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.

Strategies and tactics for herbicide use reduction in field crops in Canada: A review

“…Factors affecting herbicide performance include nozzle type, nozzle angle, droplet size, nozzle spacing, travel speed, and electrostatic charging of herbicide sprays (Wolf et al 2000;Kudsk and Streibig 2003). There is often a tradeoff between herbicide efficacy and drift (Wolf 2002;Kudsk and Streibig 2003).…”

“…Adjusting application variables increased herbicide deposition on weeds in a simulated notill environment (Wolf et al 2000). However, application variables often impact herbicide efficacy in a species-specific manner (Wolf et al 2000), and this may limit implementation of improvements in application technology depending on the weed species composition of individual fields.…”

Towards the optimisation of Coarse sprays to reduce drift and improve efficacy in Australian cropping systems

“…Poorly distributed sprays in a crop canopy reduce the effectiveness of a spray application (Uk and Courshee 1982;Wolf et al 2000), which can cause growers and applicators to have to reapply their sprays to achieve adequate pest control. Post-emergence herbicide efficacy is directly related to the ability to penetrate through crop canopies (Knoche 1994).…”

“…When sprayers are properly calibrated the likelihood of the need for further application will be reduced (Uk and Courshee 1982). Improving coverage increases the pesticide dose on each plant in most cases to maximise the efficacy of a plant protection product (Knoche 1994;Wolf et al 2000). Selecting the best nozzles and application parameters requires the use of quantifiable methods to understand differences in application parameters .…”

“…To minimise losses of pesticide during an application, improved spatial distribution of sprays in a plant canopy is critical (Law 2001). Sprays that are not well distributed through a crop canopy reduce the overall efficacy and effectiveness of the application (Uk and Courshee 1982;Wolf et al 2000), which can cause growers and applicators to have to reapply their sprays to achieve adequate insect pest control. Effectiveness of a spray also depends on the availability of a pesticide as it can be applied at the wrong time or applied to parts of the plant where insects are not present (Courshee 1960).…”