N.M. Western

EFFECTS OF SOME AGRICULTURAL TANK-MIX ADJUVANTS ON THE DEPOSITION EFFICIENCY OF AQUEOUS SPRAYS ON FOLIAGE

Abstract The effects of 10 commercially available tank-mix adjuvants on the retention and coverage of aqueous sprays on foliage were examined quantitatively under track sprayer conditions, following application at their maximum recommended rates. Substantial enhancement of fluorescein retention was observed only on water-repellent barley and peas, but the differences in performance between the additives were considerable. Addition of the water-soluble tallow amine and nonylphenol surfactants gave the largest increases in retention, whereas there was little improvement in efficiency compared with water alone after inclusion of either the latex- or pinolene-based products or ammonium sulphate. Retention enhancement was also achieved using the mineral oil, vegetable oil, methylated vegetable oil and phospholipid ECs and the organosilicone surfactant, but this was often much less than that obtained for the water-soluble surfactants; the best EC was the methylated vegetable oil which also had the highest emulsifier content. Although spray quality was altered significantly in the presence of many of the adjuvants, modifications to this parameter alone could not account for changes observed in deposition efficiency, because retention enhancement was recorded in sprays with volume median diameters both smaller and larger than water. There was a better correlation between retention efficiency and the dynamic surface tension of the corresponding spray liquids, with the exception of the organosilicone, which, as expected from its high surface activity, gave essentially complete spray coverage on leaves. Nevertheless, good coverage could still be achieved by adding the two water-soluble surfactants, as well as the methylated vegetable oil and phospholipid ECs. Coverage performance of the other adjuvants tested was poor in comparison, reflecting, in part, their inferior retention enhancing properties.

Air-assisted spraying of arable crops, in relation to deposition, drift and pesticide performance.

Abstract Field experiments comparing spray deposition, spray drift and the biological efficacy of one herbicide and a number of fungicides in several crops treated by hydraulic nozzle sprayers and a novel air-assisted sprayer (Degania) are reported. Air-assisted sprays using fine-spray hollow-cone nozzles spaced at 25 cm were compared with coarser sprays applied at similar or greater volumes from standard hydraulic pressure nozzles. The quantity of spray deposited on different crop types was generally similar from both methods of application, but the uniformity of droplet distribution from the air-assisted system was usually superior. The air-assisted sprayer generally produced more drift than the standard sprayer. All spray methods generally produced similar biological results at full and half pesticide dose rates. A Brussels sprouts crop normally considered as being difficult to spray showed some biological benefits from air-assisted spraying.

Experimental air-assisted spraying of young cereal plants under controlled conditions

Abstract Cereal plants grown in trays outdoors were sprayed indoors, at the four-leaf stage, with and without air assistance from a commercial air-curtain device fitted with an electrically driven cross-flow fan. Flat-fan hydraulic pressure nozzles producing very fine/fine and medium spray qualities were fitted to the air duct so that they and the air curtain could be directed either 45 degrees forwards or 45 degrees backwards, relative to the direction of travel, as well as vertically downwards. Spraying was done at 0.5, 1.0 and 2.0 m s −1 and fluorescein deposits were measured on the plants and soil for all combinations of the above factors (36 spray options), each replicated three times. Analysis of deposits measured by spectro-fluorimetry showed that fine-quality sprays produced larger plant deposits than medium-quality sprays and that angling the spray trajectory, especially 45 degrees forwards, also substantially increased deposition. Forward angling was superior to the backward trajectory. Air assistance further increased the amount of spray retained, and reduced deposits on the soil. An increase in plant deposits of ∼74% was recorded for finer sprays angled forwards with air assistance compared with a medium-quality spray applied vertically without air assistance at a spray speed of 2 m s −1 . At the slowest spray speed (0.5 m s −1 ) both spray qualities angled forwards with air assistance increased deposition by ∼110% compared with a mean deposition increase of ∼75% without air assistance. Air assistance substantially reduced (∼70%) spray drift in a wind tunnel at a wind speed of 4 m s −1 , but significantly increased the small amounts of drift measured in winds of 1.0 and 2.0 m s −1 .

Experimental air-assisted spraying of a maturing cereal crop under controlled conditions

Abstract Outdoor tray-grown cereal plants at growth stage 39–41 were exposed to very fine/fine and medium-quality sprays from hydraulic flat-fan nozzles fitted to an air duct so that spray and air could be directed either 45 degrees forwards or vertically downwards. Spraying was done at 0.5 and 2.0 m s −1 and fluorescein deposits measured on plants and on the soil for all combinations of the above factors (24 spray options), each replicated three times. Finer sprays angled forwards and the use of air assistance interacted to increase total spray deposition on plants and reduce soil contamination. Fine sprays were better retained in the upper canopy and on stems. Forward angling increased deposits in the upper canopy but reduced penetration. A slower spray speed increased plant and soil deposition. Increasing amounts of air assistance improved plant deposits, especially in the upper canopy and on stems. Compared with ‘standard’ practice (a medium-quality spray, applied vertically downwards at 2 m s −1 , without air assistance), forward-angled air-assisted very fine/fine and medium-quality sprays increased plant deposits on whole tillers by ~71 and ~66% and reduced soil contamination by ~46 and ~66%, respectively.

Drift reduction and droplet-size in sprays containing adjuvant oil emulsions †

The droplet-sizes and drift produced by sprays containing dilute oil-in-water emulsions of various vegetable and mineral oil adjuvants were measured in wind-tunnel experiments. When compared with water or a surfactant solution, both types of oil adjuvant reduced the proportion of small driftable droplets and, hence, reduced measured spray drift. Vegetable oils were more effective at drift reduction than the mineral oil. Spray drift tended to increase with increasing oil concentration and decreasing emulsifier content.

Redistribution of foliar surface deposits of prochloraz by simulated rainfall and the control of eyespot disease of winter wheat

Abstract Outdoor-grown wheat plants sown in troughs and infected through indirect inoculation with the eyespot pathogen ( Pseudocercosporella herpotrichoides ) were sprayed with prochloraz in a spray chamber at Zadok GS 37. Prochloraz was applied in either low (151/ha) or normal (2001/ha) spray volumes to plants standing vertically or laid on their sides and masked to preclude spray deposition on the stem bases. After spraying, plants were kept in a glasshouse and a proportion were exposed to one or more light (0·4 mm total) or heavy (4·0 mm total) artificial rainfall regimens. Immediately after spraying with recommended amounts of fungicide, only traces were found on stem bases of plants sprayed vertically and, in the absence of rain, eyespot incidence was unaffected. Heavy rain applied one day after fungicide application redistributed from the foliage to the plant base c . 5·5 μg prochloraz/g stem tissue and decreased eyespot severity. Light rain redistributed less fungicide and had a smaller effect on eyespot. Spray volume had no effect on redistribution or disease control. The half-life of prochloraz on unweathered foliage was c . 6 days, but at the stem base, deposits changed little over two weeks.

Effects of some surfactants on foliar impaction and retention of monosize water droplets

The impaction and retention behavior of low-velocity (below 3 m s−1) monosize droplets (100–1000 μm diameter) containing either water or aqueous surfactant solutions was examined on wettable and water-repellant leaf surfaces using a high magnification video system. Mapping of bounce trajectories provided a history of droplet behaviour from first impact to final retention on, or escape from, a leaf, and yielded velocity thresholds for capture or bounce following impact of any droplet. Water droplets were captured on water-repellant leaves only when their pre-impact velocity fell below 0.25 m s−1, so that even small (120 μm) low-velocity (0.57 m s−1) droplets bounced between two and six times before finally being retained. Surfactant addition invariably reduced the number of bounces between first impact and retention, and increased the velocity threshold for capture following impact. The physical parameters of droplets, as expressed by Reynolds (Re) and Weber (We) numbers, are discussed and the trajectory data shown to generate two relationships between Re and We which define the transition from capture to bounce following impact. © 1999 Society of Chemical Industry

Experimental air-assisted electrohydrodynamic spraying

Abstract A linear electrohydrodynamic (EHD) atomizer, operated at −25 kV, was used to quantify the effects of droplet size, charge to mass ratio, forward speed and the addition of air assistance, on spray deposition in natural and artificial crop canopies. Spraying was done at 0.5, 1.0 and 2.0 m s−1 forward speed, using three Risella EL oil:butanol EHD formulations (80:20, 70:30 and 60:40) producing droplets with volume median diameters of ∼124, 71 and 48 μm and charge to mass ratios of ∼2.0, 7.5 and 9.5 mC kg−1, respectively. The two levels of air assistance used (11.3 m s−1, 0.39 m3 s−1 and 21.2 m s−1, 0.72 m3 s−1) were produced by a commercial air-curtain device. Spray deposition was compared with that obtained from medium-quality flat-fan hydraulic nozzles applying 238 1 ha−1 without air assistance. Spray drift was measured 2 m downwind over a winter wheat crop, in wind speeds of 1.5 and 2.5 m s−1. Using artificial targets, total spray deposition and canopy penetration from the charged sprays increased as target density decreased. Larger droplets with a smaller charge to mass ratio penetrated the canopy better than smaller, more highly charged sprays but gave poorer abaxial surface deposits. Air assistance increased canopy penetration but reduced abaxial surface deposits. In a winter wheat crop at growth stage (GS) 22, decreasing charge to mass ratio resulted in decreased plant deposits and increased ground contamination, although in all cases this was significantly less than that with hydraulic nozzle applications. Similar trends were measured at GS 37–39, where the addition of air assistance increased canopy penetration by highly charged sprays and decreased the soil contamination found with the larger-droplet, lower-charged applications. There was no consistent effect of forward speed. Spray drift from EHD sprays increased with increasing charge to mass ratio and decreasing droplet size, and was significantly greater than that from the hydraulic nozzle spray at both wind speeds. The use of air assistance reduced spray drift from the smallest droplets by ∼93%.

Mechanism of control of eyespot disease in winter wheat by the fungicide prochloraz

Abstract Winter wheat plants grown in troughs and infected with the eyespot pathogen ( Pseudocercosporella herpotrichoides ) were sprayed with prochloraz at growth stage (GS) 31 and 39 using a hydraulic nozzle sprayer and with a drop-leg spray system at GS 39. Some plants received artificial rain (4 mm) 1 or 4 days after spraying and were compared with those not receiving rain, with respect to foliar and stem-base fungicide deposits, as well as control of eyespot disease. Single pot-grown plants were treated topically with prochloraz inside the leaf axils and examined for redistribution of the fungicide by rain as well as the effect on eyespot disease. Rain redistributed the fungicide deposited by the hydraulic nozzle spray system from the initial site of deposition to the base of the crop at GS 31 and 39 and significantly suppressed eyespot disease development. No similar effects were found on the crop sprayed by the drop-leg system. The effect of rain on plants treated by topical placement of the fungicide in leaf axils was to redistribute prochloraz downwards between the outer leaf sheath and the stem, thus suppressing eyespot disease.