4 minute read
Weed control for common California nussance
THE SECRET'S IN THE SCIENCE WICK WIPER AND ROUNDUP OFFER GOOD MANAGEMENT OF COMMON RUSH/WIREWEED IN IRRIGATED PASTURES IN CALIFORNIA
by Ranjit Riar, Ph.D., Dept. of Plant Science, Jordan College of Agricultural Sciences and Technology, California State University, Fresno
Many California irrigated pastures are infested with common rush (Junucus effusus L.). Also known as soft rush or wireweed, it is a perennial weed that is easily spread by wind and irrigation water carrying the seeds from established plants in or near the irrigation network. Once established, it grows about three feet tall, with wide dark green clumps. Cattle tend to stay away from areas of the pasture with heavy infestation. Seed shed from mature rush plants, and new seed introduction with canal water can continue to increase the density of the weed. This reduces the quantity and quality of forage available for the cattle grazing on these pastures, and decreases their carrying capacity. Although this plant has other ecological applications, it is considered a weed in irrigated pastures.
Tillage and subsequent reestablishment of pasture is a costly control method, and the heavy seed bank left behind after tillage or mowing will allow the weed to re-establish and reduce pasture productivity. Seeds shed in the pasture can remain viable for decades, so reestablishing the pasture will not fix this problem. In this situation, herbicide application with a wick wiper can be an effective management option.
A research trial was set up on the Fresno State University Agricultural Lab irrigated pasture during the summer of 2019. Roundup® solution at 25 percent, 50 percent and 75 percent concentration was applied using a wick applicator pulled behind an ATV, using a single pass, and compared with an untreated control. Chlorosis, necrosis and weed mortality were evaluated at three days, seven days, 14 days and 21 days after treatment. Later evaluations were also done at six months and 11 months after the treatments.
Roundup is a systemic herbicide which moves within the plant after the foliage is moistened with the herbicide solution using wick wiper. This is a better option than spraying, as a few drops of Roundup can kill the entire grass plant on which those drops fall due to drift or bouncing off. Due to systemic activity, over time, roundup was able to kill large clumps completely (see pictures). Roundup takes about 14 days to kill a grass plant completely, but that time was longer for common rush. Maximum average chlorosis (yellowing 30 California Cattleman November 2020 or lack of green color compared to control) was 47 percent after 11 days for 50 percent treatment and 50 percent after seven days for 75 percent treatment. Higher concentration of 75 percent led to a quicker yellowing, but did not differ in overall control. Necrosis (dead leaf tissue) was noticed 11 days after application for all treatments, and reached values of 38 percent and 90 percent for both 50 percent and 75 percent solutions at 1 and 6 months after treatment, respectively.
The bottom line is that if a clump of wireweed/rush is coated with 50 percent solution by wiping with a wick, it will be mostly dead within six months, and completely dead within a year (see pictures). Once these clumps die, pasture grasses from surrounding areas will begin to grow in those spots, and patches of the pasture encroached by common rush can be reclaimed by desired grass species.
A word of caution using the wick wiper is that do not moisten the wick too much. The herbicide solution will begin to drip on the vegetation in the pasture, instead of being
transferred to the foliage of weeds contacting the wick. Any forage plant where these drops land will die. Prime the wick pump only enough to keep the wick moist, but not dripping wet.
Applying roundup with wick applicator to the pasture every few years on tall common rush clumps can be a suitable option for keeping wireweed under check, and maintaining the productivity of the pasture without costly tillage and re-seeding options.
This research was supported by Fresno State Ag Lab, Randy Perry, Ph.D., Beef Unit, UAL staff, and students supported by the LSAMP program.
Reduced competition from dead weeds allow forage grasses and legumes to fill in areas previously encroached by common rush/wireweed six months after wicking.
Dead common rush six months after treatment. Black arrow marks untreated plant from adjacent plot.
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