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Should you invest in treating weeds in winter wheat?

K. George Beck and James Sebastian, CSU, cheatgrass (downy brome) nearing seed set growth stage
ALWAYS SPRAY: Any winter wheat field with a downy brome problem needs to be treated. It, along with cheatgrass, can cause up to 60% yield loss. Here is a downy brome nearing the seed-set growth stage.
Know the amount of yield loss caused by these four annual weeds before spending money on herbicides.

Weeds may be popping up in your winter wheat stands, but is treatment worth the price tag?

Killing common annual weeds in winter wheat may or may not be a good financial decision, especially when input costs are high, says Kevin Bradley, University of Missouri Extension weed scientist.

Winter wheat is one of the most competitive crops planted, Bradley says.

He offers these crop production management guidelines for four annual weeds farmers see in winter wheat, based on research from MU and other sources.

1. Common chickweed. Yields drop when weed densities are at least 30 plants per square meter and higher. MU research found that wheat yields dropped 28% with common chickweed densities of 169 plants per square meter.

2. Cheatgrass/downy brome. “Herbicide applications are almost always warranted in fields with cheat and downy brome infestations,” Bradley says. “This is especially true when these grasses emerge at or within the first few weeks after wheat planting.”

In 1997, Oklahoma researchers observed a 49% reduction in yields when cheat infestations were 86 plants per square meter. In 1993, another report saw wheat yield reductions greater than 60% in fields with 200 downy brome plants per square meter.

3. Italian ryegrass. Herbicide application is usually warranted for Italian ryegrass, a very competitive weed. Ryegrass tends to develop resistance to herbicides and robs wheat of nutrients such as nitrogen and potassium. Many studies show that Italian ryegrass in wheat lowers yields.

A 1997 report showed that wheat grain yields dropped an average of 4.2% for every 10 Italian ryegrass plants per square meter.

4. Henbit/purple deadnettle. Purple deadnettle is one of the most easily recognizable weeds. It’s often visible from roads as it covers spring fields with color.

Most of these annual weeds are flowering or past flowering and starting to die back on their own.

Henbit does not compete as much with wheat as some other winter annuals. However, it can cause yield reductions in high densities.

Bradley puts purple deadnettle in the same category.

“Research we conducted in several locations in Missouri years ago showed that season-long competition from henbit at densities of 18 plants per square meter did not cause any wheat yield loss at all,” he says. “However, densities of 82 plants per square meter reduced yields by 13%. The stage of growth that these species are in at the time you wish to treat is critically important.”

Herbicide applications might prevent seed production, but these weeds are not going to be competitive enough to make it an economically justifiable treatment, Bradley says.

Source: University of Missouri Extension, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.
TAGS: Herbicide
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