A comparison of two ultra-low-volume spray nozzle systems by using a multiple swath scenario for the aerial application of fenthion against adult mosquitoes.

Two hydraulic spray nozzle systems, a flat fan and a high-pressure hollow cone, were used for ultra-low-volume application of the mosquito adulticide fenthion under a multiple swath scheme. Eight swaths at 322-m intervals were applied from a height of 91 m to simulate operational conditions. Deposition, effects on nontarget organisms (fiddler crabs), aerial flux, and mosquito (Ochlerotatus taeniorhynchus) mortality were monitored for 8,230 m downwind, including the area under all 8 swaths. The flat-fan nozzle system deposited 88 times the amount of fenthion deposited by the high-pressure system in a lightly vegetated zone directly beneath the application area (0-2,134 m). Further downwind (2,286-4,420 m) in the 2nd semiopen urban zone, 10.5 times more chemical was deposited with the flat-fan nozzles than with the high-pressure nozzles, and in the 3rd highly vegetated zone (4,572-8,230 m), 25 times more was deposited compared with high-pressure nozzles. The corresponding nontarget mortalities with the flat-fan nozzle were 80, 12, and 17% at 2,438, 3,658, and 4,572 m, respectively. No treatment-induced mortality was observed with high-pressure nozzles. Similar amounts of fenthion residue were recovered from yarn samples for both nozzle systems, with the exception of the zone directly under the flight paths, where the flat-fan system deposited 2.5 times the amount recovered with the high-pressure system. Mosquito mortality was similar between the 2 nozzle types except in the farthest zone, where the average mortalities for the high-pressure system and the flat-fan system were 73.4 and 34.8%, respectively. Regression analysis of the mosquito mortality and yarn samples showed that the high-pressure hollow-cone application could control mosquitoes with half the amount of chemical compared to flat-fan nozzles.

A comparison of two spray nozzle systems used to aerially apply the ultra-low-volume adulticide fenthion.

Field experiments with the mosquito adulticide fenthion (Baytex) compared the conventional flat-fan nozzle system (Tee Jet 8002SS) and a new high-pressure hollow-cone nozzle system (1/8 MISS). Ground deposition and aerial flux of the mosquito adulticide fenthion were measured up to 4.83 km downwind by using filter paper and yarn collectors, respectively. Biological efficacy was investigated by using caged salt-marsh mosquitoes (Ochlerotatus taeniorhynchus), and caged fiddler crabs (Uca pugilator) were exposed to quantify nontarget impact. Peak deposits to the ground were 1,729 microg/m2 and 240 microg/m2 for the flat-fan nozzles and high-pressure cones, respectively. Deposits from the flat-fan nozzles resulted in a cumulative fiddler crab mortality of 80%, whereas no deaths were recorded with the high-pressure system. The range of fenthion flux detected in the air when using the yarn collectors was similar for the 2 systems, with both showing drift through 4.83 km. For the flat-fan spray nozzle system, the aerosol flux ranged from 3.02 to 67.33 microg/yarn collector. The range of aerosol flux for the high-pressure nozzle spray system was 0.15-50.66 microg/yarn collector. Although the 2 systems produced comparable ranges of flux, the high-pressure system provided higher control efficacy against mosquitoes. Maximum mosquito control when using the flat-fan spray nozzle system against female salt-marsh mosquitoes was 26.6%, whereas maximum control with the high-pressure spray system was 92.9%.

Ground deposition impact of aerially applied fenthion on the fiddler crabs, Uca pugilator.

Caged fiddler crabs, Uca pugilator, were exposed to field ULV applications to measure the impact of fenthion. Two nozzle systems, conventional flat-fan nozzles (Tee Jet 8002SS) and high-pressure hydraulic nozzles (1/8 MIS), were compared using single spray swaths. Fenthion residues were detected throughout the 4.83-km test zone for both systems. Heavy ground deposits (650-1,670 microg/m2) of fenthion were found within 1 km using the flat-fan nozzle systems, which resulted in 80% fiddler crab mortality. Less than 100 microg/m2 fenthion ground deposits were detected during the high-pressure nozzle trials. No fiddler crab mortality was observed within the first 1-km zone following 3 single swath applications repeated during 3 consecutive nights. We found also that when the fiddler crabs were exposed to 700-800 microg/m2 fenthion, mortality occurred. Significant crab mortality (>50%) was observed when residues exceeded 1,000 microg/m2.