In the early to mid-1990s, ALS inhibitors, including Pursuit®, dominated the soybean market, offering one-pass weed control of grasses and broadleaf weeds. However, the rapid development of ALS-resistant lambsquarters, ragweed and waterhemp cut into the bottom line due to continuous use of the herbicide.
Costs of ALS-resistant waterhemp
- Initial herbicide application: Pursuit®: $17 to $22 per acre; Application: $5 per acre
- Yield loss from resistant weeds: High densities of waterhemp cut yields by 2.5 percent for each week they compete with soybeans after remaining at least four weeks past the unifoliate stage
- Cost of herbicide rescue treatment such as Cobra® or Flexstar®: Herbicide: $10 to $15 per acre; Application: $5 per acre
Weed shift
Central Corn Belt growers saw very little waterhemp in the 1980s and early 1990s, but many years of reliance on a single chemistry, ALS-inhibitors, allowed waterhemp populations to grow into a major weed problem that is still spreading.
Hidden costs
- More waterhemp in the weed seed bank
- Management time to plan rescue treatments
- Harvest issues due to uncontrolled weeds
Solution for ALS-resistance
Glyphosate seemed to be the perfect solution. Glyphosate-tolerant crop systems decreased soybean production costs to $7 per acre from 1994–1995 to 2004 ; they saved time and labor; supported the no-till and conservation-till systems; and provided simple, flexible and cost-effective weed control.
However, as lambsquarters, ragweed and waterhemp are already resistant to ALS and growing resistanct to glyphosate, very few other chemistries are available to fight resistance.
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