An oat (Avena sativa L. ‘Dal’) primary root bioassay procedure was used to study the persistence of eight dinitroaniline herbicides in soil. Sensitivity of the bioassay to the herbicides depended on the length of time roots were exposed to the herbicide treatments. Root inhibition increased with time of exposure. Herbicide persistence was studied under growth chamber, greenhouse, and field conditions. The herbicides remained biologically active the longest under dry and cool soil conditions. At 5 C, little change in herbicide activity was observed over an 8-month period. Under greenhouse conditions, the herbicides in wet soil dissipated rapidly, as compared with those in dry soil. Soil samples taken from depths of 0 to 7.5 cm and from 7.5 to 15 cm in the field showed that the herbicides were retained primarily in the surface 7.5 cm. Small amounts were found from 7.5 to 15 cm only shortly after the herbicides were applied. Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) was the only herbicide tested of which soil residues from spring field applications were not detected the following fall.

The tolerance of several field pea cultivars to glyphosate was compared in the laboratory and greenhouse, using root, foliar, and tissue culture exposure techniques. Pea cultivar response among glyphosate exposure techniques did not always agree. However, the cultivar ‘Alaska’ was consistently one of the most susceptible cultivars regardless of exposure technique. ‘Melrose’ was one of the most tolerant cultivars, especially when its roots and cells were exposed to glyphosate. The response of ‘Frogel’, ‘Glacier’, and other cultivars varied among glyphosate-exposure techniques.