It is reported that the herbicidal activities of Plant Growth Regulators (PGRs) were discovered in the 1940’s.  Then, investigators in England and in the United States started their research on this type of herbicides¹.

Some of these substances are hormones produced naturally by the plants and other are synthetically produced. Examples of naturally occurring growth regulators are gibberellins, auxin, cytokinin. Some stimulate stem elongation and cell elongation. One of the first synthetic selective herbicides developed is 2, 4-D (2,4-dichlorophenoxiacetic acid).
PGRs are used extensively for broadleaf weed control in grass crops in this region such as grain production, bermudagrass, alfalfa, cole crops, sugarbeet, forages, and turf grasses. These herbicides upset the natural balance of the hormones that controls cell division, cell enlargement, protein synthesis, and respiration. That is why this group of herbicides is sometimes called the “hormone herbicides”². In our area growers are very careful using these products due to volatility with our summer temperatures and the problems caused to sensitive crops.

According to a report from Texas A&M “phenoxy growth regulator herbicides are reported to have the least plant activity and soil residual activity; the carboxylic acids generally have the most. Broadleaf crops and turf grasses should not be planted into soils recently treated with these herbicides because they severely inhibit seedling emergence”².
 
Some PGRs: