In the years that 2,4–D has been used as a selective herbicide in agricultural areas, an increasing number of reports of its injury to crops has been published. As a result of extensive investigations, lists of susceptible and resistant crops have appeared. Some of the extremely susceptible crops include cotton, sugar beets, alfalfa, tomatoes, peas, beans, cabbage, broccoli, lettuce, grapes, and many others. In response to numerous reports of 2,4–D injury to various small grains, we now consider these plants as being relatively susceptible to 2,4–D at certain stages of development also. The morphological injuries reported may be just as severe as in the case of some of the above-mentioned plants.

Renewed interest in volatility of hormone-like compounds has occurred since government restrictions were placed on the sale of certain esters used for herbicidal purposes. After crop plants neighboring on fields sprayed with volatile herbicides were injured, attempts were made to find low volatile esters which could be used with greater safety. This was done by making long chain esters containing five or more carbon atoms. Since many of these are now being made, the problem is to find satisfactory test methods for determining the relative volatility as compared with known compounds and standard formulations.

Sodium 2,4–dichlorophenoxyethyl sulfate (hereafter designated as SES) has been widely tested for herbicidal use in pre- and post-emergence applications on seeded and vegetatively propagated crops. Several investigators have found this chemical to be particularly valuable for control of annual weeds in strawberries. Their reports indicate satisfactory weed control, but for the most part contain no critical evaluation of the effect of the chemical on the strawberry plants. Field tests conducted on crops other than strawberries have indicated some crop responses which may be characteristic of the general effects to be expected from application of SES to crop plants. More basic studies have shown no hormone response from application of SES to tomato foliage. In fact, the chemical per se was found to be herbicidally inactive, undergoing some change in the soil to attain its active form. The change from inactive to active form was found to occur in nonsterile soils over a range of pH from 3 to 7, and in sterile soils from pH 3 to 4. This change was postulated to be an acid hydrolysis of the ethyl sulfate form of the chemical to an active form, either in an acid soil or as a result of acid secretions of bacteria and fungi. Further research has indicated that SES is hydrolyzed to sodium 2,4–dichlorophenoxy ethanol and sodium bisulfite and that further reaction in the soil may lead to 2,4–dichlorophenoxy-acetic acid. The ethanol has been shown to be highly toxic to germinating seeds, but only 1/100 as toxic as 2,4–D when applied to tomato foliage.

Recently sodium trichloroacetate (TCA) has come to the front as a useful herbicide for the control of annual or perennial grasses. The object of this paper is to report the persistence of the chemical in different types of soils as related to time and rates of applications.

The current widespread use of ester and amine formulations of 2,4–dichlorophenoxyacetic acid (2,4–D) and/or 2,4,5–trichlorophenoxyacetic acid (2,4,5–T) has made apparent the potential vapor hazard of these herbicides in their injury to susceptible crop plants growing nearby. A method used for evaluating the volatility of proprietary formulations was reported previously (1,2) using temperatures of 70° to 75° F. At this “normal” temperature eighty commercial ester preparations representing thirty-one different formulations of 2,4–D and/or 2,4,5–T showed, conclusively, that esters such as the isopropyl, butyl, ethyl, amyl, and pentyl individually or in mixture were volatile; and the iso-octyl, butoxyethanol, tetrahydrofurfuryl, polypropylene glycol, and propylene glycol butyl ether esters were low volatile. These formulations do not comprise all the commercial preparations tested but are given only to indicate the extent of volatility found for 2,4–D and 2,4,5–T ester herbicides commonly available on the market.