National Plant Board
Impact of Rootball Dips on White Grub Survival
Impact of Root Ball Dips on White Grub Survival 1
Catharine M. Mannion, David G. Nielsen, Michael G. Klein, and Win McLane
Tennessee and Ohio
Nature of Work: Japanese beetles are a significant threat to the profitability of nurseries. Currently,individual state quarantines require treatment or production practice-based certification for nursery stock originating in infested areas before plants are exported to uninfested areas. The following states maintain exterior quarantines or other certification requirements for Japanese beetle: Arizona, Arkansas, California, Idaho, Kansas, Minnesota, Missouri, Nevada, Oregon, Utah, Washington, and Wisconsin (1). Dipping root balls of one foot diameter or less in insecticides is currently used by some nurseries as a method to eliminate white grubs, but there is little scientific evaluation of the efficacy of this method on larger rootstock. In 1995, Nielsen and Klein (2) found that 15 to 18 inch lilac and witch hazel root balls dipped in Dursban TI and 50WP for 30 seconds significantly reduced white grub survival. Additional research is necessary to determine the effect of soil type, root ball size, and the duration of dipping on the efficacy of dipping. Therefore, a collaborative study among researchers at Tennessee State University, The Ohio State University – OARDC, USDA – ARS, and USDA – APHIS was conducted to examine the efficacy of chemical dip treatments of 24 and 32 inch root balls, from two soil types, dipped for three different time periods, on control of white grubs.
Trees were selected from three different nurseries in Ohio. Selection was based on previous sampling for white grubs to insure a natural infestation of larvae in the root balls. Two sites were in northern Ohio where the soil was sandy and well-drained. Trees selected from these two sites included magnolia, ash, linden, and maple. Most of the grubs found from these root balls were Oriental beetle (81%), followed by European chafer (9%), Asiatic garden beetle (8%), and Japanese beetle (2%). The third site was located in southern Ohio where the soil was heavy (clay) and poorly drained. All the trees selected there were Sargent crabapple. Japanese beetle was the dominant grub (79%) followed by masked chafer (21%).
Trees from all locations were transferred to one site for dipping. Treatments included Dursban 50WP at 2 lb ai/100 gallons, Dursban 4E at 2 lb ai/100 gallons, and Oftanol 2F at 0.2 lb ai/100 gallons and at 0.4 lb ai/100 gallons. Root balls were dipped for 1, 2, and 5 minutes in each of the chemical treatments. The control trees were dipped in water 1, 2, and 5 minutes. There were 4 single-tree replications for each chemical-dip time combination. Both 24 and 32 inch root balls from northern Ohio (sandy soil) and only 24 inch root balls from southern Ohio (clay soil) were dipped. At the time of dipping, root ball temperatures ranged from 32 to 43oF and the ambient temperature remained below 50oF. All trees were transported to Wooster, Ohio, one week after dipping. The root balls were evaluated five weeks after dipping. All the soil within each root ball was thoroughly examined for the presence of white grubs. The number of live and dead grubs were documented and the live grubs were identified. Additional trees that were dipped and subsequently planted are currently being evaluated for phytotoxicity. The data were transformed (log X+1) and subjected to analysis of variance. Means were separated with Tukeys multiple range test (3).
Results and Discussion: Overall, insecticide treatments reduced the number of live grubs compared to the control treatment (Table 1). Dead and decaying grubs were found in all insecticide treatments. Dipping for a minimum of 2 minutes with either insecticide gave the best results. The 5-minute dip performed similarly to the 2-minute dip. Insecticide treatments were essentially similar regardless of root ball size and soil type. Dursban 4E performed slightly better than Dursban 50WP and both rates of Oftanol 2F. The fewest number of live grubs were most consistently found in root balls dipped in Dursban 4E.
Dipping root balls can be an expensive and “messy” method of controlling white grubs, but it can be a reasonably effective regulatory treatment. The results of this study indicate that dipping root balls can be a viable method to use for eliminating grubs. Further research may allow for “fine-tuning” application rates and dip duration with reference to soil type, root ball size, and phytotoxicity.
Significance to Industry: Although it is not suggested that dipping root balls be the primary method of grub control, it can potentially be used as a “last resort” effort if a nursery wants to undertake the expense and potential hazards in working with large quantities of insecticide. These data demonstrate that this method can be efficacious against white grubs.
- American Association of Nurserymen. 1995. Federal & State Quarantine Summaries.
- Nielsen, D. G. and M. G. Klein. 1996. Efficacy of root ball dips for controlling white grubs. Proceedings of the 1996 Annual Japanese Beetle Review, McMinnville, TN.
- Abacus Concepts. 1987. Statview II. Abacus Concepts, Berkeley, CA.
1This article reports results of research only. Mention of a proprietary product does not constitute an endorsement or a recommendation for its use.
Table 1. The effect of dipping root balls in insecticide on larval (grub) survival.
(lb ai/100 gal)
1 Means followed by different letters are significantly different (P<0.05; ANOVA)