Agriculture, Ecosystems and Environment 79 2000 215–231
Drift control and buffer zones for helicopter spraying of bracken Pteridium aquilinum
R.C. Robinson
a,∗
, R.G. Parsons
b
, G. Barbe
c
, P.T. Patel
d
, S. Murphy
e
a
International Application Technology Group, Rhône-Poulenc, North Newbald, York YO43 4TY, UK
b
Aldhams Experimental Farm, Rhône-Poulenc Agriculture Ltd., Lawford, Manningtree, Essex CO11 2NF, UK
c
1, Rue du Lac, 92500, Rueil Malmaison, France
d
Environmental Sciences Department, Rhône-Poulenc Agriculture Ltd., Ongar Research Station, Ongar Essex CM5 OHW, UK
e
Silsoe College, Cranfield University, Beds, MK45 4DT, UK Received 22 March 1999; received in revised form 20 December 1999; accepted 21 December 1999
Abstract
Application of asulam herbicide by helicopter, as a primary treatment of bracken, requires appropriate buffer zones to protect non-target plants, conservation areas and water catchments from spray drift. Drift from large-scale applications of
asulam were monitored at two moorland sites where helicopters were fitted with Delavan RD ‘Raindrop’ drift-reducing, hollow-cone nozzles. Drift was measured on 10 m vertical ‘strings’ and on flat cards at intervals to 200 m downwind. Potted
seedlings of Rumex acetosa, as a bioassay, were exposed over similar distances.
At 200 m downwind, levels of drift were close to limits of detection by high performance liquid chromatography HPLC. With wind speeds at the legal limit for helicopter spraying, total drift fallout integrated to 1 km downwind accounted for
0.61 of the applied asulam. In these conditions, fallout dropped below 1 of the applied dose rate approximately 35 m downwind of the sprayed area. In general terms, beyond 15 m from the sprayed areas, drift levels from the helicopters proved
similar to those reported from tractor-operated boom-sprayers. Bioassay data correlated with asulam fallout. A zero-effect level of 100 g ha
− 1
after 7 weeks 2.25 of the dose for bracken eradication suggested a buffer zone of 15 m which might be doubled to 30 m to allow for inaccurate flying, late shut-off, dosage errors and species with greater sensitivity than Rumex. On
the basis of this work, and also to protect private water abstractions, the Environment Agency approved a 50 m buffer zone for helicopters fitted exclusively with RD Raindrop nozzles. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Bracken; Pteridium aquilinum; Asulam; Helicopter spraying; Drift; Buffer zones; Rumex acetosa; UK
1. Introduction
The systemic herbicide asulam, methyl4-amino- benzenesulphonylcarbamate, is applied by helicopter
as a primary treatment of larger, often inaccessible, stands of bracken. To assess the environmental risks
∗
Corresponding author. Tel.: +44-01430-827747; fax: +44-01430-827729.
E-mail address: roderick.robinsonaventis.com R.C. Robinson
from such work, drift-monitoring studies were car- ried out by Marrs and Frost 1996, using a Rumex
acetosa Common Sorrel bioassay, which suggested the need for a 160 m buffer zone to protect suscepti-
ble, non-target species. This was subsequently applied without qualification wherever there were perceived
risks of drift onto non-target plants, conservation ar- eas or water-courses extracted for drinking purposes.
Delavan RD Raindrop nozzles Tate, 1977 can re- duce drift, increase spray recovery Bouse et al., 1976
0167-880900 – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 0 0 0 0 1 2 7 - 4
216 R.C. Robinson et al. Agriculture, Ecosystems and Environment 79 2000 215–231
and enhance the efficacy of asulam applied aerially to bracken Horsnail and Robinson, 1984; Robinson,
1984. The pertinent work by Marrs and Frost, how- ever, had evaluated drift for helicopters which were not
set-up exclusively with RD nozzles. When this mea- sure is adopted under commercial conditions, bracken,
itself sensitive to asulam, rarely shows a response beyond a few metres downwind of the boom ends.
Missed-strips sometimes arise which reflect a sharp edge to the sprayed swath and an absence of high lev-
els of drift which would otherwise assist swath match- ing. It was therefore suspected that the 160 m buffer
zone was too restrictive of helicopter spraying in many areas where invasive bracken required control, espe-
cially in upland localities intersected by numerous water-courses.
Recognising these factors, a protocol was approved by the Environment Agency England and Wales to
demonstrate, through further monitoring, that a re- duced buffer-zone was feasible when helicopters were
fitted exclusively with RD Raindrop nozzles. The protocol called for monitoring of commercial-scale
spraying of typical upland bracken, again using a R. acetosa bioassay to compare with the work of Marrs
and Frost. Drift of asulam itself was to be mea- sured using high performance liquid chromatography
HPLC methods to avoid debate over use of tracers. Drift fallout on sampling cards was to be measured
to correlate bioassay data with dosage. Airborne drift was also to be monitored on vertical ‘strings’ to
permit comparison with other, definitive drift studies.
Such studies Wilson, 1995 have indicated that drift-reduction nozzles used on helicopters can de-
crease drift to levels comparable with conventional tractor-operated boom spraying. Where such compa-
rability may be demonstrated, interpretation of limited assay data and the choice of buffer zones required can
be resolved by the widely-accepted agricultural prac- tice pertaining to tractor-drawn sprayers. Part of this
study therefore undertook such a comparison based on the data of Lloyd and Bell 1983.
2. Materials and methods
