It's a giant amongst weeds. For that matter, it's a giant amongst men. And wherever it goes, if it gets a head start, it will leave you hoping Superman will show up and wipe it out.
Bill Johnson, Purdue University Extension weed control specialist, is concerned that Palmer amaranth has been identified in a number of counties in Indiana. It's been found in at least one field in about a quarter of the state, but it's scattered from north to south. The highest concentration is in the northwest, but there is a strong pocket in the southwest, and Palmer has been identified in other locations.
Johnson says that if you know you have Palmer or common waterhemp in your fields, treat them as if they are resistant to glyphosate when designing your weed control program. Truth is, not all are resistant in a population, but many are. It's also true that these weeds may also be resistant to other chemistries. ALS resistance in waterhemp is well documented. Make sure you know what class of chemistry you're planning to apply if you suspect you have these weeds.
The problem with Palmer amaranth is seed dynamics. One plant in a crowded stand can produce up to 100,000 seeds. A plant with room can produce up to half a million seeds or more.
Suppose your neighbor has Palmer starting in his field, and he didn't cut out all the plants before they went to seed. Five plants come up in your field. If you don't take them out, that's about 500,000 seeds for next year. If you end up with 500 plants, next time it's 50 million seeds that could be produced! If you've let it go this far, it's a battle you're not likely to win. This is why people talk about how fast Palmer amaranth can take over a field and go from clean to heavily infested in just a few seasons.
Related: How to Identify Palmer Amaranth