Effects of Stimulatory and Inhibitory Levels of 2,4‐D, Iron, and Chelate Supplements on Juvenile Growth of Field Beans 1

S growth regulators stimulate plant growth at low concentrations but inhibit growth at high concentrations. Most reports on the effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on plants deal with inhibitory aspects of herbicidal concentrations (8). Juvenile beans have been used extensively in studies of the herbicidal effects of 2,4-D (1, 3, 4), but few studies deal with stimulatory concentrations on young bean plants. Taylor (5, 6) was among the first to report an increase in soybean plant dry weight from low rates of 2,4-D in nutrient solutions. Weaver (7) applied 2,4-D aqueous solution to the leaves of young red kidney beans and soybeans at rates of 0.001, 0.01, and 0.1 grams actual chemical per square yard. All treatments, measured 31 days after application, reduced plant weight and delayed pod appearance. Swanson (4) reported significant increase in cambial activity in young red kidney beans with the lethal rate of 0.1% aqueous foliar-applied 2,4-D sprays. Leonard (3) reported that aqueous solutions of the triethylamine salt of 2,4-D (150 ppm) slightly increased fresh weight of bean plants 14 days after application to seedling plants. Wort (9, 10) reported that foliar-applied composite dusts or sprays containing a high concentration of 2,4-D and micronutrients increased the early growth and ultimate yield of several crop plants, including beans. The herbicidal and injurious effects of 2,4-D sprays and dusts were decreased or completely eliminated by previous, simultaneous, or subsequent foliar application of salts of iron or copper. This study was designed to extend available data on 2,4-D by determining stimulatory levels as well as herbicidal concentrations. It was of additional interest to determine the effects of foliar-applied iron, chelate iron, and a