Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Plant Science


Plant growth regulator (PGR) herbicides are widely used for broadleaf weed control in com, sorghum, small grain, and non-crop areas. Soybean, the most widely grown oilseed/protein crop in the world, is highly sensitive to PGR herbicides and can be exposed by off-target movement from field applications or by contamination of spray equipment. Plant response varies with exposure level and can include leaflet cupping, stunting, stem cracking, and yield reduction. A residue test of foliage from injured plants is frequently requested to determine if PGR residues are present and results may be used in regulatory investigations. Problems arise, however, because the relationship between grain yield reduction and residue amounts at various sampling dates has not been studied. The objectives of this study were to quantify plant response to PGR herbicides (leaf injury, stunting, biomass, and grain yield reduction), determine foliar residue levels over time, and determine if a correlation exists between grain yield ·and residue values at five sampling dates. Experiments were conducted at three locations during 2001 and 2002 to determine the effects of simulated drift rates of two PGR herbicides on soybean. Soybeans were treated at the V3 growth stage with three rates of dicamba (diglycolamine salt) and three rates of 2,4-D (dimethylamine salt). Plants were rated for visual injury and harvested at 0, 6, 12, 24, and 48 days after treatment (DAT) for residue extraction. Soybean extracts were analyzed for herbicide residue using gas chromatography/mass spectrometry with selected ion monitoring for detection and quantification. Visual symptoms caused by PGR treatments were evident by 6 DAT. Symptoms included all of those mentioned above and increased in severity as PGR rate increased. Residue values were correlated with initial application rate, but diminished quickly after application. Dicamba residue values were highly correlated with initial application rate and grain yield reduction at the sampling dates 0, 6, 12, and 24 DAT, but not 48 DAT. 2,4-D residue values were highly correlated with initial application rate and grain yield reduction at the sampling dates 0, 6, and 12 DAT, but not at 24 or 48 DAT. This suggests that plant samples should be collected as soon as possible after PGR exposure for accurate detection and quantification of PGR residue.

Library of Congress Subject Headings

Soybean Plants -- Effect of herbicides on Spraying and dusting residues in agriculture Plant regulators



Number of Pages



South Dakota State University