Evaluation of sprayer systems for applying agro-chemicals to cereal crops

Abstract

Part I
Summary

In the first three years of the project, the performance of the Crop Tilter at 200 l/ha, a twin- fluid nozzle (Airtec) system at two pressure settings, a swirl nozzle (Country Workshops Superjet 100) and a flat fan nozzle all operating at 100 l/ha were compared with a reference flat fan sprayer operating at 200 l/ha. Laboratory measurements were made of droplet size and velocity distributions for each of the systems. Field studies examined spray deposit distributions, biological response and crop yield in randomised plot experiments. Spray droplets from the twin-fluid nozzle greater than some 120 µm were found to contain air inclusions such that the spray quality from this nozzle could not be classified using established techniques. The spray from the swirl nozzle had a smaller percentage of volume in droplets less than 100 µm in diameter compared with the flat fan nozzle operating at the same volume rate but vertical droplet velocities from this nozzle were substantially lower.

Spray drift from all the application systems was less than 3.5% of sprayer output when measured 8 m downwards of a single pass of the sprayer and in wind speeds of up to 25 km/h measured at a height of 2 m. Drift from the flat fan and drift from the cone nozzles operating at 100 l/ha were approximately equal but were double that from the reference flat fan system operating at 200 l/ha. The twin-fluid nozzle at 70-100 l/ha gave drift volumes equal to or less than the reference 200 l/ha system depending upon pressure settings. The crop Tilter also gave substantial drift reductions when compared with the reference system, mainly due to the reduced boom height with this system.

Results from the herbicide trials showed no significant differences between application methods in terms of weed control and crop yield, both at full and reduced dose rates.

Fungicide treatments of propiconazole or prochloraz plus fenpropidin or fenpropimorph were applied through each system at full and half dose rate at, or shortly after, full flag leaf emergence. Disease was assessed at the milky ripe growth stage and yield measurements taken. The standard 200 l/ha medium quality spray proved a reliable method of disease control but control was often equally good when sprays were applied through twin fluid nozzles, swirl nozzles or hydraulic nozzles at 100 l/ha, though it was sometimes impaired, particularly when fungicide doses were reduced.

The final two years of the project examined the performance of two air assisted "sleeve boom" sprayers. These were compared with the same conventional hydraulic nozzle system. Air flow characteristics both above and within the crop canopy were measured and differences found that were likely to modify deposition patterns within the crop canopy. In field trials to study the efficacy of herbicides and fungicides, the air-assisted and standard hydraulic nozzle systems were found to be equally effective and grain yields were not statistically different. Spray drift was significantly reduced with air-assisted sleeve-boom sprayers compared with fine hydraulic nozzles at 100 l/ha such that drift volumes were less than with the conventional 200 l/ha system. The velocity and direction of air-assistance was found to be a significant factor influencing spray behaviour.

The spray deposit measurements in the field trials indicated that there was some scope for manipulating deposit distribution patterns in the crop by adjusting the physical characteristics of the sprays and the conditions at delivery to the spray target. However, the differences between applications systems when averaged over a number of sites and growing seasons were not statistically significant. Differences in the physical characteristics and delivery of the spray from the application systems did give significant differences in the drift measured in both field and laboratory conditions. Measured spray deposits, however, were more variable reflecting the influence of crop structure and environmental conditions in the region of the crop canopy at the time of spray delivery. Where increases in deposit or changes in deposit distribution were achieved, differences between application systems were relatively small and did not result in statistically significant improvements in biological response or crop yield. Such changes could, however, improve the robustness of a chemical application.

The application systems studied (except the Crop Tilter) achieved the deposit levels and distribution patterns at a volume rate of 100 l/ha that were comparable with the standard flat fan hydraulic nozzle operating at 200 l/ha. Results from a computer model showed that this reduction in volume rate would improve the work rate of the sprayer by between 20 and 30% and would increase the opportunity for making a timely application. Improvements in timeliness may then provide scope for dose rate reductions providing that the level and distribution of spray deposits on the target surface is maintained at the lower volume rate. Further work is required to quantify the effects of timeliness and to determine the factors influencing crop canopy/spray interactions. Results from the work reported here also show the importance of drift control when using low volume rate application methods.

The need to control spray drift and minimise environmental and bystander contamination is now a part of the requirements of the Code of Practice for the use of agricultural and horticultural pesticides. The air-assisted, twin-fluid and Crop Tilter systems which gave good drift control in this study could give further improvements in timeliness if used in higher wind speed conditions than would be acceptable for comparable conventional spraying systems. This would require recognition within the Code of Practice that there is an acceptable level of drift and that the maximum allowable wind speed for safe sprayer operation is a function of the detailed design of the spraying system.

Part II.
Summary

Several spray application systems were tested for efficacy and deposition on barley or wheat crops over four seasons. A number of alternative jet types and spray qualities were studied in 1988 and 1989, then attention switched to air assisted spraying in 1990 and 1991. The application systems were used to apply herbicide and fungicide sprays, while applications of tracer materials allowed estimation of the rates and distributions of spray deposits.

Response to the herbicide treatments was fairly uniform except where the chemical rate was reduced. There was evidence of improved weed control from reduced dose herbicide sprays when air assistance was applied. Swirl (cone) jets also gave improved weed control from reduced dose treatments in a open, spring-sown crop.

Fungicide response, as measured by crop yield, was also fairly uniform. There are indications that applications on spring barley by a twin fluid nozzle in a 'medium' spray quality produced lower yield than applications by swirl jets. A small yield gain was evident from air assisted treatments on spring barley. Results from trials on winter wheat crops showed no consistent response.

Tracer tests on cereal crops at advanced growth stages revealed differing patterns of spray deposit at upper, middle and lower stem levels. This is accentuated on the lower stems, where swirl jets registered the lowest rate of deposition of the systems studied. Deposition on the lower parts of the stems was increased by air assistance applied to a 200 l/ha medium spray. Ground deposits from a 100 l/ha fine spray were reduced by air assistance when the spray bar was angled towards the rear, and spray distribution on the plants was biased towards the upper strata.