Assessing a program for post emergent control of problem weeds in cotton using shielded sprayers
Shielded sprayers have been widely and quickly adopted by cotton growers for weed control
in the inter-row. In the last three seasons, the increase in area sown to RoundUp Ready®
cotton has been a major contributor to this because the label directions of RoundUp Ready
Herbicide® specifys the use of shielded sprayers when growing RoundUp Ready® cotton.
After the 2001/02 season, growers reported yield losses up to 30% after using shielded
sprayers. It is thought that leakage of spray was the probable cause of this yield loss. The
Cotton Research and Development Corporation (CRDC) provided funding to both
Conservation Farmers Inc (CFI) and The Centre for Pesticide Application and Safety (CPAS),
School of Agronomy and Horticulture, The University of Queensland, Gatton Campus to
undertake studies to determine the major factors causing herbicide leakage from shields and
to develop strategies that would reduce potential yield loss, but not affect weed control.
Both CFI and CPAS have collaborated in a number of trials to maximise resources. This
document highlights preliminary wind tunnel (laboratory) and field research on the influence of
shield height, wind speed (travel speed), nozzle selection (spray quality), boll retention and
herbicide efficacy. In a one year study there is no scope to confirm experimental
observations, and therefore all results should be seen as preliminary outcomes.