To implement the production practices mentioned above, McCloskey said these efforts could increase production costs from $20-$40 higher per acre. This amount is lower than cotton production in the Southeast where extra costs can average $50-$60 per acre.

Arizona costs are lower, in part, since growers have more crop options than those in the Southeast. Also — some tillage is already practiced in Western-irrigated agriculture.

How likely could herbicide resistance spread to other Arizona cotton-growing regions? McCloskey said, “Much of it will depend on whether the grower community continues to grow cotton as they have in the past or whether they change their production practices. This is a manageable problem with good management and the use of a wide diversity of tools.”

“This is not a catastrophe for the Arizona cotton industry,” McCloskey said.

Worldwide, glyphosate resistance is found in 24 species of weeds including 13 grasses and 11 broadleaves. In the U.S., there are 15 glyphosate resistant species including eight broadleaves and seven grasses.

The first case of glyphosate resistance in Palmer amaranth was found in a Macon County, Ga., cotton field and reported to the www.weedscience.org website in 2005. Today, most herbicide resistance is widespread throughout the Southeast and Midwest.

McCloskey says resistance can be spread by pigweed pollen and seed. Seed numbers per plant can range from 600,000 seeds to 1.6 million seeds per large plant. An infestation of 1.6 plants per foot of the crop row can produce 600 million seeds per acre.

Seeds can travel at least 1,000 feet.