Genotypes and Environments Alter 2,4-D Herbicide Tolerance in Corn Crop.

Glyphosate herbicide is widely used for weed control in the burndown and crop phases of glyphosate tolerant crops.  Repeated glyphosate applications have selected for resistant weeds and induced weed species shifts.  Growers are now seeking solutions to improve the efficacy of glyphosate on weeds that are more tolerant or resistant to glyphosate.
2,4-D herbicide controls a broad spectrum of broadleaf weeds and is currently labeled for post emergence use in corn.  Due to potential injury to corn, broadcast over-the-top applications of 2,4-D to corn is limited from emergence to 8 inch corn.   Applications after 8 inch corn must be made with drop nozzles. POST applications of 2,4-D from V6-V10 can result in leaning, leaf wrapping, brittle snap and/or malformation of brace roots, and eventually result in yield loss.  It is commonly known that the level of tolerance to 2,4-D  can vary greatly within corn germplasm. Dow AgroSciences has developed a synthetic gene (AAD1) from Sphingobium herbicidovorans, which conveys plant tolerance to 2,4-D and aryloxyphenoxypropionate (“fop”) herbicides by metabolic detoxification.  This gene has been successfully introduced into corn (Zea mays L.).  Field studies have validated that AAD1 provides robust tolerance to 2,4-D across corn genotypes with varying levels of natural tolerance.  Field studies have also demonstrated robust tolerance in AAD1 corn to 2,4-D applied at V4 and V6-V7 growth stages across locations and environments.  It was also found that corn hybrids can show more injury to 2,4-D application than corn inbreds, most likely due to differences in plant vigor and rate of plant growth at certain key stages of development.