Pennsylvania smartweed is native and present through much of the continental US, and a triazine-resistant population was confirmed in Iowa in 1990, infesting corn. So far, the only reported triazine-resistant cases remain in Iowa. It is a somewhat competitive, low-growing invasive plant that spreads rapidly by rhizomes in row crops. This weed should be managed when seedlings are small, as they get more difficult to manage as they mature and spread.
Integrated weed management recommendations include: rotating to small grains and forages, tilling at night in May after smartweed emergence, cleaning tillage equipment to remove entwined rhizomes. For chemical control of triazine-resistant populations, use tank mixes that include effective modes of action other than atrazine.
Herbicide resistant populations:
- Group 5
Locations of resistant populations: