Nancy Garrison, Former Urban Horticulture and Master Gardener Program Coordinator with U.C. Cooperative Extension

What kinds of weeds are prevalent here?

The most prevalent ones are: dandelions, mallow (also called cheese weed), spotted spurge, crabgrass (distinctly different from the perennial bermuda, which is may also be considered a weed in many situations, field bindweed, and creeping wood sorrel.

In my experience, the most troublesome weed is the perennial creeping wood sorrel found everywhere in the cultivated, irrigated garden. It grows in a low creeping manner and forms roots where it's stem comes in contact with the soil.

The most important management technique is to never let weeds get established. Remove all weeds before they go to seed.

Weed blocking fabrics typically called landscape fabrics are very effective for suppressing annual weeds if applied to ground after existing weeds are removed and before new ones have emerged or gotten sizable. Perennial weeds may push through before their energy reserves are exhausted so less effective for many of them. These weed blocks work by limiting light needed for weed growth. They are far superior to black plastic because they are porous, letting water and air to pass through them, which minimizes root and provides a more hospitable environment for roots.

Soil solarization is definitely effective in killing most weeds in the garden but has limited practical application  It can only be used in full sun areas that can be cultivated, leveled and kept out of cultivation for 6-8 weeks from late June through early August. For more information on soil solarization, refer to the UC Library article (pdf).

Glyphosate (products such as Round-up or Glyphomax) is very effective to control certain perennial weeds which are otherwise difficult to manage such as find bindweed, bermudagrass, dandelions, and Bermuda buttercup, but should be the last resort. It should be applied toward the end of the active growing season of the particular weed, but before it has begun to die down. For Bermuda this would be September or October, for Dandelion it would be in spring before seeds develop (before you can blow them to the wind) and buttercup in April. The weed to be sprayed should be watered rather than drought stressed to most effectively move herbicide down into roots. Be aware that glysophate is a non-selective weed killer and as such it will damage or kill any plant it comes in contact with even if it just a light mist from the material drifting in a slight breeze. You can never be too cautious in avoiding drift to non-target plants nearby.

It is very tricky to recommend pre-emergent herbicides to home gardeners even though if applied at the proper time they can be very helpful. I strongly recommend our UC publication called Weed Management in Landscapes Pest Note 7441 which is free off our website at www.ipm.ucdavis.edu along with a number of other pest notes on specific weeds including: dandelions, creeping wood sorrel, purslane, annual bluegrass, field bindweed, spotted spurge, and bermudagrass.

Posted: 15-Nov-2003