It’s been said that a weed is any plant that grows by itself in a place where people do not want it to grow. That probably covers a lot of plants in many of our yards. To be able to control weeds effectively, it helps to know what kind of weed it is. Fortunately, the University of California has good resources to help you identify weeds and then to manage them.
The Weed Gallery is the first place to start. It contains images of more than 150 of our common weeds. Start with the introductory page where you decide whether your plant is a broadleaf, grass, sedge, or aquatic plant. Click on Identification to see photos of different shapes of leaves that will take you to more photos of weeds with that shape of leaf.
Click on Tutorial which will take you to a page with illustrations that define plant parts and help with identification. Learn the differences between racemes and umbels or stolons and rhizomes.
If you think you know the name of your weed, go to the weed list where you can find weeds sorted by category. All have links to information and photos that will help with identification.
https://ipm.ucanr.edu/PMG/weeds_multi.html#BROAD
There is also help for identifying weeds in lawns at this link: https://ipm.ucanr.edu/TOOLS/TURF/PESTS/weedkey.html
Links to weed information
Weed photo gallery: https://ipm.ucanr.edu/PMG/weeds_intro.html
List of weeds and how to control them: https://ipm.ucanr.edu/PMG/menu.weeds.html
Weed Management in Landscapes: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7441.html
Weed Management in Lawns: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74113.html
Woody Weed Invaders: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74142.html
Help Desk of the UC Master Gardeners of Contra Costa County