SITUATION: Palmer amaranth is the number one problem weed in Georgia. Approximately 84% of the population is ALS-resistant. Add resistance to glyphosate, and the problem becomes more critical.
DISTRIBUTION: The primary areas of resistant Palmer amaranth in Georgia are the Coastal Plain and the Piedmont areas, traditionally areas of high cotton production. Fields in Central Georgia (136 fields) were sampled in 2005 and 2006 to determine the extent of glyphosate-resistant Palmer amaranth; in 2005 and 2006, 49 and 62% of the sampled fields, respectively, had glyphosate-resistant populations. Sampling in 2007 expanded beyond counties in close proximity to the initial field location of glyphosate-resistant Palmer amaranth, and it appears that resistance is spreading. Palmer amaranth has been observed growing in a multitude of ecosystems, including roadsides, forest edges, and in plasti-culture vegetable production systems.
IMPACTS: The occurrence of glyphosate-resistant Palmer amaranth doubles the cost of effective weed control. The herbicides that are the basis for weed control of glyphosate-resistant Palmer amaranth rely on timely rainfall or irrigation for activation to be effective for weed control. In some fields in summer of 2007, growers could not harvest their crop due to their inability to control Palmer amaranth.
RESEARCH: Pollen dispersal: Pollen movement is likely to be a key factor in the spread of glyphosate within and across various Amaranthus species. Information concerning the physical characteristics of the pollen grains, which is needed to predict the potential pollen dispersal distance over the landscape, is as follows: