| Summary: | <p>Very little experimental work was done in Saskatchewan before 1971
on the use of herbicides for weed control in irrigated vegetable crops. In
1970 a 2-acre demonstration block at Outlook, Saskatchewan revealed that
onions (<i>Allium cepa</i> L.) would perform well in this area under irrigated
conditions <Young-Zyi 1974). It was also shown that a severe weed problem
existed with this crop. Recommended herbicides were unpredictable,
depending largely upon soil type, moisture level and temperature.</p>
<p>Green foxtail (<i>Setaria virldis</i>(L.) Beauv.) apparently offers very little
competition in well-established cereal crops and therefore causes less
concern to grain growers than vegetable growers. It was initially observed
in field trials by D.H. Dabbs (1983) that green foxtail caused a "drastic
reduction" in onion yields that could not be explained simply by the effects
of competition. Effects were evident even at green foxtail densities as low
as 2.5 plants/m<sup>2</sup>. It did not appear logical that so few green foxtail plants
could be inhibiting onion growth by straight competition for light, nutrients
and water.</p>
<p>Recent reports have stressed the need for additional research on the
biology of specific weed-crop interactions (Chamblee .e.t .al. 1982;
McWhorter and Shaw 1982; Schweizer and Bridge 1982). They point out that
information provided by such research would be useful in establishing
guidelines for specific systems of integrated weed management.</p>
<p>Based on these observations and ideas, it was hypothesized that green
foxtail inhibits onion growth allelopathically. At present, the literature
indicates that approximately 50 weed species throughout the world may
possess allelopathic properties.</p>
<p>Field, growth chamber and laboratory studies were initiated in an
effort to determine the extent to which green foxtail reduces the growth of
onions and secondly) to determine if green foxtail plants possess a chemical
that inhibits developing onion plants. Experiments attempted to separate
competitive effects of green foxtail on onion from noncompetitive
Callelopathic) effects. A third objective was to establish if any cultivar
differences exist in the response of onions to the presence of green foxtail.</p>
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