May 2022  -  Weed Science Webinar Series Shifting Focus to Mechanisms

Beginning next week, the Weed Science Webinar Series, which is being hosted by the USDA's Agricultural Research Service (ARS) and the Weed Science Society of America (WSSA), will shift in focus from tactics of weed management to the mechanisms.

The three webinars will address basic research topics associated with how weeds and invasive plants are able to do what they do and why, which is key for developing sustainable management strategies. If we don't know the why and the how, then the way that we manage is often...

In 2017, I started getting reports of a watergrass biotype/species (Echinochloa spp.) that was difficult to control using our suite of herbicides registered in rice. At the time, I knew we had multiple herbicide-resistance in late watergrass (Echinochloa phyllopogon), so I initially just thought the resistant biotype was spreading, and had maybe gained resistance to additional herbicide modes of action. However, once I started visiting fields, it quickly became apparent that this was not late watergrass (phenotypically-speaking). It also did not appear to be barnyardgrass (Echinochloa crus-galli), although the Echinochloa species are notoriously difficult to identify, and phenotypically quite variable in...

A recent call about the poor control of marestail (horseweed, Conyza canadensis) to glyphosate (Roundup®) wasn't surprising, but that paraquat didnt do the trick was.  It turns out that there is multiple resistance to the materials.  If horseweed is resistant to glyphosate it is possibly going to be resistant to paraguat  which also means that hairy fleabane which has glyphosate resistance could also show resistance to paraquat.  A recent study reports on the increased Conyza resistance to paraquat (Distribution of Conyza sp. in Orchards of California and Response to Glyphosate and Paraquat, Moretti et al, 

From the Topics in Subtropics blog ∴ June 15, 2016

Researchers have now confirmed that six glyphosate-resistant weed species have been identified in California. Four have been known to exist for some time; they are horseweed (marestail, Conyza spp.), hairy fleabane, rigid ryegrass and annual ryegrass. To that list, junglerice and Palmer amaranth in the Central Valley have been recently added to the list. Additional weeds that have become more of a challenge to control and are on the suspect list are goosegrass and, in the central San Joaquin Valley, the summer grasses sprangletop and witchgrass.

There have never been a lot of...