UC Davis

E. tristachya (threespike goosegrass) is related to the more widely distributed Eleusine indica (goosegrass). While E. indica is a large stature and erect annual, E. tristachya is a tufted, low growing, perennial (or semi-perennial) grass of growing concern in California’s Central Valley orchard production systems. In response to reports from almond growers regarding difficult-to-control grasses, including E. tristachya, field and greenhouse research was conducted to address industry needs. In 2016-19, field studies were conducted in a walnut orchard in Chico, California, an almond orchard in Livingston, California and in a prune orchard in Orland, California to evaluate the efficacy of several pre-emergent (PRE) and post-emergent (POST) herbicide control options for E. tristachya. Orchard floor management programs generally utilize a winter PRE program to manage E. tristachya seedlings. In these experiments, single application treatments were compared to a sequential herbicide program composed of a winter application of indaziflam followed by a spring application of pendimethalin in order to target the phenology of E. tristachya. In separate experiments, POST treatments were made to evaluate control options for established E. tristachya stands. In 2018, greenhouse experiments were conducted to evaluate the efficacy of several POST herbicides on E. tristachya at two different growth stages. The trial design for field experiments was a randomized complete block with four replications. Winter PRE treatments were applied in January each year and the spring applications of pendimethalin, for the sequential herbicide program, were applied in March. Visual assessments for the PRE treatments were conducted at monthly intervals, starting one month after the January applications, and carried through to June. POST treatments were applied in May and control assessments were conducted at weekly intervals, starting one week after application, for five weeks. In both PRE and POST experiments, control of E. tristachya was estimated using a 0 to 100 scale, where 0 means no control and 100 means plants were completely controlled. The most efficacious control in the PRE experiments was obtained through sequential herbicide applications (SHA) of indaziflam followed by pendimethalin, which provided 88% control, five months after the initial treatment (MAT), across all three years at each site. The highest level of POST control was obtained with sethoxydim, clethodim, and fluazifop, which all controlled tillered E. tristachya greater than 73%, five weeks after treatment (WAT) at all sites. Glyphosate applied at a common field rate or twice that rate proved to be the least efficacious, with less than 51% control five WAT across all four years. The results from this study indicate that a properly timed and applied SHA, along with the use of POST graminicides, provides the greatest control of E. tristachya, while glyphosate provides poor management of this species.