By Top Crop Manager
Reseeding decisions are dependent on numerous factors.
The 2004 growing season once again served up its share of challenging weather.
A cool spring and moist conditions across the prairies included several rounds
of frost, hail and record rainfall. Researchers in Saskatoon have taken advantage
of these growing conditions to test residual herbicides and their ability to
control weeds in reseeding situations forced by Mother Nature's curve balls.
"What we can tell from two years of trials is that there are choices that
can make reseeding more successful," says Ken Sapsford, research assistant
at the University of Saskatchewan Crop Development Centre.
The trial started with wheat seeded normally and then treated in-crop with
Everest. The crop was then terminated by applying glyphosate to simulate a crop
destroyed by hail, frost, or whatever. Reseeding dates of June 20, 2003 and
June 21, 2004 were chosen as equivalent to the usual last date to qualify for
crop insurance, always an important consideration in reseeding.
In 2003, the plots were seeded in a loam with 4.3 percent organic matter and
pH 7.4, representative of the Dark Brown to Black soils east of Saskatoon. In
2004, trial plots were seeded in a sandy loam soil with two percent organic
matter and pH 7.6, representative of the Brown to Dark Brown soils southwest
"Saskatoon is more or less on the dividing line between soils in Saskatchewan,"
says Sapsford. "By using both sites, results could be applicable to a wider
range of farmland."
Reseeded crops in both years included hard red spring wheat, Clearfield canola,
and flax, while barley was added to the repertoire in 2004. Wide ranges of Everest
rates also were chosen: one-half, normal, and double rates in 2003; one-third,
one-half, two-thirds, normal, one and one-third, and double normal rates in
Mother Nature dealt a wild card in the 2003 trials. After reseeding on the
20th of June, there was no significant rain until the 5th of July. While this
meant slow crop establishment, and ultimately no grain yield of canola or flax
due to the dry conditions, dry soils did also increase the potential for observing
any residual herbicide effects, the whole point of the exercise.
"What we did see was that wheat yield was the same, and canola and flax
establishment in the treated plots was the same as in the untreated plots,"
says Sapsford. "In addition, we did notice residual control of green foxtail
and redroot pigweed. There was excellent control in the one times and two times
plots, and very good suppression in the one-half rate plots."
New year, more tests
The following year of the trial added data on whether Everest could do the same
good job of weed control and what effect, if any, could be seen in the emergency
Yield results will provide further conclusions when the data has been tabulated.
Flax showed some minor thinning and growth effects on a few plots, but yield
measurements will be required to tell if this translated to any economic difference.
Sapsford also noted that the Clearfield canola crop looked very good.
Barley, added as a reseeding crop in 2004, was showing injury at the one-third
rate, as was expected. But the effect was not consistent across all replications,
ranging from 10 to 20 percent up to 70 to 80 percent injury, says Sapsford.
He notes this is consistent with what farmers say they are seeing in their own
What does it mean if growers have to reseed?
on his plant-back research data from the past two years, Sapsford offers these
observations to farmers considering emergency reseeding options in fields treated
with Everest earlier in the spring:
- Clearfield canola and hard red spring wheat are definitely good options
- Flax may be an option in Black and Dark Brown soils.
- Barley is definitely not recommended, due to expected levels of injury.
- In the reseeded crops, Everest showed residual control or suppression of
green foxtail and redroot pigweed so no additional herbicide was needed.
- In the originally seeded wheat plots, Everest treatment resulted in clean
plots. Everest was applied with no broadleaf tank-mix and still showed activity
on broadleaf weeds such as redroot pigweed and wild mustard, in addition to
its main role of wild oats and green foxtail control.
"What is, however, still missing from the picture for farmers faced with
reseeding after a crop is lost in June, is a good short season crop," says
Sapsford. "We have done other trials with winter wheat and fall rye, with
fall rye for example showing no injury even when seeded in August into soils
that have had two times rates of Everest applied earlier in June, and high yield
the next year with no in-crop herbicides. We're hoping further research will
give farmers some sound choices when they are faced with a reseeding challenge."