Effect of 2,4-dichlorophenoxyacetic Acid on Meristematic Tissues of Corn.

In recent years the use of 2,4-dichlorophenoxyacetic acid (2,4-D) as a selective herbicide has become increasingly important in the production of small grains and corn. Yield reductions due to direct injury to the crops are usually small. However, severe yield reductions have occurred occasionally when 2,4-D was used at herbicidal dosages during certain stages of crop growth. Corn plants sprayed with 2,4-D may develop very brittle stems which may be broken off by wind, resulting in a reduction in stand and yield. In small grains the yield reductions are largely due to various abnormalities in the growth of the spike which result in fewer kernels of grain (3). A number of investigators (1, 3, 4, 5, 6, 7, 10, 11) have reported varying abnormalities in plant growth and yield reductions resulting from the application of 2,4-D to spring-seeded wheat, oats and barley at various stages of growth. Yield reductions resulting from applications of 2,4-D are commonly associated with two critical periods in the growth of barley and wheat: (a) an early seedling period when the plants are one to five inches tall and (b) a later period extending from the early boot stage to a few days before heading. A similar though less distinct pattern has been observed in oats. ANDERSEN and HERMANSEN (1) found that the occurrence of spike abnormalities in oats, wheat and barley depended on the stage of development of the various plant parts at the time of treatment with 2,4-D. From this they concluded that the effect of the 2,4-D was on the differentiation of cells forming the first rudiments of a plant organ. DERSCHEID (3) working with oats and barley, showed that stage of growth of the crop plant at the time of application of 2,4-D was the most important single factor affecting subsequent injury as measured by yield of grain. He found that treatments of barley seedlings with 2,4-D reduced yields severely whenever the treatments were made during tiller bud differentiation and during floral initiation. The yield reductions were manifest by a reduction in numbers of tillers and spikes, and by a reduction in seeds per spike. When floral initiation was rapid, the yield reduction was severe only at one or two dates of treatment, but when the floral initiation was slow, the yield reductions were less severe at any one time, but reductions were found in more treatments. Floral initiation in the tillers occurred later than in the central culm of the plants.