Organic matter is the soil constituent most often associated with herbicide adsorption. Structural diversity makes humified organic material an ideal substrate for the adsorption of many pesticides, but variability in composition and distribution in situ complicates interpretation of its quantitative effect on adsorption. Variability in the adsorption distribution coefficient (KD) of a herbicide among soils often is due to differences in organic matter content and can be reduced by adjusting KD for soil organic carbon content and computing the organic carbon partition coefficient (Koc). Koc can be estimated from the octanol-water partition coefficient (Kow) of organic compounds, but the correlation weakens as compound polarity increases. Koc also can be correlated with aqueous solubility if a correction is made for the melting point of compounds that are solids at 25 C. Relative adsorption can be estimated from parachor and molecular connectivity indices; but corrections are needed for polar compounds, and correlations with KD or Koc have been variable. Such predictive methods may be useful for broad classification purposes, but accurate extrapolation generally requires site-specific adsorption measurements. Empirical models which accommodate the multiple regression of organic matter content and other soil properties such as clay content, pH, and cation exchange capacity on herbicide adsorption can increase accuracy, but interpretation may be restricted to a small number of sites.

Dinitroaniline herbicides are absorbed readily by roots and emerging shoots, but shoot exposure is more phytotoxic. Translocation within the plant varies by specific herbicide but commonly is minor. Dinitroaniline herbicides injure plants by binding to tubulin, a dimer protein in the ceil that polymerizes to form microtubules (MTs). MTs form the major part of the mitotic apparatus, including spindle fibers, which enable chromosomes to separate during cell division. Dinitroaniline herbicides prevent tubulin from polymerizing into MTs, thus arresting mitosis. This leads to abnormal cells with more than the normal complement of chromosomes and, frequently, lobed nuclei. MTs also are responsible for orienting cell wall microfibrils in such a way that they prevent lateral enlargement of cells. Treatment with dinitroaniline herbicides leads to disorientation of the microfibrils, leading to one of the common symptoms—spherical cells instead of rectangular ones. Studies on the metabolism of trifluralin in plants have shown that amination, dealkylation, and cyclization all can occur. However, metabolites often amount to a small percentage of the original herbicide. In general, trifluralin seems quite stable within the plant.

Jimsonweed, Jamestown weed, datura, stramonium, thornapple, tolguacha. These are some of the more than a score of common English names used for jimsonweed (Datura stramonium L. #3 DATST), a cosmopolitan weed of worldwide distribution. The above names are those used most widely in the United States. Jimsonweed is a corruption of Jamestown weed, the name given the plant in colonial days because it first grew in and around Jamestown, VA (2). It had been brought from England as a medicinal plant. Boiled with hog's grease, jimsonweed made a healing salve for burns from “fire, water, boiling lead, gunpowder, and lightning” (2).