studies have demonstrated the importance of these naturally occurring beneficial invertebrates to turfgrass management. Little thought, however, has been given to the impact of applications of new pesticides, on these beneficial organisms.
Naturalis-T was applied to 100 sq. meter plots of turfgrass on July 2, 9, 16, 23 and 30. Treatments were applied in a randomized complete block fashion and were replicated 5 times. Dry pitfall traps were placed in the center of each treated plot. Arthropods collected were extracted alive, contained individually and returned to the laboratory for testing. Each arthropod was contained individually until death, surface washed with a .1% Triton X solution and placed dry on ODA at room temperature for 7 days to determine presence of Beauveria bassiana. Earthworms were field collected and contained in bins to determine whether infection could occur with caged worms. Earthworms were divided among eight plastic bins containing 1 gallon of finely tilled soil (4 inches deep). Half of the bins were covered with turfgrass (1/4 thatch) to more closely approximate natural field conditions. Weekly treatments of Naturalis-T were applied at label rates to each of the bins. Two earthworms per bin were extracted each week after treatment, surface washed with a 0.1% Triton X solution and placed on ODA at room temperature for 7 days to determine presence of Beauveria bassiana. Ant populations were sampled 15 times throughout the growing season. Sample methods consisted of tuna baited subterranean traps made from microcentrifuge tubes inserted into the soil within the center 16 square meters of each plot. Eight traps were used per plot. Traps were retrieved after 24 hours and ant species present were identified. Number of ant positives (ants collected in microcentrifuge tubes) per plot were transformed using arcsin/ sq. rt. transformations to allow statistical analyses to be generated. Numbers were compared to determine long term treatment impact on ant populations.
- No apparent turfgrass phytotoxicity nor differences in turf vigor were noted between any treatments.
- Neither earthworms, spiders or ground beetles were found to be infected by Naturalis-T in any of the screenings that we performed.
- Ants of the genera Solonopsis, Lasius and Tetramorium, all were found to be susceptible to the fungus.
- Ant populations, monitored over the growing season to determine the effects of weekly applications of Naturalis-T were unable to show that the fungus detrimentally affected the ant populations or colonies over the course of the growing season.
This experiment indicates that earthworms, spiders and ground beetles are not highly susceptible to applications of Naturalis-T. Ants, though individually susceptible, do not appear to re-infect their colony.
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