Herbicide Spray Drift Damage in the Merredin District Western Australia 1984, W.L.Smart
Department of Agriculture, Dryland Research Institute, Merredin, W.A. 6415.
“… Aerial Application. The most obvious inversion caused spray drift resulted from aerial application of Sprayseed (Paraquat/Diquat) 1 Litre ha-1 + 2,4-D Amine 500 ml + Spraying oil (1%) in 15 L ha-1 + Spraying oil (1%) in 15 L ha-1 water on a paddock at the top of a slope on 31st May, 1984. Air temperature was 20 degrees C, wind 5km hr-1 from the north east, and there were no clouds. Spraying was done from 3pm to 6pm. The night of 31st May/1st June was the coldest of that period, falling to 6 degrees C at Merredin. Spray damage covered 400 ha on two properties, north west of the sprayed paddock, and could be traced down slope from the site of application, through young crop and volunteer pasture and onto an extensive area of flat country where it flowed out as would water. There were no signs of Spray Seed droplet damage higher than 1.5m above ground. No trees were affected.
The largest area of damage caused by wind drift was also the result of aerial application of Sprayseed 1.5L ha-1 + 2,4-D Amines 500 ml ha -1 in 15 L ha -1 water. Spraying was done on a paddock near the top of a hill on the 2nd June, 1984, starting at 7am and finishing at noon. Wind was 4km hr-1 from the north east. There was no cloud, and the temperature was 18 degrees C. Sprayseed spotting could be seen on crop 4 km from the site of spraying, but eucalypt leaf spotting could be found 6.5km from sprayed paddock. Damage did not follow low lying country but moved up slope and down slope and moved directly down wind. Damage was also evident to the top of Eucalypt trees (15m), indicating a deep blanket of moving air carrying droplets. The area of damage (366ha) would have been greater had more crop been out of the ground.
Ground Spray Application
Boom spray drift was more common but usually involved smaller areas and did not cause leaf spotting on trees. The only large areas of boom spray drift covered 160 ha and 120 ha down wind of the application of SpraySeed in high winds. Other cases of boom spray caused drift ranged from 3 ha to 50 ha and in winds as light as 5 km hr -1 and water rates as high as 80 L ha -1 with most applications in the range of 30-40 L ha-1.
Damage caused by Roundup drift was investigated on four properties. 8 ha of wheat and 20 ha of lupins were re-sown.
Subsequent inspection of crops has shown that it is no longer possible to pick the effect of Sprayseed or Roundup drift damage. Harvest yield assessments may show the effect of spray drift damage…”