Thomas M. Wolf

Optimizing postemergence herbicide deposition and efficacy through application variables in no-till systems.

Abstract Laboratory experiments were conducted to determine the effects of application factors and standing Triticum aestivum stubble on herbicide spray deposition and efficacy in a simulated no-till environment. Spray deposition on weeds was reduced in the presence of stubble, and deposition losses on Amaranthus hybridus were greater than those on Setaria faberi. Spray penetration through stubble was significantly enhanced with electrostatic charging of a fine hydraulic spray. The combination of 45 kV electrostatic charge and 50 cm nozzle spacing produced maximum spray deposition on weeds and resulted in a 96% and 345% increase in deposition on A. hybridus and S. faberi, respectively, compared to the uncharged controls. Deposit reduction from standing stubble was greater at travel speeds of 16 km h−1 (36 to 52%) than 8 km h−1 (9 to 38%). On a dry weight and plant density basis, weeds retained more spray than was retained by stubble, yet stubble, at average densities, was capable of capturing 9 to 12% of total applied spray dose per unit area. Bounce studies of individual droplets of water or imazethapyr plus adjuvant mixture demonstrated that T. aestivum straw had a general affinity for all spray droplets, exhibiting no rebound even for 800-µm water droplets. Setaria faberi foliage exhibited poor retention of droplets: both 350- and 800-µm water droplets as well as 800-µm droplets of imazethapyr plus adjuvant mixture rebounded. Only 350-µm herbicide mixture droplets were retained by S. faberi. Amaranthus hybridus retained all droplets. In broadcast spraying, British Crop Protection Council “Medium” quality sprays were poorly retained by S. faberi compared to “Fine” sprays, whereas A. hybridus retained both sprays equally well. However, imazethapyr spray deposits resulting from coarser sprays were more efficacious on S. faberi than fine spray deposits, a difference that was not observed for A. hybridus. Nomenclature: Imazethapyr; metalaxyl, N-(2,6-dimethylphenyl)-N-(methoxyacetyl)alanine methyl ester; Triticum aestivum L., wheat; Amaranthus hybridus L. AMACH, smooth pigweed; Setaria faberi Herrm. SETFA, giant foxtail.

Screening of adjuvants for bioherbicide formulations with Colletotrichum spp. and Phoma spp.

Abstract A study was conducted to determine whether certain surfactants (Tween series: 20, 40, 80, and Tergitol NP series: 9, 10) and adjuvants (sorbitol and gelatin) would be useful components in bioherbicide formulations of Colletotrichum (10 isolates) and Phoma (5 islolates). The effect of adjuvants on conidial germination and mycelial growth varied with adjuvant, adjuvant concentration (0.01, 0.1, 1, and 5%), fungal isloates, and conidial density (105–108 conidia/ml). Tween 20 reduced germination and mycelial growth in some Phoma and all Colletotrichum isolates, whereas Tween 40 and Tween 80 stimulated germination without detrimental effects on mycelial growth of all isolates. Tween 40 and Tween 80 released conidia from self-inhibition of germination in Colletotrichum as compared to the germination of conidia at 107 conidia/ml in the absence of the adjuvant. Tergitol NP often reduced germination and mycelial growth. There were no trends in fungal responses to sorbitol. The responses of Colletotrichum were highly variable to gelatin, but for Phoma, gelatin increased germination and mycelial growth, and also released self-inhibition of germination. In summary, gelatin, Tween 40, and Tween 80 were useful components for bioherbicide formulations to increase conidial germination and mycelial growth of Phoma, whereas Tween 40 and Tween 80 were useful for Colletotrichum.

Spray Retention on Green Foxtail (Setaria viridis) and its Effect on Weed Control Efficacy by Pyricularia setariae1

The importance of spray retention to the biocontrol of green foxtail with Pyricularia setariae was characterized using airbrush and broadcast sprayers at variable application volumes. Spray retention was determined by measuring amounts of a tracer dye solution on treated plants using fluorescence spectrophotometry. Depending on the droplet size, broadcast spraying at 1,000 to 2,000 L/ha produced a level of retention equivalent to that of airbrush spraying until runoff. The trend of P. setariae spore retention on green foxtail was similar to that of liquid retention. Broadcasting P. setariae at volumes producing equivalent spray retention to that of airbrush inoculation resulted in a similar level of weed control under greenhouse conditions. Reducing broadcast volume from 2,000 to 250 L/ha lowered biocontrol efficacy only slightly, when the concentration of P. setariae was increased proportionally to keep the applied fungal dose the same. A nozzle with a fine droplet spectrum (volume median diameter [VMD] 207 μm) had a significantly greater retention efficiency than a coarse spray (VMD 325 μm), but this retention difference was not translated into consistent enhancement of biocontrol efficacy. Higher retention increases may be necessary for more substantial improvement in biocontrol of green foxtail by P. setariae. Nomenclature: Green foxtail, Setaria viridis (L.) Beauv. #3 SETVI; Pyricularia setariae Nisikado [synonym Pyricularia grisea (Cooke) Sacc.]. Additional index words: Application volume, biocontrol, droplet size, mycoherbicide. Abbreviations: AAFC, Agriculture and Agri-Food Canada; AAV, actual application volume; VMD, volume median diameter.

Contribution of aerosols generated during mixing and loading of pesticides to operator inhalation exposure.

The occupational exposure resulting from the application of crop protection agents continues to be of great interest for the purposes of identifying hazards or determining safer chemical handling methods. The purpose of the present study was to identify the potential respirator exposure of a mixer/loader to chlorothalonil, with the mixing and loading operation as the only source of aerosols (particles <13 microm diameter). Three worst-case mixing/loading scenarios were simulated in the lab: (1) a spill of undiluted chlorothalonil formulation onto a dry, horizontal metal surface; (2) a spill of undiluted chlorothalonil formulation onto a rapidly rotating shaft; and (3) pouring undiluted chlorothalonil formulation into a container of water. Aerosol generation from these scenarios was compared to that resulting from atomizing dilute chlorothalonil through hydraulic nozzles. Aerosols were captured with a cascade impactor, and quantified by gas chromatography. Results indicated that simulated spill scenarios generated aerosol concentrations between 2.1 and 5.3 ng/l, which were in the same order of magnitude as, and only marginally higher than, the detection threshold (1.7 ng/l) and background levels (2.2 ng/l). In comparison, atomization of dilute chlorothalonil through a hollow cone and flat fan nozzles resulted in airborne concentrations of 354 and 96 ng/l, respectively, related to the atomization characteristics of these nozzles. Measurement of the dimensions of the aerosol cloud indicated that aerosols resulting from a spill amounted to approximately 10(-5)% of the spilled chlorothalonil. It was estimated that a male worker respiring 29 l/min would inhale approximately 0.32-0.78 ng of chlorothalonil during a typical 30 s spill, assuming a 1% transfer efficiency between the spill site and the mixer/loader. These estimates were between 10000 and 480000 times less than literature data for respiratory exposure of chlorothalonil by applicators and harvesters, suggesting that inhalation of aerosols from mixing and loading represents a minor component of overall exposure.

Effect of spraying adjuvants with the biocontrol fungus Microsphaeropsis ochracea at different water volumes on the colonization of apple leaves

Abstract In a previous study, it was observed that Microsphaeropsis ochracea was less efficacious as a biofungicide for apple scab when applied under field conditions as an unformulated spore suspension with an airblast spray using low water volumes as compared to a ground cover spray using high water volumes. The effect of spore concentration (109 to 1012 spores ha−1), water volume (250–1500 L ha−1), and 20 adjuvants were studied to improve colonization of apple leaves by M. ochracea. Using commercial-type spray equipment, the fungus was applied to excised apple leaves. Higher spores concentrations resulted in greater colonization. Water volume did not have a strong impact on colonization. Only a few adjuvants improved germination (glycerine) and mycelial growth (K-90, Agrimer, Ekol, and Tween 80) in some trials. When tested on apple trees, the adjuvant Assist provided the most consistent improvement in colonization in five out of eight trials. The use of oils, humectants, and surfactants could broaden the opportunities for using this biofungicide.

Use of nozzle-induced air-entrainment to reduce active ingredient requirements for pest control

Abstract A simple nozzle design/modification is presented which takes advantage of the known effect of the increasing biological efficacy of a pesticide with decreasing drop size for insecticides and perhaps fungicides. However, applying active ingredient (AI) in unassisted fine sprays leads to poor canopy penetration and increased drift hazard. Therefore, the air entrained by medium-coarse nozzles spraying water is utilised to impart kinetic energy to a finer spray containing AI. A fine nozzle is sprayed into a medium-coarse spray at an angle of approximately 15 ° from vertical approximately 10 cm below the medium-coarse nozzle, spraying into the direction of travel of the sprayer. The subsequent spray cloud consists of: small drops, typically The atomisation characteristics and potential drift problems of such a nozzle system were investigated. The results show that the velocity characteristics of the carrier (medium) spray were imparted to the fine spray, removing the problem of low spray cloud kinetic energy. Coalescence of drops in-flight was approximately 50%. Drift measurements in a large wind tunnel showed that drift increased four-fold at 4 m/s windspeed and approximately two-fold at 2 m/s. Taking into account the expected reduction in AI requirements, at 2 m/s, drift was quantitatively approximately the same as that of the medium nozzle.

The application of biological pesticides: Limitations and a practical solution

Biopesticides and agrichemicals are applied using basically the same equipment. The limitations imposed on biological or conventional chemical pesticides by current application systems are discussed. In general, any pesticide must be applied into a crop using the commonly used application system in that crop. This will normally be the hydraulic nozzle. Researchers attempting to increase the efficacy of a biopesticide by changing application system should bear in mind the constraints set by farmers on altering their usual spraying practices. These constraints are considered along with the criteria required for the successful market introduction of a novel application system. A novel application system, the “double nozzle” is introduced, which fulfils the criteria discussed, in particular the reduction in terms of amount of active ingredient required for pest control. The scientific rationale for this new system is explained, and its performance discussed.RésuméEn principe, biopesticides et produits agrochimiques sont pulvérisés à l’aide du même équipement. Les limitations imposées aux pesticides biologiques aussi bien qu’aux produits chimiques conventionnels par les systèmes d’application couramment utilisés sont discutées. Quels que soient les pesticides utilisés, ils seront généralement appliqués sur une certaine culture à l’aide du même matériel d’épandage, le plus communément employé pour ce type de culture, c’est-à-dire normalement des buses hydrauliques. Les chercheurs qui tentent d’augmenter l’efficacité d’un biopesticide en modifiant le système de pulvérisation devraient garder à l’esprit les réticences des cultivateurs à l’égard de tout changement dans leurs pratiques d’épandage. Ces contraintes sont examinées en détail, ainsi que les critères requis pour commercialiser avec succès tout nouveau système d’application. Un système nouveau de pulvérisation appelé la ’double buse’ est présenté, lequel satisfait aux critères discutés ci-dessus, en particulier en termes de réduction des quantités d’ingrédients actifs utilisés pour lutter contre les nuisibles. Les arguments scientifiques qui plaident en faveur de ce nouveau système sont expliqués et ses performances discutées

Spray retention for liquid and mycoherbicide inoculum in three weed-biocontrol systems

Abstract Spray retention is often used to measure herbicide delivery to optimize application parameters, but little is known about retention characteristics of mycoherbicide inoculum applied for weed biocontrol. This study examined inoculum retention of three mycoherbicide agents, Pyricularia setariae, Colletotrichum truncatum and C. gloeosporioides f. sp. malvae, on their respective weed targets: green foxtail, scentless chamomile and round-leaved mallow. Conidium suspensions of these fungal pathogens containing a sodium-fluorescein tracer dye were applied at 500, 1000 and 2000 L ha−1 using a cabinet sprayer, and the liquid volume and number of conidia retained on the plants were quantified. On all three weed species, liquid and conidium retention showed a high degree of correlation at varying application volumes although slight differences existed depending on the weed species. Based on the analysis of regression slopes, liquid retention reflected conidium retention most closely on green foxtail but slightly overestimated the number on scentless chamomile and round-leaved mallow, possibly due to different plant morphology and spray run-off at extremely high application volumes. Liquid retention can generally be used as an indicator in studying effects of spray quality on mycoherbicide retention for improved delivery and biocontrol in these weed-biocontrol systems.

Response of four canola populations to ethametsulfuron

Abstract The effect of ethametsulfuron on populations of canola was evaluated in field and laboratory trials. Three canola populations (TR4, CB9604, and BC86-18) and the open-pollinated canola cv. ‘AC Parkland’ were treated with several doses of ethametsulfuron at the two- to four-leaf stage. In the field experiment, plant densities were determined before spraying and again at plant maturity. Density reductions during the growing season were observed for all populations (6 to 17%), but reductions due to ethametsulfuron above 0.3 g ha−1 depended on year, being noted for TR4 in 1997 (40 to 65%) only. In laboratory trials, only TR4 demonstrated sensitivity to ethametsulfuron, up to 49% visual damage averaged over all plants. The response was binary, with about 40% of plants at any given herbicide rate surviving unharmed and the remaining 60% of plants exhibiting > 90% visual damage. It is concluded that TR4 is sensitive to ethametsulfuron and further work, including a comprehensive genetic study, is required to determine the inheritance of sensitivity. Nomenclature: Ethametsulfuron; canola, Brassica rapa L.

Effect of MCPA and fenoxaprop on phytotoxicity, retention, foliar uptake and translocation of imazamethabenz in wild oat

Abstract The addition of MCPA (amine and ester) or fenoxaprop to imazamethabenz affected its phytotoxicity, retention and uptake and translocation in wild oat. MCPA amine and fenoxaprop, but not MCPA ester, antagonized the activity of imazamethabenz on wild oat. MCPA ester or fenoxaprop decreased, but MCPA amine had no effect on retention of imazamethabenz by wild oat foliage. Addition of MCPA ester increased absorption and acropetal translocation but decreased basipetal translocation of 14 C-imazamethabenz. Addition of MCPA amine had no effect on absorption, but decreased acropetal and basipetal translocation of 14 C-imazamethabenz. Fenoxaprop increased absorption and acropetal translocation, but decreased basipetal translocation of 14 C-imazamethabenz. Changes in absorption, translocation, or retention accounted for all observed changes in phytotoxicity.