COC's are frequently classified by the type of oil used to manufacture them, either a petroleum-based oil or a modified vegetable oil. The attachment of the methanol to the oil alters the HLB of the oil to an optimum level. Methylated seed oils seem to have the greatest advantage over traditional COC's in situations where weeds are under stress from environmental conditions. The final class of additive used are the nitrogen based fertilizers. It is believed that the ammonium ion is largely responsible for the beneficial effect of fertilizers on herbicide performance.
Adjuvants can enhance herbicide activity in several different ways.
The effect of surfactants on the surface tension of spray droplets is well documented. The epicuticular wax on the surface of leaves repels water, resulting in beading of spray droplets as they land on leaves. In some situations a high percentage of spray droplets may simply bounce off leaves, resulting in the herbicide falling harmlessly to the ground. An increase in spray coverage is especially important with contact herbicides that do not move within plants. In most situations the optimum effect of surfactants is reached at concentrations higher than needed to minimize droplet surface tension.