The glory days of herbicides might be over. Rather than just finding new types of herbicides, Drs. Davis and Frisvold propose it might be time to find a new approach to controlling weeds.
Since the 1990s, herbicide use per acre has increased. Now the “pesticide use per unit of output has risen more sharply reaching levels double those of the mid-1990s.” So more than double the amount of chemicals (herbicides, insecticides and fungicides) are needed to produce a tonne of a certain crop.
In the mid-1990s, genetically modified, glyphosate-tolerant crops were introduced. The crops (such as Roundup Ready corn) were quickly adopted and became the norm for many crops in conventional agriculture. The result was greater reliance on one herbicide — glyphosate — rather than multiple herbicides. Meanwhile, methods of non-chemical weed control, such as cultivation, have become less common. One result of this is a significant and steady rise in the number of glyphosate-resistant weeds. The agro-chemical industry responded by creating crops that are resistant to multiple herbicides. This enables farmers to spray several types of herbicides on their crops.
Now there are weeds, sometimes dubbed “superweeds,” that are resistant to several types of herbicides. One weed with multiple herbicide resistance is Amaranthus palmeri, also called Palmer pigweed or Palmer amaranth. The resistant weed is spreading quickly through American grain growing areas and can lead to a 75 per cent drop in crop yield in addition to a reduction in crop quality. There are reports of farmers having to sell their farms due to infestations of the herbicide-resistant weed in their wheat fields.
Drs. Davis and Frisvold urge agricultural policy makers, researchers and farmers to develop plans to limit the evolution and spread of weeds with resistance to multiple herbicides and, an even greater challenge, prepare for the potential obsolescence of herbicides. They write, “As Benjamin Franklin famously noted, ‘An ounce of prevention is worth a pound of cure.’ It is up to us to recognize that the time for pesticide stewardship is now. To imbue this societal responsibility with the necessary urgency, we must quantify the catastrophic costs of inaction so that the comparatively modest price of stewardship is fully appreciated for the bargain it is.”
Source: Pest Management Science, Volume 73, Issue 11, pp.2209-2220. 2017.
- Janet Wallace