Researchers at the University of Illinois recently published a paper identifying the PPO resistance mechanism in Palmer amaranth. It turns out that both Palmer and waterhemp have an unusual type of mutation providing resistance to the group 14 herbicides (PPO inhibitors). Rather than a substitution in the nucleotide sequence coding for the PPO enzyme, the two pigweeds have a deletion of three nucleotides. The mutation results in an altered form of PPO, therefore providing resistance to the group 14 herbicides.
The results of the research were featured in an article appearing in Ag Professional. Dr. Tranel discussed the unique opportunity herbicide resistance provides in studying evolution since herbicide resistance evolves over a time frame of 5 to 10 years, compared to hundreds or thousands of years for most evolutionary processes. When asked what farmers can do to deal with the threat posed by herbicide resistance, he responded ‘pray for a new herbicide’.
I assume Dr. Tranel’s response was somewhat tongue in cheek (and shortened for the story), but I still was disheartened by the comment. The evidence is clear that simply relying on new herbicides will not win the arms race with resistant weeds. Herbicides will remain the backbone of weed management for the foreseeable future for most farmers, but we can’t continue to rely on them as the sole tactic used in the fight against weeds. Rather than waiting, or praying, for the next ‘glyphosate’ to be discovered, we need to carefully evaluate our current production system and determine how alternative tactics, whether mechanical, cultural or preventative, can be included in the system in an economical and environmentally sound fashion.