Most of the summertime weeds we spend so much time trying to control in the Central Valley are well-adapted to heat, dry conditions and poor soil. Spotted and prostrate spurges, purslane and dandelions can survive quite nicely with little water in hardpacked soil and intense heat. This summer, though, we’re seeing a proliferation of weed types that require damp soil. Dallis grass, white clover, English daisy and yellow wood sorrel are far more prevalent than in other years.
There are two reasons for the increase in weeds that thrive in wet soil. During the last four severe drought years with mandated watering restrictions, all weeds produced larger amounts of seeds; many of those seeds did not germinate but remained viable on the dry soil surface during the drought (a survival mechanism). Above-average rainfall last winter followed by a wetter, cooler spring fostered the germination of those dormant weed seeds in the big bare spots in our formerly brown dead lawns. Also, a lot of homeowners who longed to see lush green grasses around their homes have begun to increase watering times or even ignore the mandated watering schedules and are now overwatering their lawns.
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With warnings now about the possible carcinogenic effects of glyphosate (the active ingredient in many post-emergent herbicides including Roundup), we should reconsider discontinuing or modifying our chemically-based weed control programs. Here are the labor-intensive, not as thorough, but environmentally safer controls for the new weeds on the block:
Dallis grass – It forms fairly large clumps in low, wet areas. The grass blades are coarse, dark green and stand almost upright. Use a spading fork or spade to dig up clumps and all the rhizomes (root structure), replace and level soil, and mulch bare spots heavily until reseeding the lawn in fall.
White clover – This used to be included in grass seed mixes. It goes dormant during drought, creating bare spots which have now filled in with clover. White clover is extremely hard to eradicate since it spreads by aggressively-growing, above- and below-ground stems.
If you’re worried about bee stings on paws and bare feet, try painting the plants with a post-emergent herbicide.
English daisy – I like seeing the white daisy flowers in a lawn, but many lawn purists don’t. Dig out the fleshy roots in spring and adjust irrigation sprinklers and timers to keep the lawn on the dry side. Don’t overirrigate.
Yellow wood sorrel – The bright yellow flowers of wood sorrel, also called oxalis, stood high and tall in many uncultivated areas this spring. If oxalis is not mowed or pulled in spring before seed pods form, the dry pods will shoot seeds into the neighbors’ yards when touched.
Look for the bronzy/green clover-like leaves and dig or pull the plants out. A vigorously-growing lawn will outcompete oxalis.
Send Elinor Teague plant questions at firstname.lastname@example.org.
For help identifying the weeds in your lawn, check the University of California’s Weed Photo Gallery: ipm.ucanr.edu/PMG/weeds_intro.html. It’s important to know exactly which weeds you have before buying and applying preemergent herbicides next fall or spring to prevent weed seeds from germinating.