Rhizobacteria have the potential to suppress plant growth. We evaluated the effect of native pseudomonads on downy brome (Bromus tectorum L.), a troublesome weed in small‐grain‐producing lands. Pseudomonas spp. were isolated from winter wheat (Triticum aestivum L.) and downy brome roots and tested to determine their potential as biological control agents for this weed. Pseudomonads were screened in agar and soil for inhibition of downy brome root growth and lack of inhibition of winter wheat root growth. Of more than 1000 isolates tested, 81 inhibited downy brome and not winter wheat in the agar seedling bioassay. Six isolates consistently inhibited downy brome growth and not winter wheat in soil contained in pots in the growth chamber. In nursery field trials in which downy brome was planted in rows and adequately fertilized, some of the bacterial isolates reduced downy brome populations up to 30% and shoot dry weight up to 42%. Field studies were also conducted at three sites in eastern Washington in which brome‐inhibitory bacteria were applied to wheat fields infested with natural populations of downy brome. Of the three isolates studied in the field, two reduced plant populations and aboveground growth of downy brome up to 31 and 53%, respectively, compared with noninoculated controls. At two of the three locations, winter wheat yields were increased 18 to 35% because of the suppression of downy brome growth. Brome‐suppressive bacteria isolated from the rhizoplane of winter wheat and downy brome can be used as biological control agents for downy brome.

Imazamox-resistant hybrids resulted from a cross between jointed goatgrass and an imazamox-resistant wheat (cv. FS-4 IR wheat). Two imazamox-resistant hybrids were discovered in a research plot where FS-4 IR wheat seed had been replanted from the harvest of an imazamox efficacy study conducted the year before at a different location. These hybrid plants survived imazamox applied at 0.053 and 0.069 kg ai ha−1in the field and produced seven viable seeds (BC1). This seed germinated, and chromosomes were counted from the roots (2N number ranged from 39 to 54). In the greenhouse, six of the seven plants survived an application of 0.072 kg ai ha−1imazamox, which confirmed that the resistance trait had been passed to these progeny. A large amount of phenotypic variation was observed in the mature BC1plants. A genetic description of the movement of the resistant gene is proposed based on the case of the gene being located on the D and the A or B genomes. Management strategies to reduce the occurrence of herbicide-resistant hybrids are presented.

Adoption of conservation practices by U.S. Pacific Northwest growers to meet farm bill legislation for erosion control is limited by the inability to control weeds and other pests in cereal and pulse crops. A 6-yr, 16-ha integrated pest management field study was conducted in the sub humid wheat area of the Pacific Northwest from 1985 through 1991 to develop a crop production system that controls weeds effectively and reduces soil erosion. Farm-size machinery were used to till, plant, and harvest crops grown in either a continuous wheat (Triticum aestivum L.) sequence or a 3-yr rotation of winter wheat-spring barley (Hordeum vulgare L.)-spring pea (Pisum sativum L.) in conservation and conventional tillage systems. Minimum, moderate, and maximum weed management levels were superimposed over each cropping by tillage system. Position of winter wheat within a cropping system influenced yield so that wheat produced more grain following spring pea > spring wheat >> winter wheat. Insects and root diseases were not yield-limiting factors in either conventionally tilled monoculture wheat or no-till wheat in the 3-yr cropping system. Yield of winter wheat in the conventionally tilled, continuous wheat system was similar for all three weed management levels. Yield of winter wheat in conservation tillage systems increased at both the moderate and maximum level of weed management compared with the minimum level. No-till winter wheat planted after either pea or spring wheat at the moderate and maximum weed management levels yielded a minimum of 605 kg ha-• more than conventionally tilled wheat at the same management levels.

Jointed goatgrass (Aegilops cylindrica) is a serious problem for winter wheat producers throughout the western U.S. Interference from this weed can severely reduce grain yield and contaminate harvested grain, resulting in dockage losses. There are currently no selective herbicides registered for controlling jointed goatgrass in wheat. Imazamox, an imidazolinone herbicide, was applied to an imidazolinone herbicide-resistant (IMI) wheat mutant of the winter wheat cultivar ‘Fidel.’ Jointed goatgrass control from spring postemergence application of imazamox ranged from 61 to 97% when applied at 36 g/ha. Negligible crop injury from imazamox treatment was observed at 36 g/ha at several locations under dryland environments in the U.S. Pacific Northwest. Wheat yield was increased 19 to 41% by imazamox treatment in three of four experiments. Percent dockage resulting from jointed goatgrass spikelet contamination of harvested wheat grain was eliminated by imazamox treatment. Introduction of the IMI trait into commercial wheat cultivars could provide an effective method for selective control of jointed goatgrass in winter wheat.

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