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Defining the size of target for air induction nozzles

Project Report No. 317

Defining the size of targets for air induction nozzles

by

P.C.H. Miller1, E.S. Powell2, J.H. Orson2, P. Kudsk3 and S. Mathiassen3

1Silsoe Research Institute, Wrest Park, Silsoe, Bedford, MK45 4HS
2Morely Research Centre, Morley St. Botolph, Wymondham, Norfolk, NR18 9DB
3Danish Institute of Agricultural Science, Flakkebjerg, Slagelse, Denmark

 

Abstract

The use of air induction nozzles on boom sprayers applying sprays to arable crops has become an established way of achieving high levels of drift control. Such nozzles create a spray with relatively large sized droplets that have air inclusions within the droplets such that they behave differently from droplets created with conventional nozzles. Because the droplets are large there are fewer of them and there is then the potential for small targets such as weeds at early stages of growth to receive an inadequate dose or coverage to give good control. This study measured the droplet size distributions produced by a range of air induction nozzles operating with tank mixes typical of those used to treat both grass and broad-leaved weeds. Nozzles were then selected for use in pot and field trials that gave sprays with large, medium and small relative droplet size distributions for this type of nozzle.

Field trials were conducted over two seasons in which the level of control of both a grass (black-grass) and a broad-leaved weed species (common field-speedwell - second year only) were assessed when sprayed with the different air induction nozzles at a range of doses and timing of applications. The field studies were supported by experiments in which comparable treatments of foliar-acting herbicides were applied to outdoor grown pot plants of a range of target weed species at different stages of growth using the same air induction nozzles. Results from the pot studies were analysed in terms of ED90 doses for each weed/nozzle/growth stage combination and were used to support the interpretation of the field trial data.

Results of the work showed:
• air induction nozzles with the same specification but from different manufacturers/suppliers gave different droplet size distributions particularly when spraying water or water plus a surfactant;
• operation with typical tank mixes reduced the differences between droplet size distributions from different commercial versions of the same air induction nozzle specifications although there were still significant differences between different versions;
• air induction nozzles gave lower levels of efficacy when compared with applications from conventional nozzle designs with the greatest reductions in efficacy coming from applications with air induction nozzles producing the largest droplet size distributions: greater reductions in efficacy were generally observed in the pot experiments than in the field trials;
• for the grass weed target, the highest levels of efficacy were observed at the 2-3 leaf stage rather than at the one leaf stage;

It was concluded that air induction nozzles provide a good method of achieving drift control but with some risk to efficacy on small targets with foliar-acting herbicides. This risk can be reduced by using air induction nozzles that create a relatively small mean droplet size and by treating grass weed targets at the 2-3 leaf stage.

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