Amdro® Granular Insecticide (hydramethylnon) is an effective bait-formulated insecticide registered for use in landscapes and pastureland. New formulations of hydramethylnon have been developed, one incorporating the queen pheromone and another using a corn cob grit carrier. These new formulations were evaluated, along with a simultaneous application of Amdro plus fertilizer.
 

Materials and Methods

This trial was conducted in a pasture on the Look Ranch near Hempstead in Waller County, Texas. Thirty two plots, 0.5 acre squares were established, each containing a 0.2 acre circular sampling subplot area. Prior to treatment, the number of active mounds was documented for each subplot. Plots were arrayed from highest to lowest mound density and divided into four blocks (replicates). Treatments were assigned randomly within each block and included:

Treatment                                                    Rate_
1. Amdro® cob formulation                         5-6144 Batch 5-150 1 CW, applied 52.6 lb. per plot
2. Amdro®, experimental                             Lot# AC9902-94A, "Experimental Amdro", 1.5 lbs./acre
3. Amdro® + pheromone "med"                   Lot# AC9677-60, 0.5% Hyd + 0.01% pher., 1.5 lbs./acre
4. Amdro® + pheromone "high"                   Lot# AC9677-61, .73% Hyd + 0.01% pher., 1.5 lbs./acre
5. Amdro® standard                                    24567-08, 429101E, 1.5 lbs./acre
6. Urea + Amdro®                                      50 lbs. of 38%N urea + 1.5 lbs. Amdro/acre applied simultaneously
7. Urea                                                        50 lbs. of 38%N urea
8. untreated control                                       ---

Treatments were applied 8 and 9 August, 1995 using broadcast application equipment: the fertilizer in treatment 6 was applied with a PTO-driven fertilizer spreader. Treatments 2 through 4 were applied using a hand-held Cyclone 1C1 seeder, and Amdro in treatments 5 and 6 and the Amdro cob formulation in treatment 1 were applied using a Herd GT77 electric powered spreader.

Periodically following treatment, subplots were monitored for active ant mounds. Active mounds were rated on a scale from 1 to 5 (1 = 5 - 25 ants; 2 = 25-50 ants; 3 = 50 - 100 ants; 4 = "normal mound"; 5 = unusually large, active mound). Results were evaluated using analysis of variance (ANOVA) and means were separated using Tukey's Studentized Range Test (P < 0.05).
 

Results and Discussion

No significant differences were found between the performance of any of the experimental Amdro® formulations and the untreated control based on number of active mounds per 0.2 acre subplot area except during week 4 after treatment (Table 1). At that time, the experimental Amdro formulation performed numerically better than other treatments, but the addition of queen pheromone did not increase performance. Means from the cob formulation of Amdro and urea applied alone were not significantly different from the untreated control. Application of Amdro® simultaneous with fertilizer performed statistically as well as when applied alone.

Results of mound rating efforts documented treatment differences only on weeks 2 and 4 after application (Table 2). All Amdro®-based treatments performed similarly and had ratings significantly lower than those of untreated control plot mounds. Dry weather during the course of this trial suppressed ant activity in all plots. By 8 weeks after treatment, ant activity (in terms of number of active mounds per unit area) had returned to pre-count levels or higher (Table 1). The overall performance of Amdro in this trial was rather disappointing, with a maximum suppression of 74 percent 4 weeks after treatment.

 Table 1. Number of active red imported fire ant mounds before and after treatment using Amdro® (hydramethylnon) formulations, Look Ranch, Waller County, Texas, treated 8 and 9 August 1995.
 

^a Means followed by different letters are significantly different (P<0.05) using PC SAS, ANOVA and Tukey's Studentized Range test. Statistical analysis for 48 hr., 1 and 2 week evaluations did not include Amdro cob formulation and the two urea treatments.

  Table 2. Ratings of active red imported fire ant mounds following treatment using Amdro® (hydramethylnon) formulations, Look Ranch, Waller County, Texas, treated 8 and 9 August 1995.
 

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