The Effects of Row Spacing, Inter-row Cultivation and Herbicide Application
on Weed Control and Alfalfa Seed Production.
H.A. Loeppky1, W. May2 and J.J. Soroka,3
Agriculture and Agri-Food Canada, Saskatoon1,3 and Indian Head,2, SK,S7N 0X2
Seed purity affects marketability and economic return on alfalfa seed,
however, seed stands are relatively non-competitive and weed control options
are few. Integration of agronomic practices and herbicides or cultivation
could improve weed control and reduce herbicide requirements. Field studies
were conducted at 2 sites (Melfort and Tisdale) in NE Saskatchewan to
determine the weed control and alfalfa seed production response to two row
spacings (22.5 or 67.5cm) and several weed control practices including
cultivation or herbicides. Large plots (11m x 73m) of Beaver alfalfa were
direct seeded with a Conserva-Pac® no-till drill into wheat stubble early in
June, 1994, at a seeding rate of 1.25 kg ha-1. In wide-row plots, Roundup®
(880 g.a.i.ha-1) and MCPA Na® (Melfort only, 840 g.a.i.ha-1 ) were applied
between the rows with a shielded sprayer and cultivation was performed
between the rows. Cultivation was also tested in narrow-rowed plots; in this
case cultivation was not confined to between the rows. Pardner® (280
g.a.i.ha-1, in the seedling year) plus Velpar® (960 g.a.i.ha-1, established),
and Pursuit® (50 g.a.i.ha-1) were applied as a blanket application in both
narrow and wide rows. Except for the Pardner/Velpar combination, all
herbicides were applied each year. Permanent quadrats were established so
that alfalfa and weed density could be determined each year, before and after
treatments. Visual ratings of weed control were taken each year approximately
4-6 weeks after treatment. Seed yield was determined in both 1995 and 1996.
Alfalfa establishment was not affected by weed control treatments, however,
plant density was higher in narrow rows than in wide rows, even though the
same seeding rate was used. This could be attributed to less intra-row
competition in narrow rows. Seed yield was not affected by row spacing. In
1995, seed yield was not affected by any of the weed control treatments at
either location. Weed densities were low due to very dry spring conditions.
Roundup, applied between the rows resulted in the lowest yield at Melfort in
1995. In 1996, this treatment significantly reduced seed yield at Tisdale.
It also reduced vegetative growth and delayed flowering at this site, which
may explain the decrease in seed yield. All other treatments did not effect
seed yield at Tisdale and none of the treatments affected seed yield at
Melfort in 1996. Canada thistle, one of the most troublesome weeds in
alfalfa seed fields, was present at both sites when the alfalfa was planted.
None of the treatments significantly changed thistle density at either site,
however, good thistle suppression was observed approximately 21 days after
application of inter-row Roundup (66% control in 1995, 73% control in 1996),
and MCPA Na (79% in both years). Inter-row cultivation provided poor thistle
control in 1995, but in 1996 70% suppression was observed at both sites. By
the end of the growing season, however, the Canada thistle had completely
recovered from these treatments.
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