EDMONTON – Farmers across the Prairies are in danger of serious crop damage this year from herbicide residue left in the soil from last year’s dry weather, says a weed specialist.
“It’s very serious,” said Denise Maurice, manager of agronomy products with Westco.
“That’s why I’m telling people now they must plan ahead,” she told farmers at the FarmTech 2003 conference.
Farmers in the black soil zone who have never worried about herbicide residue are in the most danger, she said.
“Typically in the black soil zone we’ve had complete breakdown. Those are the people we want to get at. They haven’t worried about herbicide resistance in the past. They’ve had the luxury of breakdown.”
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Herbicides take from a few days to several months to break down in the soil, but unless the label mentions long-term persistence, farmers have generally been able to seed crops the following spring with little worry about residue in the soil.
Not this year, Maurice said.
Soil moisture is one of the keys to herbicide breakdown and it’s in short supply across much of the Prairies.
“Soil water is the absolute criteria in the breakdown of the product,” she said.
If the soil is dry, farmers should be wary of what crops are planted in the spring because plants not normally sensitive to herbicide may be in danger.
“With the new hybrid canolas, we’re paying good money for that seed,” said Maurice, who worried many crops will be damaged by herbicide residue.
Organic matter and soil pH, texture and temperature also affect herbicide residue. Many Group 2 herbicides, such as Refine Extra, Ally, Express and Muster break down more quickly in acidic soil and persist longer in alkaline soils
Clifford Cyre of Barrhead, Alta., said his field became a giant test plot for chemical resistance last year. High pH levels had slowed herbicide breakdown in 2001 and he had a lot of crop damage in 2002.
“The pH wasn’t mentioned in the Blue Book,” said Cyre, referring to the guide of chemical labels.
Maurice said knowing the field’s pH is becoming more important.
Organic matter can also absorb large amounts of herbicide, which means it will persist longer in fields with high levels of organic matter.
Herbicides will also break down faster when soil is warmer than
15 C. Early freeze up in the fall and late spring thaw do not allow sufficient time for herbicide breakdown.
Maurice recommended that farmers get an analysis of organic matter and pH when they do their soil tests.
If they are concerned about a certain field, Maurice recommended a field bioassay, in which soil samples are sent to a lab to determine if and how much residue is in the soil. However, she warned it can take five weeks for the results.
How to avoid or minimize herbicide carry-over
- Integrated weed management: Use a variety of seeding dates, crop selection and fertilizer placement to promote a vigorous competitive crop that has an advantage over weeds and helps to minimize carry-over.
- Herbicide rotation with crop rotation: This is important to reduce the need to apply herbicides that may carry-over in the soil in successive years.
- Selection of herbicides with minimum carry-over potential:
Choose herbicides with little or no carry over given local soil
and weather conditions.
- Apply minimum rates of herbicides: The rate of herbicide should never be more than the amount required to achieve acceptable weed control.
- Time of application: Early removal of weeds reduces competition and improves crop yield. The longer the herbicide is exposed to moisture and temperature, the lower the risk of carry-over.
- Accurate application: Always read the label and follow instructions. Avoid sprayer overlap.
- Grow a tolerant crop: When herbicide residue is detected or suspected, a tolerant crop should be grown.
- Soil additives: Absorption of herbicide residue can be increased by the addition of absorbent material such as activated charcoal.
- Application of fertilizer: The addition of fertilizer enhances the growth of tolerant plants, which increases the uptake of herbicide
from the soil.
Source: Westco
