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The introduction and spread of Palmer amaranth in Iowa undoubtedly will have a significant impact on crop production and weed management in the future. However, since the first infestations were identified I've been intrigued by what seemed odd behavior for a plant with Palmer amaranth's reputation.
Most introduced species experience a "lag phase' where they remain at a low level for several years, after this period the plant can spread rapidly throughout the region. The length of the lag phase varies with species, but 20 to 30 years is typical. The lag phase is believed to be due to the need for the plant to adapt to its new environment. Although I have no data to support my observations, I suspect the rate that Palmer amaranth spreads in Iowa at this time is limited...