Barry K. Cooke

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.

Deposition and biological efficacy of a fungicide applied in charged and uncharged sprays in cereal crops

Abstract Barley and wheat crops were both sprayed at growth stages 30 and 61–75 with boom-mounted conventional hydraulic nozzles (250 l/ha), experimental hydraulic electrostatic nozzles (66 l/ha), electrically driven spinning discs (2 l/ha, oil-based sprays and 5 l/ha, aqueous spray) and ‘Electrodyn’ nozzles (1 and 2 l/ha, oil). The ULV spray systems (up to 5 l/haS) were used with or without air assistance. The distribution of both oil and aqueous sprays within the crops was measured with fluorescent tracers on plant parts and on whole plants. An experimental triazole fungicide (mixed with tracer) was applied to the crops by all the spray systems and the degree of control of leaf blotch (scald) caused by Rhynchosporium secalis (Oudem.) J.J. Davis in barley and mildew ( Erysiphe graminis DC) in wheat compared with the deposit data. The two highest-volume spray systems gave similar results for disease control and there was no significant difference between the charged and uncharged sprays at 66 l/ha. The Micron Ulva spinning disc and ‘Electrodyn’ systems with air assistance also performed well. Unassisted ULV sprays were often unevenly distributed within the crops and gave inferior disease control. The ‘Electrodyn’ system often produced large total deposits relative to other spray systems but unassisted sprays were mainly deposited on the upper plant parts. The results indicate that application at volumes as low as 1 l/h can be as biologically effective as conventional high-volume spraying, when compared at the same dose rate of fungicide (90 g/ha). Relationships between spray distribution within cereals and the sites for pest and disease attack are discussed with regard to different methods of application.

Physical, chemical and biological appraisal of alternative spray techniques in cereals

Abstract In a multidisciplinary study, spinning disc, rotary cage, electrostatic aqueous and electrodynamic methods of atomization were compared with conventional systems based on various types of flat-fan hydraulic-pressure nozzles commonly used in farm practice. The 80-degree type hydraulic nozzles at 200 l/ha rate produced the largest proportion of droples greater than 350 μm whereas the 110-degree type at the same rate produced the largest quantity of droplets below 50 μm. The effects of electrostatic charging on droplet spectra of aqueous sprays was slight at 200 l/ha rate but at 70 l/ha the proportion by volume of both the largest and smallest droplets was significantly reduced. The rotary cage atomizers produced a droplet spectrum of intermediate width whereas the spinning disc and electrodynamic systems yielded the narrowest spectra. In terms of tracer deposition, the hydraulic nozzles (especially the 110-degree type) used at about 200 l/ha produced the most even partitioning of spray within the crop and yielded the lowest coefficients of variation (CV) of mean deposits both on cereal plant parts and on weeds. The rotary cage, spinning disc and ‘Electrodyn’ either yielded high CV values or lacked penetration into the crop structure. In barley at an early growth stage (GS 31), there was little effect on tracer deposition by electrostatic charging of aqueous sprays, whereas at GS 57 charging at the 70 l/ha rate increased deposition in the upper plant parts. The hydraulic nozzle systems (especially the 110-degree type) were generally the most effective for weed and disease control and produced the highest grain yields from fungicide applications. All methods of spraying, however, produced a significant yield gain from fungicide applications.

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 .

Relationships between the herbicidal activity and foliar uptake of surfactant-containing solutions of glyphosate applied to foliage of oats and field beans

Abstract The enhancement effects of a C 13 /C 14 series of aliphatic alcohol (A) surfactants on the herbicidal activity of glyphosate-(monoisopropylammonium) were examined using a model formulation system that enabled relative performance to be assessed at equivalent spray deposition rates. Surfactants with mean molar ethylene oxide (E) contents of 11, 15 and 20 were more effective in increasing glyphosate activity against oats ( Avena sativa L.) than AE6, when the herbicide was sprayed at 54 or 108 g acid equivalent (a.e.) ha −1 . At the lower herbicide dose, these surfactants, when added at 1 and 5 g I −1 caused ∼70% more reduction in foliage weight than the herbicide alone, compared with a ∼50% greater reduction at 0.2 g l −1 . However, there was no significant concentration effect on enhancement with the same three surfactants at the higher herbicide dose. On field bean ( Vicia faba L.), surfactant E content had little influence on herbicide enhancement compared with surfactant concentration. This effect was noticeable only with glyphosate at 54 g a.e. ha −1 , with the highest surfactant concentration (5 g l −1 ) inducing a ∼35% greater reduction in foliage weight than herbicide without surfactant. At the higher glyphosate rate there were only modest improvements in efficacy on this species after surfactant addition. Results obtained from experiments using 0.2 μl droplet applications of formulations containing [ 14 C]glyphosate at herbicide (0.35 and 0.7 g l −1 ) and surfactant concentrations equivalent to those of the spray solutions, showed that the corresponding enhancements in uptake and translocation of the radiolabel correlated well with the observed improvements of herbicidal activity on oats but not on field bean. On both species, AE6 was antagonistic to uptake of radiolabelled herbicide. Increased herbicide absorption or biological activity did not appear to be related to the spreading properties of the surfactant-containing formulations on the two target surfaces. The implications of these findings are discussed with reference to the problems of predicting and optimizing the performance of agrochemical formulations with surfactant adjuvants.

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.

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.