Weed Updates 2024

General review of the year:

Walter's barnyardgrass AKA coast cockspur (Echinochloa walteri) continues to spread across the valley. Kassim AlKhatib and I continue to work on understanding more about the biology and management of this new weed, and will have more data coming in the future about its competitive abilities and tolerance for different irrigation methods.

A greenhouse screening shows it is resistant or tolerant to most of our registered rice herbicides. The herbicides still showing the greatest efficacy (alone) are: Cerano® (clomazone), Clincher® (cyhalofop), and SuperWham®/Stam® (propanil).

While field studies are being conducted to look at late-applied tank mix combinations or sequential applications of many registered rice herbicides, we currently have no species-specific data (between late watergrass, Walter's barnyardgrass, barnyardgrass, etc.) so recommendations would be the same regardless of the specific species found in a particular field.

For specific recommendations for your field, please submit samples to the UC Weed Science Research Herbicide Resistance Screening Program with Kassim Al-Khatib.

General control recommendations for all watergrass species are:

Best grass control:

• Abolish® + SuperWham®/Stam 80DF®

• Regiment® followed by SuperWham/Stam® (may cause injury on certain specialty varieties) Good grass control):

• SuperWham®/Stam 80DF® + Loyant® • SuperWham® /Stam 80DF® + Shark H2O® (some phyto)

• Regiment® + Clincher®

• SuperWham® /Stam 80DF® + Clincher ®

New weed species:

Eastern annual saltmarsh aster (Symphyotrichum subulatum var. elongatuma) is a perennial herb that is not native to California. It was found in a rice field in Colusa County this year, and has been found previously in 3 locations in Butte County (but not in rice fields).

At this point in time, there is no concern with finding this plant in a field, as it is not considered noxious. However, no herbicide recommendations are available at this time. It has been found in a field that is using no-till planting methods, and may be showing up there due to the selection pressure caused by no-till planting, which causes a shift from annual weeds to perennial weeds over time.

 

Figure 1. Eastern annual saltmarsh aster (Photo Credit: PictureThis).