Some of the terms used to describe the effectiveness and side effects of spray application include:
| Field Crops | Tree and Bush Crops |
High volume (HV) | >600 | >1000 |
Medium volume (MV) | 200-600 | 500-1000 |
Low volume (LV) | 50-200 | 200-500 |
Very-low volume (VLV) | 5-50 | 50-200 |
Ultra-low volume (ULV) | <5* | <50 |
* VARs of 0.25 – 2 l/ha are typical for aerial ULV application to forest or |
The next table shows the theoretical coverage on plants if monodispersed droplets (i.e., all droplets have the same diameter) in these size classes were to be evenly applied at the lower limits of the ultra-low, very-low, low, medium, and high VAR ranges for field crops. It assumes that all droplets were captured and retained, and the leaf area index is 1.
% Cover (per ha) for lower limits of VAR classes: | ||||||||||||||
|
| ULV | VLV | LV | MV | HV | ||||||||
Mono-dispersed Droplet Size | Cross sectional area of deposit (m2)* | droplets per m2 | 1 | 5 | 50 | 200 | 600 | |||||||
10 | 3.1 x 10-10 | 190,985,932 | 6 | 30 | NR | NR | NR | |||||||
50 | 7.9 x 10-9 | 1,527,887 | 1.2 | 6 | 60 | NR | NR | |||||||
75 | 1.8 x 10-8 | 452,707 | 0.8 | 4 | 40 | NR | NR | |||||||
100 | 3.1 x 10-8 | 190,986 | 0.6 | 3 | 30 | 120 | NR | |||||||
150 | 7.1 x 10-8 | 56,588 | 0.4 | 2 | 20 | 80 | NR | |||||||
300 | 2.8 x 10-7 | 7,074 | 0.2 | 1 | 10 | 40 | 120 | |||||||
500 | 7.9 x 10-7 | 1,528 | NR | 0.6 | 6 | 24 | 72 | |||||||
985 | 3.0 x 10-6 | 200 | NR | 0.3 | 3 | 12 | 37 |
*: single droplets, (spread factor taken as 2)
NR = not realistic spraying scenario (>100% cover represents coalescence of droplets).
“Per hectare” application often has very little relationship to the target area to be sprayed: leaf area indices of crops or weeds can range from fractions (pre-emergent weeds at the cotyledon stage) to >5 (late stage cereal crops). With bush and tree crops, VAR per hectare is even more inappropriate, and methods such as the unit canopy row system (UCR) have been developed where sprayer calibration is based on canopy size (Furness et al., 1998).
Surface run-off is another environmental issue, that is linked to endo-drift, and may account for substantial contamination of water courses, affecting drinking water quality. Amenity as well agricultural pesticide applications have been implicated, since run off is especially pronounced with treatments to hard surfaces, following rain.
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Furness, G.O., Magarey, P.A., Miller, P.H., Drew, H.J. 1998. Fruit tree and vine sprayer calibration based on canopy size and length of row: unit canopy row (UCR) method. Crop Protection, 17: 639-644.
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Himel, C.M. (1974) Analytical methodology in ULV. In: “Pesticide application by ULV methods” British Crop Protection Council Monograph No. 11, 112-119
Hislop E.C. (1987) Can we define and achieve optimum pesticide deposits? Aspects of Applied Biology, 14: 153-165.
Matthews, G.A. (2000) Pesticide Application Methods 3rd Edition. Blackwell Science, Oxford. 432 pages.
Matthews, G.A., Bateman, R.P. (2004) Classification criteria for Fog and Mist application of pesticides. Aspects of Applied Biology 71: 55-60
Parkin, C.S. (1992) Methods for measuring spray droplet sizes. In: Matthews, G.A. and Hislop E.C. (Eds.) (1993) Application technology for crop protection. CAB International, Wallingford, UK, pp. 57-84.
Spackmann, E., Barrie, I.A. (1982) Spray occasions determined from meterological data during the 1980-81 season at 15 stations in the UK and comparison with 1971-80. Meteorological Office Agricultural Memorandum No. 933. Meteorological Office, Bracknell, UK.
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