Nine cotton Gossypium hirsutum L., cultivars were evaluated to compare the effects of two dinitroanaline herbicides on emergence and seedling characteristics and to determine cultivar differences in response to the herbicides.

After 24 hours in weed germination paper, acid-delinted seed with uniform radicle extension were selected and planted in flats filled with trifluralin (0.56 kg a.i./ha), pendimethalin (0.56 kg a.i./ha) or untreated Freestone fine sandy loam soil. Speed of emergence was determined by daily counts of emerged plants. After 12 days at 20 ± 1°C the flats were flooded and the seedlings were floated out of the soil. Lateral roots were counted and roots, hypocotyls and cotyledons were sectioned and weighed. Seedlings in untreated soil emerged faster and tended to have more lateral roots that seedlings from either herbicide treatment. Pendimethalin was associated with reduced lateral roots but the reduction was not as severe as that associated with trifluralin. Based on number of lateral roots, variation for tolerance to trifluralin and pendimethalin appeared to be related to pendimethalin tolerance. Tolerance to the herbicides was no explained by the differences in seedling weight and height.