A new weed has been identified in California rice. Its name is winged primrose willow (WPW), and it is a weed in rice fields in the southern US. So far this weed has been identified only in fields near Richvale. The Butte County Ag Commissioner is working to make sure this weed doesn't spread to other areas. The UC Davis Rice Weed Science Project and UCCE is collecting information about its biology, possible impact and management.

Don't confuse WPW with other waterprimroses, similar weeds that are usually seen around rice fields and ditches and are prostrate. WPW habit is erect, the yellow flowers have 4 petals, and the stem has wings or membranes that run longitudinally. Unlike other waterprimroses, WPW can grow within flooded rice fields, which makes it more problematic.

Here's what WPW looks like in the field

Flowers have 4 petals


Cross section of stem, showing "wings"


Fruit


This is NOT WPW, this is the waterprimrose that we usually see around field borders, notice the prostrate habit


This is NOT WPW, common waterprimrose flower has 5 petals


If you suspect you have WPW in your field, call any of the UCCE Rice Advisors or your Ag Commissioner.

Photos by J. Eckert and L. Espino.