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

H. Zhu, J. Lin
Transactions of the ASABE 2016 v.59 no.3 pp. 829-838
Cucumis myriocarpus, droplet size, droplets, esterification, evaporation, glyphosate, leaves, paddies, pesticide application, petroleum, relative humidity, seed oils, spray coverage, surfactants, tissues, triclopyr, watermelons
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 mm(2)to 0.201 ±0.014 mm(2) for 250 µm droplets and from 0.348 ±0.017 nn(2) to 0.537±0.024 mm(2) for 450 µm droplets. Also, their fading times increased from 36 ±7 s to 43 ±6 s at 30% RH and from 53 ±10 s to 62 ±3 s at 60% RH for 250 µm droplets, and from 98 ±6 s to 107 ±5 s at 30% RH and from 145 ±5 s to 151±8 s at 60% RH 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.