Multiple regression analysis of data from field experiments conducted in Alberta at two locations between 1972 and 1983 indicated that there was a significant relationship between yield loss of barley (Hordeum vulgareL.) and wheat (Triticum aestivumL.) and relative time of emergence of wild oat (Avena fatuaL. ♯ AVEFA). At a given wild oat density, percent yield loss increased the earlier wild oat emerged relative to the crops and gradually diminished the later it emerged. However, the magnitude of the yield loss for both species varied with the year. Regression equations based on data pooled over years and locations were developed to provide an estimate of yield loss of barley and wheat due to relative time of wild oat emergence and wild oat density. The information should be considered when barley and wheat losses due to wild oat are being assessed.

No abstract

Research Stution, A,qriculture Cunudu, Lucombe, Alberta T)C 150. Contribution ntt.423, reteivetl I0 Apr. l9Bl, uctepred 23 Feb. 1982. O'Sur-r-rvnN, P. A., Kossrrz,V. C., Wtrss

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Moisture and temperature differentially afected the phytotoxicity of four herbicides to tartari buckwheat, Fag$ynnn tatoricznn^(L.) Gaertn., the test plant. The acdvity of the systemiC herbicides 2,4-D, dicamba, and picloram was greatest when conditions of soil moisture and air temperature tended toward optimum growth of the buckrvheat.-When moisture limited growth the phytotoxiciry of these three herbicides was significantly less. Reducing the temperarure from the optimum 2+"-13"C ro l8n-7'C did noc significanrly reduce the activity of thbse herbicides. Conversely, the phytot6xicity of the contact herbicide bromoxynil was siEnificantlv Ereater at the low rather than the high temperature profram. Thii activiry'\;as accentuated when moisture was alio madi limiting buiits efiect was less pronounced. High light intensity tended to result in a6normal buckwheat growth and reduced act-ivity of th-e herbicides.