B. Current Uses of Herbicides on Cotton
Glyphosate is generally used as a foliar-applied herbicide. It is most effective for the control of perennial weeds. It is usually applied before planting to kill winter weeds or used as a spot spray at any time throughout the growing season. Glyphosate is also used for destroying weeds growing adjacent to the field.
Herbicides are applied to cotton before planting (to preplant weed foliage or in soil-incorporated applica- tions), at planting (preemergence applications), or after seedlings emerge (postemergence directed or over-the- top). Herbicides were used on 99 percent of the cotton acreage (2.7 million acres) in the Delta region of the United States in 1990, on average from 3.6 to 4.1 treatments per acre. The severe weed pressure in the Delta is demonstrated by the large proportion of the cotton acreage receiving three or more herbicide treat- ments per season. At least one-quarter of the acreage in the Delta is treated with arsenic-based herbicides (DMSA or MSMA), singly or in combination with other herbicides. The total amount of arsenic-based herbicides applied to cotton in 1990 was approximately 3.5 million pounds.
Several postemergence herbicides are registered for use in cotton. They are usually applied when the plants are 3 to 6 inches high. These herbicides include diuron, fluomet- uron, prometryn, and cyanazine, to which MSMA or DMSA is added to broaden the spectrum. One additional application of the mixture is often made during the season since there is a limit of two applications of the arsenical herbicides. Late postemergence herbicides are sometimes applied at or near the time of the last cultivation (“layby”). Direct applications are usually placed between the rows, in order to maintain cotton seed quality. A few over-the-top herbicides are available. The two used are sethoxydim and fluazifop. Both are specific for control of grass weeds and have little effect on broadleaf plants. Before the introduction of sethoxydim and fluazifop, glyphosate was used to control grasses. Because glyphosate is nonselective, special
SAMPLE PETITION—Herbicide-Tolerant Plants