Glyphosate-resistant kochia confirmed in Neb.
Why Does Herbicide Resistance Evolve?
Herbicide resistance usually results from repeated use of the same herbicide. An over-reliance on glyphosate facilitated by widespread adoption of glyphosate-tolerant crops in the Midwest (primarily corn and soybean) has resulted in the evolution of glyphosate-resistant weed populations. The selection pressure exerted on weed populations by increased glyphosate use over the last 10 to 15 years is unprecedented in the era of herbicide weed control.
Only a few weed species worldwide were resistant to glyphosate prior to the introduction of glyphosate-tolerant crops. Currently, 12 weed species in the U.S. have evolved glyphosate-resistance due to repeated glyphosate use over a large land area (more than 300 million acres just in the U.S.). They are common waterhemp, giant ragweed, common ragweed, kochia, palmer amaranth, marestail (horseweed), hairy fleabane, junglerice, goosegrass, Johnsongrass, Italian ryegrass, and annual bluegrass (source: http://www.weedscience.org/).
Over-reliance on a single weed management tool will likely cause inconsistent and eventually ineffective control. While weed management is not impossible in the presence of resistant species such as glyphosate-resistant kochia, it is certainly more difficult. As new herbicides and traits reach the market, it is important to note they are in known herbicide mode-of-action classes. It has been more than 20 years since a new herbicide mode-of-action was introduced for row crops. Thus, it is imperative that we are good stewards of the current herbicides to delay the evolution of resistance as long as possible.