Rapid adoption of herbicide-resistant crops, especially those resistant to glyphosate, fundamentally changed weed management strategies. Reliance on residual pre-emergence herbicides and alternative post-emergence herbicides with diverse mechanisms of action was reduced. For example, the number of available herbicide mechanisms of action dropped from six in corn and nine in soybeans in 1995 to only one in 2004 (NASS 2013 cited in Shaner 2014). Pre-emergent herbicides were largely forsaken, particularly in corn, cotton, and soybeans, and multiple applications of glyphosate were used for managing a broad spectrum of weeds (Hurley et al. 2009; Johnson, 2006; Johnson et al., 2007; Prince et al. 2012). The consequence of intense glyphosate use in glyphosate-resistant (GR) crops was a greater selection pressure on weed populations resulting in the evolution of glyphosate resistance in several weed species (Heap, 2024). Currently, there are > 30 glyphosate-resistant weed species in the United States (Heap, 2024). Several of these GR weed populations (especially Palmer amaranth, waterhemp, and horseweed) have evolved resistance to multiple herbicides (Heap, 2024). Resistance to synthetic auxins (2,4-D and dicamba) in GR Palmer amaranth and waterhemp populations has also been confirmed in the US (Figueiredo et al. 2018; Foster et al. 2023; Shayam et al. 2021; Shergill et al. 2018). The multiple herbicide-resistant Palmer amaranth and waterhemp have caused severe yield losses in the two major U.S. crops, corn and soybean, and increased the production costs (Soltani et al. 2016; 2017). For instance, control of glyphosate-resistant Palmer amaranth incurs an additional cost of $40 per ha in corn, $52 per ha in soybean, and $74 per ha in cotton (Carpenter & Gianessi, 2010; Legleiter et al. 2009).

Resistance to glyphosate and/or ALS inhibitors has been confirmed in Palmer amaranth and common waterhemp in the Northeast (NE) and is suspected in common lambsquarters, common ragweed, fall panicum, foxtails (green, yellow, or giant), giant ragweed, horseweed, Kochia, and annual ryegrass populations. Enlist soybean and corn growers in the NE also reported a control failure of waterhemp with 2,4-D, glufosinate, and mesotrione herbicides in summer 2024. Herbicide resistance in weeds in the NE region is increasing and warrants timely evaluation of the suspected weed populations for herbicide resistance evolution, determination of underlying resistance mechanisms, and discovery of alternate PRE and POST herbicides for their timely, economical, and effective control.