Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

First Advisor

C. Dean Dybing


To learn more about oils and how they affect post-emergence spray applications of herbicides, two major problem areas were investigated. The first dealt with specific physical and chemical properties of oils as they are associated with phytotoxicity and enhancement of herbicidal activity, while the second dealt with foliar penetration as a possible mechanism of enhancement. Simple correlation and multiple regression analyses were conducted for specific properties of mineral oils applied to green foxtail (Setaria verdis (L.) Beauv.) and grain sorghum (Sorghwn bicolor (L.) Moench. 'Northrup King 133') as 5% oil in water emulsions with and without 2.24 kg/ha of atrazine (2-chloro-4-(ethylamino)-6- (isopropylamino)-s-triazine). Simple correlations identified individual oil properties important in explaining dry weight variabilities, but these single properties generally accounted for only a small portion of the total dry weight variability. Analyzing several oil properties by multiple regression analyses accounted for 99% of the variability due both to phytotoxicity and herbicide enhancement. Each of several combinations of eight different oil properties accounted for most of the dry weight variability because the properties were not mutually exclusive. Those properties most highly associated with atrazine enhancement included distillation temperatures, pour point, viscosity, viscosity index, refractive index, and flash point. Phytotoxicity of oil alone was associated with increased aromatic contents and decreased unsulfonated residue values. These findings were slightly altered when natural (crop) oils were included with the mineral oils due to inherent differences in the properties of the two types of oils. Several oils used as 5% oil/water emulsions significantly increased the herbicidal activity of atrazine on foxtail and sorghum when compared to atrazine in water alone or with 0.1% surfactant. Penetration of 14C from atrazine and dicamba (3,6-dichloro-o-anisic acid) through astomatous leaf surfaces of Tradescantia (Tradescantia fluminesis Vell.) was increased by use of oil-water emulsion as compared to 0.1% surfactant solution. Most of the radioactivity was found below the treated leaves of Tradescantia plants 1 day after treatment but accumulation in the plant parts above treated leaves increased by the 6th day. 14C-labeled mineral oil likewise was found to penetrate and translocate in the Tradescantia plants. Uptake of 14C from the oil increased from 20 to 57% in the first 6 days after treatment. Little additional uptake was noted at 15 days. Measurements of CO2 uptake by sorghum revealed that photosynthesis was completely inhibited 1.5 hours after treatment with atrazine in oil-water emulsion. Maximum penetration of 14C-labeled herbicides through isolated astomatous cuticles of Prunus armeniaca L. (apricot) leaves occurred (a) at warm rather than cold temperatures, (b) when chloroform extraction was used to remove wax prior to treatment, (c) from the air side of the cuticle to the mesophyll side rather than in the reverse direction, and (d) when oil emulsions were used as the carrier in short treatment periods compared with 0.1% surfactant. Penetration of 14C from dicamba was more rapid than absorption of 14C from atrazine. Autoradiographic studies using isolated astomatous apricot cuticles showed that cuticle areas over veins were preferred sites of entry for 14C from oils in both pure and emulsified forms and for 14C from dicamba regardless of carrier type. No preferred sites of penetration were found in cuticle areas directly above an individual cell whether the underlying cell was in a vein or non-vein area of the leaf.

Library of Congress Subject Headings

Weeds -- Control



Number of Pages



South Dakota State University