Abstract
Methylated seed oil (MSO) is a recommended adjuvant for the newly registered herbicide topramezone in China and also in other countries of the world, but the mechanism of MSO enhancing topramezone efficacy is still not clear. Greenhouse and laboratory experiments were conducted to determine the effects of MSO on efficacy, solution property, droplet spread and evaporation, active ingredient deposition, foliar absorption and translocation of topramezone applied to giant foxtail (Setaria faberi Herrm.) and velvetleaf (Abutilon theophrasti Medic.). Experimental results showed that 0.3% MSO enhanced the efficacy of topramezone by 1.5-fold on giant foxtail and by 1.0-fold on velvetleaf. When this herbicide was mixed with MSO, its solution surface tension and leaf contact angle decreased significantly, its spread areas on weed leaf surfaces increased significantly, its wetting time was shortened on giant foxtail but not changed on velvetleaf, and less of its active ingredient crystal was observed on the treated weed leaf surfaces. MSO increased the absorption of topramezone by 68.9% for giant foxtail and by 45.9% for velvetleaf 24 hours after treatment. It also apparently promoted the translocation of this herbicide in these two weeds.
Highlights
Almost all herbicide formulations contain adjuvants which act as important tools to improve physical aspects of herbicide application and/or to enhance biological efficacy [1,2,3,4]
Methylated seed oil (MSO) is a kind of fatty acid from seed oil esterified with methyl alcohol [5]
The ED90 value of treatment topramezone with MSO was only 33.53 g a.i. ha21, while the ED90 value of treatment topramezone alone was 85.06 g a.i. ha21
Summary
Almost all herbicide formulations contain adjuvants which act as important tools to improve physical aspects of herbicide application and/or to enhance biological efficacy [1,2,3,4]. For oil-based adjuvant, droplet spread on leaf surfaces and herbicide penetration seem to be the two predominant factors regarding the mechanism of the enhancement in herbicide efficacy [6]. Xu et al reported that MSO could decrease the surface tension and contact angle and increase the wetted areas of droplets on both waxy and hairy leaves [7,8]. Some reports have shown that MSO enhances the efficacy of several herbicides on certain weed species by increasing the absorption of the herbicides by weeds [9,10,11,12,13,14,15,16]. When applied as a post-emergence herbicide, it controls a wide spectrum of annual grass and broadleaf weeds [18,19,20,21] and is safe to corn (Zea mays L.) [22,23]
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