Downy brome (Bromus tectorumL. # BROTE) has developed into a severe weed in several agricultural production systems throughout North America, particularly on rangeland and in winter wheat (Triticum aestivumL.). Several million hectares of winter wheat, pastureland, alfalfa (Medicago sativaL.), grass seed fields, and overgrazed rangeland, as well as other crops, have been invaded by this annual grass since its introduction into this hemisphere. Downy brome is most abundant in the Great Basin and Columbia Basin areas of the western United States, but is found throughout the continental United States and parts of Canada and Mexico. In some cases, the vegetation on overgrazed rangeland consists totally of downy brome, while winter wheat growers in the western United States proclaim it as their worst weed problem. Changes in tillage practices that are currently being implemented for the control of soil erosion coupled with the lack of selective herbicides for the control of downy brome have aided its increase and spread.

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A 2-year study was conducted on a north facing Thatuna silt loam (fine-silty, mixed, mesic Xeric Argialbolls) to evaluate the influence of N fertilizer placement, crop row spacing, and wild oat (Avena fatua L.) herbicides on wild oat populations and wheat (Triticum aestivum L. ) yield in no-till spring wheat. The treatments were factorial arrangements of ammonium nitrate either surface applied preplant or banded 50 mm below the crop seed at planting; wild oat control using triallate (S-(2,3,3-trichloroallyl)diisopropylthiocarbamate) preemergence, difenzoquat (1,2-dimethyl-3,5-diphenyl-lH-pyrazolium) post-emergence, or no herbicide (check); and crop row spacings of either 200, 300, or 400 mm. Surface-applied fertilizer N significantly increased wild oat populations compared with banding the N fertilizer below the seed, but had no effect on dry weight or N uptake. Banded N increased total dry weight N uptake, and grain yields of wheat. These responses indicate that banded fertilizer N was positionally more available to wheat than was broadcast N, but banding N did not reduce availability of N to wild oat. However, surfaceapplied N stimulated wild oat emergence. Triallate decreased wild oat populations compared to difenzoquat or no herbicide, but was no more effective than difenzoquat in reducing wild oat dry weight and total .Kjeldahl N uptake. Both herbicides reduced wild oat dry weight as compared to the no herbicide check and significantly increased wheat yields. Row spacing did not affect wild oat dry weight or total N uptake, but the 200 m row increased wheat dry weight, total Kjeldahl N uptake, and grain yields compared to the 300 and 400 em rows. There were no significant interactions.

Germination of jointed goatgrass (Aegilops cylindrica Host.) seed in nitrate nitrogen (NO−3-N), gibberellic acid (GA3), or distilled water was studied in the laboratory, and depth of emergence of seedlings from soil was studied in the greenhouse and laboratory. After 14 days in germination chambers in distilled water, no difference in percent germination of 1-yr-old or freshly harvested seed existed between 10, 15, or 20 C. Jointed goatgrass seed germinated at temperatures ranging from 10 to 35 C and responded to temperature more than to NO−3-N. Seedlings did not emerge from below 5 cm in greenhouse and 6 cm in laboratory studies even though germination occurred. Jointed goatgrass has the seed germination and seedling emergence characteristics to develop into a severe annual grass weed in winter wheat (Triticum aestivum L.)-producing regions, particularly where reduced-tillage practices are utilized.

Mayweed (Anthemis cotula L. # ANTCO) achenes and seed were germinated in the laboratory at constant temperatures ranging from 5 to 30 C. Maximum percent germination occurred at 20 C for both achenes and seed. Under all conditions tested, achene germination was less than seed germination. Both acid scarification for 15 min and soaking in 14 mM gibberellic acid (GA3) more than doubled achene germination. Pericarp leachate inhibited achene and seed germination only at high concentrations, indicating that inhibitors in the pericarp are not a primary cause of low germination in achenes. Optimum germination of achenes and seed occurred at pH 4.5 and over a range from pH 3 to pH 6. Achene germination was inhibited to a greater degree by moisture stress than was seed germination. It appears that structural integrity of the pericarp is the predominant factor affecting mayweed germination.