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The mystery behind yellow wheat unfolds

When looking back at the less than stellar Ontario winter wheat crop of 2009, one of the more visible signs of trouble was the appearance of yellow wheat in the spring. This unwelcome sight was evident in fields from Windsor to Owen Sound. Although the fields shared a common problem, there were many reasons behind the discoloration. “I’m not sure that we came up with any single answer,” says Peter Johnson, Ontario Ministry of Agriculture, Food and Rural Affairs cereal crop specialist. “There was a whole range of things that we looked at and a whole range of things that we found.”

Higher phosphorus prices combined with an increase in no-till cropping may have been the recipe for a significant increase in corn-row syndrome and yellow wheat in 2009.    Photo courtesy of Christine Brown, OMAFRA. Advertisement

The discoveries included viruses such as wheat spindle streak mosaic virus, wheat soil-borne mosaic virus and some barley yellow dwarf virus. Manganese deficiency was another factor. For many fields, Johnson says the yellow wheat was the result of poor weather conditions in both the winter and the spring. “It was everywhere, but to a lesser extent in Essex County, where the weather patterns were closer to normal,” explains Johnson. “Ohio had one of its best wheat crops ever because they had an ideal winter for them, and Essex kind of caught those same conditions.”

Whereas Essex had an average wheat yield of 17 percent above normal, Johnson notes that other counties, including Lambton, Elgin, Middlesex and areas farther north, had below-average yields. The difference, he says, was the weather. “It was a tough winter and spring with lots of frost heave. Then we had a blast of decent weather in April, but it stayed cold and wet in May. And that was just hard on the crop.”

One of the more memorable weather events was a series of thunderstorms that struck some areas with pounding rain from April 22 to April 24. Johnson says that the soils were never the same after being drenched with up to four inches of rain during that period. “For anybody working the ground before that, it was beautiful,” recalls Johnson. “But for the rest of the spring, it never worked up really right until about the end of May. It was likely those rains that really caused soil compaction and made the soil stay cold and wet.”

In his assessment of the yellow wheat problem, Barry Gordon, C&M Seeds sales and marketing manager, says the conditions disrupted the balance of vital factors for growth. Gordon notes that soil requires a good balance of water, air, organic matter and minerals to provide a beneficial environment for crop growth. In the case of the 2009 winter wheat crop, Gordon says certain soils did not get enough air. “I saw that the land was compacted after the winter and didn’t have enough air in it. So therefore, when it didn’t have enough air, all these other things showed up.”

Lower phosphorus applications on the wheat, driven by economic considerations, also had an impact. The appearance of corn-row syndrome underscored the reduced fertilizer use. With the rise in no-till production, corn-row syndrome appears more often as the wheat plants respond to the band of starter phosphorus that is applied with the corn crop, even two years after corn was planted. The condition is characterized by strips of healthy wheat every 30 inches, corresponding with the old corn row, and much poorer wheat in between. “I think some of that corn-row syndrome is a result of the rest of the ground not having good test levels of phosphorus,” says Gordon. “That’s why the band would show up: because the rest of the ground is deficient, whether it’s deficient in the soil or a result of the ground being cold and water-saturated,” says Gordon.

No-till management may be part of the picture
Whatever the case, Johnson is of the opinion that 2009 may have been one of the worst years ever for corn-row syndrome. “It was definitely a horrendous problem last year,” says Johnson. “Part of the reason that it was a worst-case scenario was that we started with incredibly high phosphorus prices in fall 2008.”

Taking note of Johnson’s work on receiving a 7.5 bushel per acre yield boost from applying starter phosphorus in an average year, people calculated their costs and found that the practice would not pay because of the higher fertilizer prices. “It was fair enough that people walked away from using starter fertilizer on wheat because of economics,” Johnson acknowledges. “But it wasn’t an average year; we got probably the toughest winter we’ve had in 20 years and then a tough spring. If we ever needed starter phosphorus it was for this wheat crop.”

As for the potential of the 2010 crop, Johnson says phosphorus prices came down from the previous highs during the summer, allowing growers to buy monoammonium phosphate (MAP) for about one-third of the cost of that in 2009. As a result of the price decrease, he says most growers went back to a seed-placed starter fertilizer.

Gordon, who is also a proponent of using starter fertilizer, was pleased that the economics allowed the farmers to make it part of their management decision in the fall. He says phosphorus assists root development that can lead to a stronger plant for the winter and spring. “If you create a better root system in the fall, you have a better plant going into the winter, better winter survival and a healthier, stronger plant next spring. It’s not like a guarantee against winter kill but it’s certainly a big help,” says Gordon.

Looking ahead to the spring, Gordon says that farmers should also consider an early nitrogen application, especially if the wheat has minimal top growth. He is expecting smaller, shorter wheat to appear this spring because of a lack of top growth last fall. “Late (nitrogen) applications can reduce yield, there’s no doubt about it,” says Gordon. “With more top growth, you can delay nitrogen application in the spring by five to 10 days. For minimal top-growth wheat crops, it’s highly critical to apply nitrogen as early as possible in the spring.”