Pasture Management 122A grono my J our n al • Volu me 10 0 , I s sue 1 • 2 0 0 8

Experiments were conducted in the growth chamber and greenhouse to determine the influence of humidity, temperature, simulated rainfall, and oil additives with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide] upon redroot pigweed (Amaranthus retroflexusL.) control. Generally, bentazon gave increased redroot pigweed control with high rather than low humidity. However, the increased weed control with high humidity was greater at 10 C than at 20 or 30 C. A simulated rainfall within 24 hr after bentazon application reduced redroot pigweed control. A simulated rainfall of 650 L/ha within 1.5 hr after bentazon application increased control of redroot pigweed, while more than 1300 L/ha simulated rainfall decreased redroot pigweed control. Emulsifiable linseed oil and petroleum oil additives to the spray reduced the detrimental effect of low humidity and simulated rainfall upon redroot pigweed control with bentazon. Emulsifiable linseed oil was more effective than petroleum oil in reducing the detrimental effect of low humidity and of simulated rainfall. However, emulsifiable linseed oil reduced the redroot pigweed control with bentazon with high humidity at 30 C compared to bentazon applied alone or with petroleum oil.

ALS Gene Mutations in Apera Spica-Venti Confer Broad-Range Resistance to Herbicides Several biotypes of wind bentgrass in Poland have been identified as being resistant to acetolactate synthase (ALS) inhibitors. We screened these weeds with chlorsulfuron and performed a whole-plant bioassay with a range of doses based on these four herbicides: chlorsulfuron, sulfosulfuron, propoxycarbazone-sodium and mesosulfuron-methyl + iodosulfuron-methyl-sodium mixture. Ten biotypes, diverse in their levels of resistance, were submitted for molecular tests. PCR amplification and sequencing of als domains demonstrated numerous single nucleotide polymorphisms. Nine biotypes showed non-synonymous substitutions in codon Pro197, changing it to Ser or Thr. Mutation in Pro197 conferred a high level of resistance to the tested herbicides. Analysis of four biotypes also revealed a substitution in the Ala122 codon, changing it to Val. In one biotype this substitution was not accompanied by Pro197 mutation and this biotype was resistant to chlorsulfuron and mesosulfuron + iodosulfuron, but not to sulfosulfuron or propoxycarbazone-sodium. Correspondence between mutations and levels of resistan ce to ALS inhibitors may support management of resistant weeds with the existing palette of herbicides.

Postemergence difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) for wild oat(Avena fatuaL.) control in spring wheat(Triticum aestivumL.), durum wheat(Triticum durumDesf.), and barley(Hordeum vulgareL.) was evaluated in the field, greenhouse, and controlled environmental chamber. Wild oat control with difenzoquat was greater at the five- that at the three and one-half or two-leaf stages of growth. Barley tolerance to difenzoquat was excellent; however, spring wheat tolerance was influenced by cultivar. Durum wheat generally was more tolerant of difenzoquat than spring wheat. Tank mix combinations of broadleaf herbicides with difenzoquat had no effect on crop injury or wild oat control. Wild oat control with difenzoquat was greatest with adequate soil moisture, adequate fertility, warm air temperatures and high relative humidity. A simulated rainfall of 0.25 mm within ½ h or 1 mm within 4 h of application reduced wild oat control with difenzoquat.

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