Fading process of herbicidal droplets amended with emulsifiable spray adjuvants on cucurbitaceae leaves

Authors: LIN, JENG-LIANG - National Chiayi University; Zhu, Heping

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2019
Publication Date: 2/1/2019
Citation: Lin, J., Zhu, H. 2019. Fading process of herbicidal droplets amended with emulsifiable spray adjuvants on cucurbitaceae leaves. Transactions of the ASABE. 61(6):1881-1888. https://doi.org/10.13031/trans.13061.
DOI: https://doi.org/10.13031/trans.13061

Interpretive Summary: Herbicide efficacy is often correlated with droplet reactions including droplet coverage area and fading time on weed surfaces, and it may be reduced if the active ingredients in droplets do not uniformly spread out and remain on the surfaces. This is especially true for the difficult-to-wet weeds which are managed with recommendations by adding surfactants into herbicidal spray solutions. In this research, surfactants containing anti-evaporation agents, paraffinic oil, non-ionic surfactants, and bio-degradable compounds were investigated for their effects on the coverage area and fading time of droplets deposited on cucurbitaceae leaves. These spray adjuvants were mixed in two commonly used herbicides. Compared to herbicide-only solution, the maximal coverage area was considerably increased by addition of the oil adjuvants containing paraffinic oil and non-ionic alkoxylated alcohol but not by addition of the water emulsifiable spray adjuvant containing hydro-treated naphthenic mineral oil. Also, addition of water emulsifiable spraying oil surfactants in herbicidal spray solutions did not significantly affect the fading time. Thus, these investigations would instruct spray applicators, weed control specialists, and adjuvant and herbicide formulators that active ingredients are critical components in surfactants when selecting proper surfactants as additives in spray solutions to maximize weed control efficiency and minimize herbicide use.

Technical Abstract: Coverage areas and fading times were investigated for herbicidal droplets with and without emulsifiable surfactants deposited on cucurbitaceae leaves. Experimental parameters included 250 and 450 µm sessile droplets tested at 30% and 60% relative humidity (RH) inside a 20°C controlled environment chamber. Droplet maximal coverage areas increased with droplet diameter but not RH, while droplet fading times increased with both droplet diameter and RH. Although 450 µm droplets had greater maximal coverage areas than 250 µm droplets, the 450 µm droplets had lower ratios of maximal coverage areas to droplet volume and higher fading rates than the 250 µm droplets. Addition of surfactants into the herbicide solutions affected droplet dispersion and fading time on leaves. The UptakeTM surfactant was more effective than the other two surfactants in increasing the droplet maximal coverage area and fading time. Compared to herbicide-only solution, the maximal coverage area was increased by 68% for 250 µm droplets and by 52% for 450 µm droplets with addition of the UptakeTM surfactant but not with addition of the AntiEvap+BS1000 or Enhance® surfactant. Similarly, addition of UptakeTM surfactant into the herbicide-only solution increased droplet fading times by 11.1% at 30% RH and 13.2% at 60% RH for 250 µm droplets, and by 34.7% at 30% RH and 2.8% at 60% RH for 450 µm droplets. Addition of AntiEvap+BS1000 surfactants shortened fading times and addition of the Enhance® surfactant did not significantly affect the fading time. Therefore, appropriate selection of spray adjuvants for herbicide applications can significantly influence droplet deposit behaviors on cucurbitaceae leaves leading to effectiveness of weed controls.