Our wet spring continues to produce weeds. Here are some troublesome annual weeds that start small and grow low. When they occur in lawns, their growth habit lets them avoid the mower. It also allows them to hide longer, increasing their chances of producing seed.
Common Purslane: This plant has smooth, fleshy stems and succulent, shiny, tear-drop shaped leaves that are wider at the tip than at the base. Stems grow prostrate, not upright. Leaf edges and stem may have a purplish cast. It blooms in summer, forming small, yellow, flowers with five petals. It will form a dense mat in moist areas. This plant is very persistent. It can re-root from individual leaves, so if you try to control it by physical removal, you must be sure to get all the leaves.
Spotted and Prostrate Spurge: Both plants grow prostrate, forming a thick mat. Leaves are small and oppositely attached to stems. Spotted spurge has one large purplish spot in the middle of each leaf, while prostrate spurge has no spot. Stems exude a milky latex juice when broken. This latex is toxic to animals and can be a skin irritant, so wear gloves when pulling. The small white to pinkish flowers are hard to see. This prolific weed can go from a germinated seed to a plant producing seed in as little as five weeks. Control of those first few seedlings can prevent a serious infestation, as this weed can have several generations in a growing season.
Prostrate Pigweed: This low growing weed has purplish fleshy stems that radiate out from a central taproot. Leaves are oval and one-half-inch wide, with the tip wider than the base. Flowers are small and difficult to see. It tends to grow in disturbed or cultivated soils and is a common garden weed.
Large Crabgrass: During early growth stage, this grass grows prostrate, avoiding the mower. Stems are thick and have a reddish color at their base. The prostrate stems can root where they contact the ground, helping the plant spread. The seed head may grow upright but is generally also prostrate.
Puncturevine: Also called goathead, this prostrate plant will form a mat of trailing stems. It produces flowers and seed continuously throughout the growing season. Leaves are oppositely attached to the stem and hairy. Individual leaflets are tiny and arranged in four to eight pairs along the stems. The plant forms yellow five-petal flowers and a woody bur that breaks into five sections at maturity. Each of the seed sections have two spines that radiate out from the seed pod in the center, giving the appearance of a goat’s head. The spines on the seed pods can damage bicycle tires, injure animals and are extremely painful to bare feet. Unlike the weeds mentioned above, puncturevine is a state-listed noxious weed. That means if it is growing on your property, you are required by state law to remove it and prevent its spread. Bag up plant parts and dispose of them in the trash.
Seeds of all of these annual weeds can remain dormant in the soil for years, waiting for the right conditions to germinate. They can easily take over, so pull the seedlings you see now before they have a chance to produce seed. For areas of previous infestation, preemergence herbicides can help prevent seed germination.
Melody Hefner is the Urban IPM and Pesticide Safety Program Coordinator with University of Nevada Cooperative Extension. Have a garden question? Contact a master gardener at firstname.lastname@example.org or 775-336-0265.