Western agricultural concerns about weed cost increases center on the growing problem of herbicide resistance.

At the recent California Weed Science Society annual meeting in Santa Barbara, Calif., in the traditional* realm of weed control, Brad Hanson, UCCE weed science specialist, addressed the issue of off-site movement of herbicides, a growing concern because of heightened regulations to prevent ground and surface water contamination.

* The CWSS conference also featured a session on marijuana cultivation. See California’s growing marijuana business impacting agriculture

“Any herbicide that misses the target or moves from a plant treatment zone is off-target,” said Hanson.

Herbicides tend to be more persistent once leached below root zone, noted Hanson. To avoid off target movement, Hanson encouraged proper applicator training and equipment set-up. A full understanding of the impact of weather on off-target movement is also imperative.

Understanding the chemistry of the herbicide used is also critical, he added.

“Good agronomic practices, including irrigation, also help” to prevent off-target movement.

While the issue of water quality has quickly become the focal point of California’s regulatory oversight, it has been part of the California Department of Pesticide Regulation mandate since passage of a state law in 1985 to protect groundwater.

Murray Clayton, from DPR’s environmental monitoring branch, reminded growers, PCAs and others at the CWSS gathering of the groundwater protection zones DPR has identified from extensive well monitoring that uncovered unwanted pesticides in wells.

Some 5,600 wells have been sampled and unwanted pesticide residues were found in 1,500. Most, he said, were near cities. Some of these finds resulted in the banning of several fumigants, including DBCP.

Four years ago DPR expanded its list of known groundwater contaminants which require permits for use in groundwater protection areas. These are accessible via the DPR website. These permits require mitigation measures.

DPR has identified two soil properties most likely to contribute to groundwater contamination, coarse soils and hardpan.

DPR recommends that growers with hardpan improve soil penetration rates by improving soil conditions, thereby minimizing run-off.

For coarse soils, reducing leaching is the goal. This can be done by using sprinklers with an irrigation efficient goal of 80 percent. Micro irrigation also obviously reduces leaching, compared to flood or furrow irrigating.

Murray also said DPR recommends chemicals be applied after deep water irrigation for things like leaching salts or groundwater recharge, not before. Same goes for frost protection with water in citrus groves, orchards and vineyards.

California farmers spend a little more than $900 million annually on weed control, according to University of California agricultural economist Karen Klonsky.