Acetolactate synthase (ALS)–inhibiting herbicides are often used to control Italian ryegrass in winter wheat in Texas. An Italian ryegrass biotype near Waco, TX was evaluated for resistance to mesosulfuron in field and greenhouse experiments. Control of the biotype in the field was less than 10% with the label rate of mesosulfuron (15 g ai/ha). Greenhouse studies confirmed that the biotype was resistant to mesosulfuron; control of the biotype was less than 35% at 120 g ai/ha mesosulfuron. The herbicide dose required to reduce plant biomass of a susceptible and the Waco biotype by 50% (GR50) was 1.3 and 31 g ai/ha, respectively, indicating a resistance level of 24-fold in the Waco biotype. However, the Waco biotype was controlled with the acetyl-CoA carboxylase inhibitors diclofop and pinoxaden.

Persistent use of herbicides has resulted in the selection of many herbicide-resistant weeds worldwide. A survey of 75 fields in the Palouse region of the inland Pacific Northwest was conducted to determine the extent of Italian ryegrass resistance to grass herbicides commonly used in winter wheat-cropping systems. Plants grown from collected seed samples were tested for resistance to diclofop, clodinafop, quizalofop, tralkoxydim, sethoxydim, clethodim, pinoxaden, triasulfuron, mesosulfuron, flucarbazone, imazamox, and flufenacet/metribuzin. Averaged across herbicide families within a herbicide group, some level of resistance was exhibited in 73, 31, and 31% of the populations to the aryloxyphenoxypropionates, cyclohexanediones, and phenylpyrazoline herbicides, respectively, and 39, 53, and 55% of the populations to the sulfonylureas, sulfonylaminocarbonyltriazolinone, and imidazolinone herbicides, respectively. Twelve percent of the populations showed some level of resistance to flufenacet/metribuzin. Cross-resistance to all acetyl coenzyme A carboxylase-inhibiting (group 1) herbicides was observed in 12% of the populations, whereas 25% of the populations were cross-resistant to all acetolactate synthase-inhibiting (group 2) herbicides tested. Of all the populations tested, 7% exhibited multiple resistance to at least one herbicide within all three groups tested. Only 5% of populations were completely susceptible to all 12 herbicides tested. These results indicate that herbicide-resistant Italian ryegrass populations are now common across much of the Palouse region in northern Idaho and eastern Washington.

Rice by-products were evaluated in the greenhouse for herbicidal activity on various weeds and crops. Rice by-products and corn gluten meal (CG) were applied at 0, 125, 250, 500, and 750 g m−2 preemergence (PRE) and preplant incorporated (PPI). The efficacy of rice by-products and CG in reducing weed emergence and shoot weight of broadleaf species was in the order of medium-grain fatty rice bran (MF) > long-grain fatty rice bran (LF) > CG > defatted rice bran (DF) > long-grain hull (LH) > medium-grain hull (MH). For reducing grass emergence, MF = CG > LF > DF > LH > MH, and for shoot weight reduction, CG > MF > LF > LH > DF = MH. Palmer amaranth and ivyleaf morningglory were the most susceptible weeds (91 and 82%) followed by sicklepod, hemp sesbania, and prickly sida (65 to 70%). Velvetleaf was the most tolerant broadleaf weed. Grasses were not as susceptible to rice bran as broadleaf weeds. In general, MF was the best material for reducing weed emergence and its efficacy was not affected by application method. Cotton and corn were the most tolerant direct-seeded crops to MF (6% reduction in plant stand), and soybean, Italian ryegrass, tomato, and rice had intermediate tolerances (30 to 86% stand reduction). Mustard, cucumber, and lettuce were the most susceptible crops (71 to 98% reduction in plant survival). The minimum effective rate was 250 g m−2 MF PPI or PRE.