Dry Summer Reduced Some — But Not All — Crop Disease

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Last summer s dry weather stopped a lot of crop diseases, but not all of them. The cold, late spring with many saturated soils was followed by dry weather in most of the province (save in the Peace where the end of a long drought was followed by almost constant rains). The dry weather meant fusarium head blight was just about a non-issue in Alberta and much of the Prairies this year.

Only 5.4 per cent of durum and 3.5 per cent of hard red spring wheat samples his group has assessed have fusarium damage this year, said Tom Graefenhan of the Canadian Grain Commission.

But it s a different story for ergot, with 19.5 per cent of hard red spring wheat samples testing positive.

Ergot is sporadic, said Graefenhan. But it s serious for farmers because tolerance for ergot is very low, 0.01 per cent for No. 1 and only 0.04 in No. 4 HRS. We ve had bad years for ergot before, 12.7 per cent in 99 and 13.5 per cent in 08. But it doesn t usually persist into the following year.

Tolerance for ergot has to be strict because it contains alkaloids that cause nasty problems, including gastrointestinal effects, hallucinations and gangrene that can result in the loss of fingers and toes.

A wet year, such as Alberta had in 2010 favours ergot in grain or in grasses in ditches and headlands, and they produce abundant inoculum. The following year, the ergot bodies on the wet soil surface germinate and two to four weeks later produce infective spores. Open-pollinated species, such as rye, triticale and ryegrasses, are relatively easily infected because their flowers open to accept pollen. Usually, flowers of self-pollinators, such as wheat and barley, are not open to pollen from other flowers or infective spores.

The problem, says Agriculture Canada plant pathologist Kelly Turkington, is that an environmental stress just before or during flowering can cause male sterility in self-pollinating species, with the anthers producing no pollen or nonviable pollen. This leads to flowers opening in order to access pollen, and that can result in ergot infection, in which spores infect the flower and replace the seed with an ergot body.

Environmental triggers

The environmental stress that triggers male sterility may be a cold snap or a hotter-than-normal spell, a late herbicide application, or a deficiency of copper or boron in the soil.

Copper deficiency or boron deficiency can trigger male sterility, especially on sandy soils, says Turkington. But applying copper or boron doesn t always prevent wheat and barley developing male sterility. If these nutrients are at deficient levels then there is a greater ergot risk, but only if ergot spores and wet conditions occur during the flowering stage of the crop.

Researchers in Britain have tested a wide range of fungicide strategies, but none were very effective.

Rotations are key to ergot control, says Turkington. Really, you need two years between cereal crops to lower disease risk. Mowing grasses in ditches and headlands before they head out can lower your risk of ergot in the crop.

Once you have ergot in the crop, Turkington suggests leaving the ripe grain standing so the wind can shake the loose ergot bodies out of the grain heads. Given the low tolerances for ergot in grain it may be worthwhile to have grain cleaned before shipping.




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