Horseradish Leaf Bioassays, 1989

Abstract

Abstract Single plots 4 rows wide by 25 ft long with 36-inch centers and 24-inch plant spacing were marked off within a field of ‘Swiss’ horseradish in Madison Co., Illinois. Bond adjuvant was used in all spray applications, including the check, except for one Ambush treatment. Treatments were applied 11 Sep with 3 hollow cone nozzles (TXSS-8)/row from a 4-row sprayer delivering 30.8 gal/acre at 50 psi and 2 mph; the entire field had been treated with a fungicide by the grower earlier that day for white rust prevention. Air-dried foliage (15 leaves per treatment) was returned to the laboratory in Champaign and refrigerated overnight. On 12 Sep, 3 leaf pieces (2 square inches each) were cut from 5 leaves/treatment, mixed together, and assigned in groups of 3 to glass petri dishes containing moistened filter paper and 8 larvae (mostly third instars, from a 1988 colony established with collections from horseradish fields in southwestern Illinois). Treatments were replicated 5 times for a total of 40 larvae/treatment. Replicates were held at 80° day: 75°F night and 14L:10D. Mortality (no movement following gentle probing) was assessed cumulatively at 24-h intervals for 72 h.