Earlier this month, Reuters broke the news that the EPA wrapped up its review of glyphosate and plans to release a preliminary risk assessment no later than July, which will include some weed resistance mitigation measures.
And now the USDA has reported that weed resistance — specifically to glyphosate — is more prevalent in soybeans than corn.
The problem of weed resistance, of course, is nothing new.
At the Syngenta-sponsored breakfast held last January at the 2015 National No-Tillage Conference, some 48% of no-tillers surveyed confirmed resistance issues, while 15% said they suspected it.
About 78% of growers said they were concerned or “extremely” concerned about resistant weeds. Nearly half the audience had been no-tilling for 15 years or longer.
In the report “The Economics of Glyphosate Resistance Management in Corn and Soybean Production,” researchers from the USDA’s Economic Research Service (ERS) say that in 2010, growers reported glyphosate-resistant weed infestations on just 5.6% of corn acres, compared to a decline in glyphosate effectiveness reported on almost 44% of soybean acres in 2012.
They also found growers managed glyphosate resistance differently on corn and soybean acres. While the most common action step by growers was to use herbicides other than glyphosate — which is an effective management strategy, the agency says — the next common response was to increase the amount of glyphosate used, which can increase the likelihood of resistance.
Increasing glyphosate use occurred on 39% of soybean acres, compared to 25% of corn acres, the USDA says.
Why is glyphosate resistance a bigger problem on soybean acres?
The ERS’ data estimates show that while corn is treated with a greater quantity of herbicides, more glyphosate has been used on soybean acres than corn.
Part of this is because there are more herbicide options for corn, while glyphosate alternatives for soybeans can be more expensive, less effective and/or cause significant crop injury.
Among No-Till Farmer readers, almost 98% use glyphosate for weed control, our 7th annual Benchmark Study found. The majority of survey respondents — 85.2% — said when they use other chemistries they tankmix them with glyphosate, and 38.9% said they rotate those chemistries with glyphosate sprays. Only 2.3% said they use other chemistries exclusively. Aside from glyphosate, 75% are using atrazine, 75.5% are using 2,4-D and 76.7% are using other residuals or contacts.
To prevent herbicide resistance and keep resistant weeds under control, the United Soybean Board offers a list of management tactics growers can pledge to do this year, such as:
- Knowing your weeds
- Scouting fields regularly
- Planting cover crops to suppress weed growth
- Cleaning equipment to prevent weed seeds from contaminating fields
- Rotating crops
- Applying herbicides at their full, labeled rate
- Using multiple herbicide sites of action
For more information on tackling weed resistance, visit the United Soybean Board’s website.
