Quackgrass is a serious weed problem in the northern United States and southern Canada. Field experiments were conducted in 1990 and 1991 to examine the effect of herbicide rate, application timing, quackgrass growth stage, and cultivation on quackgrass control with nicosulfuron and primisulfuron in corn. Nicosulfuron (35 g ai/ha) and primisulfuron (40 g ai/ha) each provided 84% or greater control of two-leaf plants and 93% or greater control of four-leaf quackgrass plants. Sequential applications of both nicosulfuron and primisulfuron provided greater season-long control than single applications of the same rate on two-leaf but not four-leaf quackgrass. Cultivation 10 d after nicosulfuron or primisulfuron application often increased early-season control, but by corn harvest few differences were observed. Postemergence (POST) applications of nicosulfuron and primisulfuron provided at least 88% control, compared with 66 to 86% from an early preplant application of glyphosate. Corn yields were similar regardless of the quackgrass control program.

Growers from three counties in Virginia have recently experienced difficulty controlling shattercane in corn with acetolactate synthase (ALS)–inhibiting herbicides. Seed was collected from these locations and from a susceptible biotype and tested for resistance to imazethapyr, imazapyr, and nicosulfuron in greenhouse trials. Seedlings from these locations were also treated with glufosinate and glyphosate. Greenhouse experiments indicated that one of the four shattercane biotypes was resistant to ALS-inhibiting herbicides. Effective control of the resistant biotype was possible with glufosinate or glyphosate. Field experiments were conducted in 2003 and 2004 to determine the most effective herbicide program utilizing herbicide-tolerant/-resistant corn hybrids for the control of shattercane. Early postemergence (EP) and late postemergence (LP) applications of imazethapyr plus imazapyr or EP nicosulfuron did not control shattercane, and yield from the imidazolinone-tolerant (IT) hybrid was equivalent between these treatments and was equivalent to yield from the weedy control (WC). At 23 wk after planting (WAP), EP applications of glyphosate controlled shattercane 71 and 75% compared to only 21 and 66% with EP applications of glufosinate in 2003 and 2004, respectively. In both years, LP applications of glufosinate or glyphosate controlled shattercane better than did EP applications of glufosinate or glyphosate. Treatment timing with respect to corn yield within either the glufosinate-resistant (LL) or glyphosate-resistant (RR) corn hybrid was critical. EP treatments of glufosinate or glyphosate resulted in yields that were equivalent to yield from the weed-free control (WFC) of each hybrid. LP treatments of glufosinate or glyphosate, however, resulted in yields that were equivalent to only 90 and 91% of yield from the WFC of each hybrid, respectively.

Experiments were conducted in the 2000 to 2001 and 2001 to 2002 growing seasons to evaluate the efficacy of AE F130060 03 plus AE F107892 with nonionic surfactant (NIS) or methylated seed oil (MSO) plus urea ammonium nitrate (UAN) applied in November (early postemergence, EP), January (middle postemergence, MP), and March (late postemergence, LP) for control of Italian ryegrass in barley. AE F130060 03 plus AE F107892 was also combined with MSO and UAN and various postemergence (POST) small grain herbicides at the three application timings. All AE F130060 03 plus AE F107892 treatment combinations controlled Italian ryegrass at least 84% at the three application timings. Treatment combinations of AE F130060 03 plus AE F107892 applied LP generally resulted in lower yields because of increased duration of Italian ryegrass competition, increased barley injury, and insufficient time for barley to recover from the injury. Transient phytotoxicity to barley occurred after EP and MP applications of all AE F130060 03 plus AE F107892 treatment combinations. LP applications of MSO and UAN or other POST small grain herbicides combined with MSO and UAN increased barley injury compared with injury from AE F130060 03 plus AE F107892 applied with NIS. Results indicate that AE F130060 03 plus AE F107892 treatments are an effective method for control of Italian ryegrass in barley; however, treatments should be applied either EP or MP to reduce early Italian ryegrass competition and allow sufficient time for barley recovery from injury before harvest.

Experiments were conducted in 2000 and 2001 to evaluate efficacy of AE F130060 03 plus AE F107892 applied postemergence for the control of Italian ryegrass in barley. AE F130060 03 plus AE F107892 controlled Italian ryegrass when applied at two application rates and at three timings. Barley successfully recovered from initial injury caused by early-postemergence (EP) and middle-postemergence (MP) application timings. The late-postemergence (LP) timing resulted in lower yield than the EP or MP application timings. AE F130060 03 plus AE F107892 applied EP controlled Italian ryegrass similar to flufenacet plus metribuzin applied delayed preemergence (DPRE) when rainfall was received. Barley yields were also similar. However, with insufficient rainfall, AE F130060 03 plus AE F107892 provided superior Italian ryegrass control. EP treatments of AE F130060 03 plus AE F107892 after a DPRE application of flufenacet plus metribuzin or chlorsulfuron plus metsulfuron completely controlled Italian ryegrass and resulted in excellent yields.