By Bruce Barker
If you didn’t like the winter of 2013-14, just imagine what a winter wheat plant felt like. For winter wheat, having a strong, healthy, disease-free plant established in the fall is critical to over-winter survival, which directly translates into higher yields. To help assess the affect of crop inputs on stand establishment, over-winter survival and yield, research scientist Brian Beres at Agriculture and Agri-Food Canada (AAFC) at Lethbridge, Alta., led a multi-site-year research trial to see if stand establishment and overwinter survival could be improved.
“We were hearing conflicting reports about the effects of seed treatments on crop health and over-winter survival and wanted to find out if there were any impacts,” says Beres. “Growers will continue to grow spring wheat if they have a ‘train wreck’ but when that happens to a new winter wheat grower, he may never try it again. So in order to expand the acreage of winter wheat, we need to develop best practices for stand establishment.”
With funding from AAFC’s Developing Innovative Agri-Products Program, Duck’s Unlimited Canada, Alberta Wheat Commission, Saskatchewan Winter Cereals Development Commission, Winter Cereals Manitoba, and in-kind support from Bayer CropScience, Beres initiated two studies looking at seed and foliar fungicide treatments’ impact on stand establishment.
The first study included 20 sites established over the course of two growing seasons (2010-2011 and 2011-2012) at Lethbridge (irrigated; rainfed clay loam and silty clay sites), Medicine Hat, Beaverlodge and Lacombe, Alta.; Scott, Melfort, Canora, and Indian Head, Sask.; and Brandon, Man. Four seed treatments and a fall foliar application (see Table 1) were compared to untreated checks. The foliar fungicide was applied at the three- to four-leaf stage in mid-October.
Beres says that spring plant stand was not affected by the treatments, even though the stand with seed and/or fall foliar applications looked visibly thicker and greener. He says the fall foliar application produced a spring plant stand that was clean of powdery mildew on the lower leaves, and was more vigorous in colour and appeared to have a better plant stand. Grain yield was improved with Raxil 250 and Raxil WW seed treatments. Foliar application increased yield slightly. Where stripe rust was present in three of the 17 site-years, yield was improved significantly with the fall foliar application.
“But even in those sites without rust, the foliar application seemed to elicit a physiological response that improved the look of the crop and over-winter survival,” says Beres. “While there isn’t a specific pathological explanation for the foliar fungicide response, there is likely a buffer against a stress response in the plant.”
When Beres plotted the results looking at the variability of the treatment against the grain yield, the highest yields with the lowest variability all included a seed treatment plus the fall foliar application. Whether using a foliar application makes sense from an economic perspective was another matter. The highest return was with a Raxil WW seed treatment. Including a fall foliar application along with the Raxil WW reduced the economic return due to the additional fungicide and sprayer application costs.
“For some reason, using a foliar fungicide provided a more stable yield. It didn’t necessarily provide a higher economic yield, but there is something there. When we flesh out the data in more detail for manuscript preparation perhaps we’ll have a better idea,” says Beres. (See Table 2.)
Beres acknowledges that with varieties resistant to stripe rust, stripe rust shouldn’t be an issue since the adult gene resistance means the maturing plant can overcome the stripe rust as the crop grows into maturity. Based on this limited data, growers might want to consider a fall foliar application if stripe rust is present in the fall, or at the very least, consider some test strips.
Taking an integrated approach
In a second trial that paralleled the first, Beres built on the seed treatments by integrating seeding rate and seed vigour at the same 20 site-years. He used two seeding rates of 200 and 400 seeds per metre square (approximately 1 bushel and 2 bushels per acre seeding rate), three seed sizes to approximate seed vigour (light, un-sized and heavy seed), and a Raxil WW (dual fungicide/insecticide) seed treatment. Consequently, he ended up with a range of agronomic systems from weak (low seed rate, small/thin seed, no seed protection) to superior (high seed rate, heavy/plump seed, dual seed treatment).
Winter wheat seed that included a dual (fungicide + insecticide) treatment improved plant stand, winter survival and yield. The positive effect of seed treatment for yield was significant only for the lowest seeding rate. However, a plot of mean grain yield vs. the coefficient of variation indicated that seed treatments generally produced higher, more stable yields. The worst approach was to use poor, untreated seed with a low seeding rate.
“The seed treatment helped overcome some issues like poorer vigour seed and lower seeding rate, but I wouldn’t want growers to look at the results and say I can skimp on seeding rates if I use a seed treatment. When you look at photos of the plots, I think they tell the whole story. Sound agronomic practices along with seed treatments can give you the best stand establishment and over-winter survival,” explains Beres. “With winter wheat, that is what you are aiming for. I think a seed treatment such as Raxil WW is needed for stability and is good insurance, but I wouldn’t recommend it just to compensate for poor agronomic practices.”
Beres goes on to explain that the two trials were implemented using other recommended management practices such as seeding at the appropriate time of the location, seeding into standing stubble with a no-till drill, and taking care of pre- and post-seed weed control. “If you are pushing any of those recommendations, then I think it is even more important to use an integrated approach that includes Raxil WW.”
Summing up, Beres says that using an integrated approach to winter wheat stand establishment has been shown to increase yield and yield stability. Combining a dual fungicide/insecticide treatment along with high seeding rates and vigorous seed can pay off. A fall foliar application has reduced disease loads on plots with and without stripe rust infections in the fall, although the economics of applying a foliar fungicide are tight.
“I think using a dual seed treatment with high seeding rates makes a lot of sense. For the foliar application, I think if stripe rust is present, there may be a case for a foliar application, but there is still lots to answer regarding how much of a benefit it is,” says Beres.