The Impact of Spray Droplet Size on the Efficacy of 2,4-D, Atrazine, Chlorimuron-Methyl, Dicamba, Glufosinate, and Saflufenacil

Abstract

Herbicide applications often do not reach their full potential because only a small amount of the active ingredients reaches the intended targets. Selecting the appropriate application parameters and equipment can allow for improved efficacy. The objective of this research was to evaluate the effect of droplet size on efficacy of six commonly used herbicides. Atrazine (1.12 kg ai ha−1), cloransulam-methyl (0.18 g ai ha−1), dicamba (0.14 kg ae ha−1), glufosinate (0.59 kg ai ha−1), saflufenacil (12.48 g ai ha−1), and 2,4-D (0.20 kg ae ha−1) were applied to seven plant species using an XR11003 nozzle at 138, 276, and 414 kPa and a AI11003 nozzle at 207, 345, and 483 kPa. Each herbicide, nozzle, and pressure combination was evaluated for droplet size spectra. Treatments were applied at 131 L ha−1to common lambsquarters, common sunflower, shattercane, soybean, tomato, velvetleaf, and volunteer corn. Control from 2,4-D was observed to increase approximately 12% on average for all species except common lambsquarters as droplet size increased from medium to very coarse (Dv0.5303 to 462 μm;Dv0.5is droplet size such that 50% of spray volume is contained in droplets of equal or smaller size). Control with atrazine was near 95% for common lambsquarters, common sunflower, and soybean. Atrazine provided the greatest shattercane control using a medium (Dv0.5325 μm) droplet, whereas the same droplet size provided the lowest tomato control. Control of common lambsquarters, shattercane, and tomato with cloransulam-methyl increased 79% when decreasing droplet size from extremely coarse to fine (Dv0.5637 to 228 μm). Dicamba control of common lambsquarters increased 17% using a medium droplet compared with a fine droplet (Dv0.5279 to 204 μm). Dry weight of common sunflower and soybean was reduced 21% using dicamba when using a very coarse spray compared with a fine spray classification (Dv0.5491 to 204 μm). Common lambsquarters control using glufosinate increased 18% using a fine spray classification (Dv0.5186 μm) compared with medium (Dv0.5250 μm) and both very coarse droplet sizes (Dv0.5470 and 516 μm). Conversely, tomato and velvetleaf control with glufosinate was maximized using a very coarse (Dv0.5470 and 516 μm) or extremely coarse droplet (Dv0.5628 μm) with increases of 11 and 25% compared with a fine spray (Dv0.5186 μm). Saflufenacil control of volunteer corn was 38% greater using extremely coarse droplets (Dv0.5622 μm) than fine, medium, and very coarse spray classifications (Dv0.5257 to 514 μm). Overall, spray classifications for the herbicides evaluated play an important role in herbicide efficacy and should be tailored to the herbicide being used and the targeted weed species.

Spray droplet size and carrier volume effect on dicamba and glufosinate efficacy

“…However, this result shows that even with a systemic, synthetic auxin herbicide there is a critical droplet size at which weed control is lost, especially at low carrier volumes. Previous research identified decreases in weed control as droplet size increased for other systemic, synthetic auxin herbicides, but this trend was not previously observed for dicamba …”

“…Previous research identified decreases in weed control as droplet size increased for other systemic, synthetic auxin herbicides, 20,21 but this trend was not previously observed for dicamba. 29 For 187 L ha −1 , the droplet size at which maximum weed control was predicted for dicamba was 900 μm (Ultra Coarse) and 150 μm (Fine) for the mortality proportion and weed dry biomass per plant response variables, respectively. The loss in weed control across the range of droplet sizes for the weed dry biomass per plant response variable was minimal as 90% of maximum weed control was achieved with a 900 μm droplet indicating the greater carrier volume buffered the droplet size effect.…”

“…Additionally, no losses in herbicide efficacy as droplet size increased were observed for several contact herbicides . The impacts of droplet size on herbicide efficacy are convoluted, and each herbicide and weed species interaction requires a tailored approached to maximize efficacy …”

“…27,28 The impacts of droplet size on herbicide efficacy are convoluted, and each herbicide and weed species interaction requires a tailored approached to maximize efficacy. 29 In addition to droplet size, carrier volume plays a crucial role in herbicide coverage and efficacy. 30 Generally, across herbicides, efficacy decreased as carrier volume decreased.…”

Dicamba drift as affected by nozzle type, wind speed and spray composition

“…Specifically for dicamba, Creech et al (2016) observed a 17% better control of common lambsquarter using medium droplets compared with fine droplets. Besides providing safer applications, larger droplets may also provide better efficacy in some situations.…”