Location: Invasive Species and Pollinator Health
Project Number: 2030-30400-001-006-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2026
End Date: Aug 31, 2029
Objective:
The goal of this project is to improve understanding of the spread of Wingleaf primrose-willow (Ludwigia decurrens) and improve integrated weed management outcomes for this species. Although it was first discovered in the rice growing region of Northern California in 2011, periodic monitoring occurred for several years but recently this species has started to spread along the irrigation ditches and canals, and into grower fields where competition with yields is a concern. In addition to threatening crop yields, this pest has the potential to interfere with water delivery and natural resources. Surveying and recording the extent of the infestation is a critical first step in developing management strategies, as it increases the chances that targeted management approaches can be utilized.
Approach:
The cooperator and ARS will continue monitoring in Butte County where L. decurrens was first recorded in California and to perform monitoring in surrounding counties with reported occurrences (Shasta, Tehama, and Placer). Surveys will occur via public roads as well as kayak, boat, and canoe surveys in irrigation canals, rivers, and streams. New occurrences will be recorded, and a subset of samples will be submitted to herbaria and state agencies for genetic confirmation.
Objective 2. Based on initial greenhouse and field trials, there are several viable options for herbicide control of L. decurrens that would benefit from further testing and small-scale implementation by research teams, while scaling up in cooperation with irrigation districts and county agriculture commissioners’ offices. Organic rice farmers would additionally benefit from investigation of non-chemical control methods including mowing and hand pulling. Field applications will attempt to control L. decurrens in aquatic systems and rice fields using foliar and pre-emergent herbicides such as glyphosate, triclopyr, imazamox, and flumioxazin in comparison with cutting. Treatment areas will be monitored on a biweekly basis and reapplication consistent with label restrictions will be performed as needed.
Objective 3. Greenhouse and mesocosm screening will continue on L. decurrens, sourcing seed from infestation sites and the collaborator will focus on trials utilizing herbicides available in rice while the SY will focus on trials utilizing herbicides available in aquatic systems.