Jake Jones, Extension Agriculture Agent, Kent County; jgjones@udel.edu
At this point in the growing season, the success of your herbicide program becomes apparent. Timing is vital to controlling Palmer amaranth and killing plants above the canopy with herbicides is nearly impossible. The key is to spray Palmer amaranth when the plants are under 3 inches tall. So what should you do when the plants are 5, 6, 7 feet tall? If the infestation isn’t too severe, hand rogueing is the best option to reduce next year’s seed bank. After a rain/irrigation you should pull the Palmer amaranth plants up by the roots and remove them from the field. If they are laid back in the field they can re-root and continue growing. Once they are out of the field, composting the plants is one option and will kill the seeds as a result of temperatures between 131-170°F. Burning is another option, but the ban on open burning during ozone season (May 1-September 30) prevents this disposal method, unless it is an emergency, until October 1. Once the first round of Palmer amaranth plants are rogued, you should continue to monitor those fields for smaller plants that emerge from the soybean canopy later and repeat the process.
Fields that you know have Palmer amaranth, and infested areas within those fields, should be harvested last to limit the spread of this noxious weed. Equipment sanitation is important to limit Palmer amaranth spread from field-to-field. Used compressed air to clean combines from the top down and then run 2-3 bales of straw through the combine (clean-out video: https://integratedweedmanagement.org/ index.php/2019/03/20/the-straw-bale-methodology-for-cleaning-weed-seeds-out-of-a-combine/). Considerations for infested fields next year include: crop rotation, in order to utilize different herbicides and the use of residual herbicides in your spray program.
Hand rogueing is not fast or easy work but is an investment that will pay off in the years to come.
A golden opportunity to prevent future expense and aggravation.