Spray behaviour and efficacy of herbicides and fungicides applied to wheat at reduced volumes

Abstract

Timing is a key component of maximising the efficacy of pesticide sprays and therefore of reducing inputs relating to the production of arable crops.  Timeliness is a function of work rate and the ability to make applications in as wide a range of conditions as possible.  For a boom sprayer, work rate is mainly a function of spraying speed, boom width and application volume, particularly as filling the sprayer takes quite a long time.  Studies have shown that reducing volumes from 200 to 100 L/ha can typically increase work rates by 30%.  However, reduced volume applications may mean reduced efficacy and, with conventional nozzle systems, increased drift.  While drift control has been addressed by application methods, such as nozzle design and the use of air assistance, questions relating to efficacy remain, particularly when using drift reducing application systems.  This project aimed to identify acceptable limits for reducing application volumes and provide information to assist users in determining application methods appropriate for use with reduced application volumes.

Studies to characterise the delivery systems that can be used to make low volume applications used laboratory and field experiments to examine deposits on artificial vertical and horizontal target surfaces.  The results showed that coverage on both target types was a function of application volume rather than delivery system.  Reducing volumes increased the variability in deposits with all delivery systems and some systems increased the deposit on vertical targets as volumes were reduced.  Large droplets from air induction nozzles gave greater variability in target deposits at all application volumes.

Field trials applying a T2 fungicide to winter wheat showed no significant differences between different application systems.  Disease control and yield were better at 50 and 100 L/ha than at 25 and 200 L/ha, although differences at the higher volumes were not statistically significant.  There was some indication that high forward speeds and low application volumes may reduce efficacy.