Dandelions rearing their ugly heads – or not

Weeds can be tricky devils. All of us have seen instances in which pets – dogs, cats and other furry or finny friends – learn behaviors that help keep them out of harm’s way or earn them an extra chewy treat or belly rub.

I didn’t know weeds can also learn new behaviors until I read a press release published by the Weed Science Society of America the other day. In It, the WSSA announced it has coined a new definition for the term superweed.

The Society says superweed has become a catchall term used by many to describe weeds that are perceived to be more invasive and to grow more aggressively after developing resistance to herbicides. Most in agriculture would agree those words describe the increase of Palmer amaranth in many parts of the Sunbelt and now in the Midwest.

“Use of superweed has snowballed in recent years, along with considerable misinformation that isn’t supported by scientific facts,” the WSSA said. ”Most online dictionaries, for example, associate superweeds with herbicide resistance caused by the suspected transfer of resistance genes from crops to weeds.”

As the WSSA notes, no scientific evidence exists to indicate that crop-to-weed gene transfer is contributing to the herbicide resistance issues faced by farmers; i.e. genes that confer resistance to crops are not being passed along to weeds.

“Since superweed is now clearly part of the public vernacular, we decided to offer a definition that more clearly reflects the true source of herbicide resistance,” says Lee Van Wychen, Ph.D., WSSA science policy director:

“Superweed: Slang used to describe a weed that has evolved characteristics that make it more difficult to manage due to repeated use of the same management tactic. Over-dependence on a single tactic as opposed to using diverse approaches can lead to such adaptations.”

Besides the fact that activist groups appear to be trying to use catch phrases, such as Superweed, rather than scientific fact, in their efforts to set U.S. agriculture back 60 years, one of the most interesting facts in the release concerned weed behaviors.

Though the term superweed is most often associated with weeds resistant to one or more herbicides, WSSA scientists point out resistance can result from overdependence on mechanical, biological or cultural management tactics as well.

“Repeated hand-weeding of barnyardgrass growing in rice fields, for example, has led to weeds that escape control by mimicking the appearance of rice plants,” the WSSA said. “Similarly, spotted knapweed has become increasingly resilient to the gall flies used repeatedly as a biological control. Even dandelions growing in a regularly mowed lawn can evolve to avoid the mower, produce seeds and spread.”

So if you’ve been thinking those dandelions were dodging your mower, you’re probably right.

For more on the “superweeds” issue, visit http://wssa.net/wp-content/uploads/WSSA-Fact-Sheet-on-Superweeds_16-Sep-2014.pdf

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