Triazine-resistant common lambsquarters (TR-CHEAL) is a widespread weed problem in the northcentral United States. Field studies were conducted from 1995 to 1997 to determine the efficacy and consistency of metolachlor, pendimethalin, and acetochlor applied preemergence (PRE) for control of TR-CHEAL in corn. Pendimethalin provided greater (98%) and more consistent control of TR-CHEAL than metolachlor (66%) or acetochlor (86%). Studies were conducted from 1998 to 2000 to examine the potential of isoxaflutole, flumetsulam, and rimsulfuron plus thifensulfuron for control of TR-CHEAL in corn. In 1999 and 2000, isoxaflutole (35 g ai/ha), flumetsulam (35 g ai/ ha), and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 98% or greater control of TR-CHEAL. In 1998 when rainfall was limited after application, isoxaflutole (70 g ai/ha) and flumetsulam (70 g ai/ha) provided 65 and 55% control, respectively, and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 55% control. Results indicate that control of TR-CHEAL with currently labeled PRE herbicides is possible.

Nicosulfuron and primisulfuron are sulfonylurea herbicides that may persist in the soil and injure sensitive rotational crops such as sugarbeet. Studies were initiated to measure sugarbeet response one and two years after application of 70 and 140 g/ha of nicosulfuron and 40 and 80 g/ha of primisulfuron to corn. Nicosulfuron did not injure sugarbeet one or two years after application. In contrast, sugarbeet yield was reduced one year after application of 40 and 80 g/ha of primisulfuron. Injury was visible two years after application of 80 g/ha primisulfuron but this did not cause a yield reduction. In greenhouse studies, the concentration of nicosulfuron and primisulfuron that reduced sugarbeet growth by 50% were determined for six soils. Primisulfuron reduced sugarbeet growth more than nicosulfuron on four of six soils indicating greater potential for sugarbeet injury from primisulfuron. Sugarbeet response was highly correlated with soil organic matter content (R2= 0.88). The sorption coefficients, Kdvalues, for nicosulfuron were 0.30 to 2.58 and the Kdvalues for primisulfuron were 0.76 to 3.47. Primisulfuron Kdvalues were higher than those of nicosulfuron on four of five soils indicating stronger affinity of primisulfuron for soil sorptive sites. The Kdvalues for both herbicides indicate low overall sorption. The greater sugarbeet injury observed in the field from primisulfuron is not due to greater availability of primisulfuron compared to nicosulfuron.

Mesotrione is a selective herbicide used for preemergence and postemergence weed control in corn. A better understanding of the interactions between mesotrione and soil insecticides is needed to avoid risk of serious corn injury. Field trials were conducted to examine corn injury from mesotrione applied postemergence as affected by insecticide type, application method, and application rate. Corn injury from mesotrione applied postemergence at 0.19 lb ai/acre was 34, 19, and 13% in corn treated with terbufos, chlorpyrifos, and tefluthrin, respectively. In a separate study, corn injury was greater in corn treated with terbufos than clorpyrifos. Injury from mesotrione increased when terbufos was applied at two times the typical rate. Corn injury was higher when terbufos was applied in‐furrow versus T‐band. In each study, corn recovered rapidly from mesotrione injury with no reduction in corn yield. The extent of corn injury observed in these trials indicate that the combination of foliar‐applied mesotrione following soil‐applied terbufos should be avoided.

Field studies were conducted from 2007 to 2009 in East Lansing, MI to evaluate three residual herbicide programs, three POST herbicide application timings, and two POST herbicides in glyphosate- and glufosinate-resistant corn. Herbicide programs included a residual PRE-applied herbicide followed by (fb) POST application (residual fb POST), a residual herbicide tank-mixed with a POST herbicide (residual + POST), and a nonresidual POST. Three POST herbicide application timings included early POST (EP), mid-POST (MP), and late POST (LP) at an average corn growth stage of V3/V4, V4/V5, and V5/V6, respectively. The two POST herbicides evaluated were glyphosate and glufosinate. Control of common lambsquarters and giant foxtail was evaluated 28 d after the LP application. Glyphosate often provided greater weed control than glufosinate. The LP application resulted in greater giant foxtail control compared with the EP application timing, which may be attributed to control of late-emerging weeds. The EP application timing improved common lambsquarters control compared with the LP application timing. The residual + POST program resulted in greater weed control compared with the residual fb POST program in all years. The effect of residual herbicide program, POST herbicide, and POST application timing on corn grain yield varied by year. In 2007, the use of glyphosate resulted in higher grain yield compared with glufosinate. In 2008, corn grain yield was the highest in the PRE fb POST program and with POST applications at EP and MP. To provide the most consistent weed control and minimize the likelihood of grain yield reductions, a PRE fb POST program applied at EP or MP is recommended.

Common windgrass is an increasing winter wheat weed problem in Michigan. Postplant incorporated trifluralin, applied at 0.56 kg/ha, reduced common windgrass density by 85% in small plot research and by 70% or greater in production scale sites. In 1994–1995, incorporation implements had no effect on initial wheat density. However in a spring 1995 evaluation, significant wheat injury and stand reduction occurred in response to trifluralin incorporation. Incorporation implement effects on wheat injury were in the order: flex-tine harrow > spike tooth drag > rotary hoe. When trifluralin was shallowly incorporated over wheat planted at least 5 cm deep, no significant wheat injury was observed at any site. Injury from postplant incorporated trifluralin was related to shallow planting depth.