Weed and vegetation control is done mostly during late summer on the Coast side and in June and July on the Bayside.  The County controls roadside weeds using a combination of mowing and spraying herbicides. 

Why do we manage roadside vegetation?

Weeds and grasses along roadsides create a fire hazard in summer and fall, can obstruct drainage ditches, potentially limit driver visibility, and can directly lead to the deterioration of roads if left uncontrolled.

How do we manage roadside vegetation?

Roadside vegetation is managed through a combination of mowing and the application of herbicides. The County generally mows or sprays a 3 foot to 5 foot width of roadway shoulders where grasses, invasive species and woody plants are found. Areas which are free of such vegetation do not require treatment.

Some County areas are not treated with herbicides. However, because mowing is so much more labor intensive than herbicide applications, we do not have the resources in “mow only” areas to properly manage roadside vegetation. In wet years, individual areas may need to be mowed as many as 4 times per year to be adequately controlled.

What herbicides do we use and when do we apply them?

San Mateo County uses the following herbicide products for vegetation and management:

  • For grasses: Roundup Pro or Finale
  • For woody plants : Milestone VM or Garlon

Herbicides are generally applied during dry weather periods between January and June. Prior to herbicide applications, San Mateo County posts notices at either end of roads that are to be treated. Information on products used by the County is included on its website.

How are herbicides selected and how do they work?

San Mateo County consults annually with a certified pest control adviser to determine appropriate herbicide products. All products are selected consistent with the County’s adopted Integrated PestManagement Plan, which strives to manage vegetation using environmentally sensitive strategies. All products selected for use must also be approved by the Environmental Protection Agency and the California Department of Pesticide Regulations. The herbicides work by cutting off the plants nutritional source.

How are herbicides applied and what training do County employees receive?

San Mateo County employees involved in herbicide application receive annual training on herbicide applications. Herbicides are mixed with water and applied with a specialized truck which is designed to apply herbicides precisely at programmed application rates. Depending on the products used, the concentration of herbicides range from approximately 0.1% (0.1 ounces per gallon of water) to 2.3% (1.17 ounces per gallon of water).