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Weed control after a flood

Many farmers saw flooded acres in 2011. Special care will be needed to control weeds and manage these fields this year

It may only occur every 300 years, but farmers in southeast Saskatchewan and southwest Manitoba spent 2011 dealing with the worst flood since the West was settled. An estimated six million acres in the two provinces went unseeded due to the flooding. Even though waterlogged fields could not be planted, they were anything but barren, and now pose several management issues for the spring of 2012.

“We had a lot of weeds,” says Greg Gerry an agrologist, owner of Precision Agricultural Services, and a farmer near Griffin, Saskatchewan, an area severely affected by the flood. He goes on to say, “We buried a lot of weeds, we are going to have a lot of weeds to kill, but we don’t have new weeds.”

Weed control tools

Although it is possible that flood waters could have washed in weed seeds currently not found in the affected fields, Gerry sees this as an unlikely possibility. The greater problem by far is the bank of weed seeds that has been created when weeds have been allowed to grow and mature unchecked due to the wet conditions.

The quantity of weed seeds is concerning. The greater the quantity, the more flushes of weeds that will be able to grow come spring. Field work last fall, such as cultivating, and putting weeds through the combine to reduce the straw residual, may have contributed to the problem. “The seed bank is buried, so the problem is going to be ongoing. There are a lot of tools to control the weeds. With a warm spring there will be a lot of flushes. Burn-off will be essential,” says Gerry.

The “tools” to control weeds referred to by Gerry, are, of course, farm chemicals, such as glyphosate. Gerry recommends farmers look at using glyphosate with an add-on such as Express Pre-Pass, or glyphosate and Heat for spring burn off. For in-crop control of weeds, such as wild oats, Gerry recommends spraying with Everest.

He’s cautioning farmers to be aware of what weeds they have in their fields, so they can use the right product to eliminate their specific weed problem. Gerry says, “Perhaps because we had so many weeds, it created more awareness of what is out there. We are seeing harder to kill weeds such as cleavers and catchfly.”

Other post-flood problems

Being aware of the potential weed problems caused by the flood of 2011 is going to be an important part of field management for the spring of 2012, however, Gerry cautions farmers in the affected regions to also be aware of several other potential problems they may be facing this spring.

One of those potential problems is crusting. Crusting occurs when the structure of waterlogged soil breaks down and forms a compact layer on the surface. Crusting not only impairs the movement of air and water in the soil, but can also impair the emergence of seedlings. Seeding into crusted soil may be an issue, although this can usually be solved by harrowing prior to seeding.

Another potential concern for seeding this spring is residual products in the soil. Farmers must remember what they sprayed on their fields last summer and fall to control weeds. If a crop that is sensitive to a certain residual is planted on a field with that residual, the results may be disastrous. For example, if metsulfurson, a residual broad leaf herbicide, was applied in the summer of 2011, lentils could not be planted on this field, as it would destroy the crop’s root system.

Deficiencies in nitrogen and sulphur can occur in waterlogged soil. “Don’t assume you will have nitrogen because the field stayed fallow last year,” Gerry warns. He says that under wet conditions nitrogen becomes mobile, and will find its way to the surface where it will gas off into the atmosphere. Also, certain microorganisms have the ability to obtain oxygen from nitrites and nitrates in waterlogged soils, therefore further reducing the quantity of nitrogen. Sulphur may suffer a similar fate in wet soils, as excess moisture allows the sulphur to leach from the soil.

Gerry recommends that farmers soil test last year’s flooded fields to learn the amount of fertilizer in the soil, and determine what requirements each field has for the pending growing season.

Farmers in the flooded areas may encounter some insect problems they would likely not typically encounter. One example is the flea beetle. Flea beetles are heat sensitive. An increase in the number of black summer fallow acres means an increase in temperature in those fields, which could translate into an increase in flea beetle numbers. “We may see higher flea beetle numbers then we’ve seen in years,” says Gerry, “Guys aren’t ready for that because we aren’t used to summer fallow.”

Whether the issue is weed control, crusting, residuals, nutrient deficiencies, or insect pests, farmers in Southeast Saskatchewan and Southwest Manitoba will still be feeling the effects of the 300-year 2011 flood as they prepare for the 2012 growing season. †

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