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Barley varieties ranked according to competitive ability

Not all cultivars are good competitors.

November 20, 2007  By Bruce Barker

If you want to grow an aggressively competitive barley to help cut down on
herbicide applications, or use integrated weed management (IWM) programs that
depend on competitive barley varieties as one of the cornerstones of growing
a crop that is better able to compete with weeds, then research at the Alberta
Research Council (ARC) gives you some new tools in variety selection. Research
scientist Paul Watson at ARC Vegreville, Alberta, recently compared 29 barley
varieties on their competitive ability.

"Competitive ability is an important integrated weed management tool,
but since competitive ability varies between cultivars and classes of barley,
we wanted to see how varieties compare," explains Watson, who conducted
the research over two years at six locations, in conjunction with Rene Van Acker
of the University of Manitoba and Doug Derksen with Agriculture and Agri-Food
Canada (AAFC) at Brandon.

In the trials, Watson selected two row and six row, malt and feed, and hulled
and hulless varieties. If a variety was grown on five percent of acreage in
its class at the time of the research, in any prairie province, he included
it in the trials. Today, some of the varieties have been replaced by newer releases,
but the results provide a good indication of competitive abilities among classes.
Watson used tame oats as an indicator of weed competition, while broadleaf weeds
were controlled. Oats was selected since wild oats are one of the most competitive
weeds in barley.


Competitive ability was measured as a function of two factors. Ability to withstand
competition was measured as 100 minus percent yield loss compared to the weed-free
check plot. Ability to compete was measured as 100 minus percent dockage.

"We found a wide range of competitive abilities. Yield losses ranged from
six to 79 percent, and dockage ranged from 10 to 83 percent," says Watson.
"Don't assume that just because you are growing barley that it will be
a good competitor. Some are not."

The results showed that the semi-dwarf class was less competitive than the
regular height class. Hulless was less competitive than the hulled class. There
was not a significant difference between malt and feed classes. "Just about
all the poor competitors were semi-dwarf or hulless varieties."

When looking at individual varieties, Watson plotted them on a scatterplot
(see Figure 1) that included ability to compete versus ability to withstand
competition. Varieties in the upper right quadrant were the most competitive,
with reduced weed seed production and higher ability to withstand competition
as evidenced by higher yield.

Looking at the scatterplot, Watson chose 25 percent as an indication of a variety
with good competitive ability, either as a 25 percent yield loss, or 25 percent
increase in dockage. He based that figure on previous work conducted by John
O'Donovan, an AAFC weed scientist who researched the timing of weed removal
and crop competitiveness.

Figure 1. Ratings for 29 barley varieties.
Varieties circled in the upper right indicated very good competitive ability.
The solid lines represent: 1. On the AWC axis, 25 percent yield loss. 2.
On the AC side, 25 percent weed seed yield by weight in the weedy sample.
Malt cultivars are denoted by open circles, semi-dwarf cultivars are underlined
and hulless cultivars are in italics. Source: Paul Watson, ARC.

Watson says that if a grower is looking at the competitive ability of a barley
when selecting varieties, the ability to withstand competition would be more
useful in a conventional production system where weeds can be removed with herbicides.
Ability to compete would be more important for organic growers who do not remove
weeds with herbicides.

"Varieties have a better ability to suppress weeds more than they can
maintain competitive yield. We can't explain why," says Watson. He also
cautions that just because a variety has a better competitive ability, it does
not necessarily mean higher yields. The lack of competitive ability might be
overcome with genetics that provide better yield potential.

Watson also found that a reduction in yield loss (better ability to withstand
competition) does not necessarily mean an equal reduction in weed seed production
– so a variety that has a high ability to withstand competition (resulting
in better yield) could still see many weeds set seed. For example, Harrington
or Manley were able to maintain their yields better, but still allowed increased
seed production as shown by the amount of dockage.

Watson was also hoping that he could provide plant breeders with information
on competitive ability that would aid trait selection in breeding programs.
Unfortunately, ability to compete and ability to withstand competition factors
were not consistent enough to substitute one for the other in breeding programs.

"Competitive ability is somewhat stable, so it would be really useful
for farmers and breeders to know how competitive varieties are when they go
to buy or breed them. All other things being equal, a competitive variety is
better than a non-competitive one," he explains.

What the increasing overall competitive ability does mean, as supported by
research by George Clayton at AAFC Lacombe, is that it could become a component
with other IWM tools such as reduced herbicide rates or increased economic threshold
levels. In addition, farmers who grow varieties in the lower left quadrant will
need to ensure their weed control program is the best possible, in order to
prevent yield losses and weed seedbank increases.

"Growers can use the information as part of their selection criteria in
an IWM system. Competitive ability is another part of the selection package,
along with others like yield potential and disease resistance," says Watson.


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