Coverage area and fading time of surfactant-amended herbicidal droplets on cucurbitaceous leaves

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

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2016
Publication Date: 7/6/2016
Publication URL: https://handle.nal.usda.gov/10113/5695369
Citation: Zhu, H., Lin, J. 2016. Coverage area and fading time of surfactant-amended herbicidal droplets on cucurbitaceous leaves. Transactions of the ASABE. 59(3): 829-838.

Interpretive Summary: Paddy melon is an exotic weed in semi-arid areas and is a major competitor of crops for water and nutrients. Its infestations are hard to control even with repeated spray applications because consistency and reliability of herbicide performance is often poor under challenging summer dry conditions. Also, long soft hairs on leaves impede spray droplets from breaching the hairy surface and reaching the epidermis. Various practices with combinations of herbicides and surfactants have been recommended to control paddy melons, but it is unclear if these practices are efficient and effective. To answer this question, this research investigated deposition patterns and fading times of herbicidal droplets with different formulations on weed leaves at a microscopic level. Test results demonstrated that droplet coverage areas were increased by over 2.3 times with addition of the seed oil surfactant into the water-only solution but were not affected with addition of the petroleum oil surfactant. Both seed oil surfactant and petroleum oil surfactant enhanced the droplet penetration into plant tissues while the former could have slower evaporation rates for better droplet transport to targets under hot and dry weather conditions. Knowing these behaviors of droplets on weeds will assist to develop better application practices for utilization of systemic herbicides to increase foliar application efficiency.

Technical Abstract: Proper use of appropriate surfactants to control droplet behaviors on leaf surfaces is critical to improve herbicide application efficacy for controlling paddy melons. An esterified seed oil surfactant and a petroleum oil surfactant were investigated to modify spread areas and fading times of water and herbicide droplets on watermelon leaves which were used to simulate paddy melon leaves. A combination of two systemic herbicides (triclopyr and glyphosate) was also used to form a water-based spray solution for comparisons. The formulation of glyphosate herbicide contained a non-ionic surfactant. Tests were conducted with 250 and 450 µm sessile droplets at 30% and 60% relative humidity inside a controlled environmental chamber. The sessile droplets were produced with a single-droplet generator. Droplet fading times significantly increased with both droplet size and relative humidity. Droplet maximal coverage areas increased only with droplet size but not relative humidity. For the water-only solution, addition of seed oil surfactant increased the droplet coverage area by over 2.3 times but addition of the petroleum oil surfactant did not increase the droplet coverage area. For the spray solution containing two herbicides, addition of the seed oil surfactant increased droplet coverage areas on leaves from 0.146±0.012 to 0.201±0.014 mm2 for 250 µm droplets and from 0.348±0.017 to 0.537±0.024 mm2 for 450 µm droplets. Also, their fading times increased from 36±7 to 43±6 s at 30% relative humidity and from 53±10 to 62±3 s at 60% relative humidity for 250 µm droplets, and from 98±6 to 107±5 s at 30% relative humidity and from 145±5 to 151±8 s at 60% relative humidity for 450 µm droplets, respectively. In comparison, addition of the petroleum oil surfactant into the herbicide solution reduced the maximal coverage areas and shortened the droplet fading times but increased droplet penetration rates. Therefore, in order to improve spray coverage area and reduce droplet evaporation, herbicide spray solutions that already contained a surfactant could be amended with the seed oil surfactant. The petroleum oil surfactant could be used when enhancement of droplet penetration into leaf tissues was necessary.