Our wet winter has set us up for some spring weeding chores. Many of our nuisance weeds are annuals. Annual weeds complete their life in one growing season: sprout, grow, flower, produce seed and die. Winter annuals sprout in the fall, lie dormant through the winter and then start growing very early in the spring. Summer annuals sprout in the spring, then grow, flower, produce seed and die in the fall. For either winter or summer annuals, once they have formed a seed head, they have stopped growing and have begun to die. Applying herbicides when annual plants have formed a seed head is a waste of time and money. Annuals reproduce by seed only, so any control plan you choose has to include preventing seed production.
Many winter annuals, such as cheatgrass, flixweed, redstem filaree, tumble mustard and hare barley have already grown and are producing seed heads now. These plants should be pulled as soon as possible, before the seed disperses and increases your weed infestation next year. You cannot mow these weeds if they have seed heads, as mowing will sow viable seed into your landscape. You must pull and dispose of the plant parts, being careful not to disperse the seeds.
Summer annual weed seeds are starting to sprout right now. These weeds are best controlled as seedlings. Seedlings are easy to pull or hoe, as they have very weak root systems. The most difficult thing is to identify the weeds when they are seedlings. Here are a couple of common summer annual weeds that can be effectively controlled now with a simple tug.
Kochia: This annual weed has gray-green, lance-shaped leaves covered with fine hair. As a seedling it looks quite harmless, but the adult plant can reach 1 to 6 feet in height. It breaks off and tumbles in the fall, spreading seed as it moves. You can pull this plant easily when young, but it develops a deep taproot as it matures, making it difficult to pull. This plant can’t be mowed as a control method, as it will readily regrow from the root.
Prickly lettuce: This annual is sprouting up in lawns and other landscape areas now. The stems are prickly and can have a reddish cast. The leaves are prickly along the edges and on the undersides and may be deeply lobed. In summer it forms small, yellow, daisy-like flowers which then turn to small puff ball seed heads, similar to dandelions. Prickly lettuce has a deep taproot, so pull it while it is young. Like kochia, mowing is not an effective control since prickly lettuce will grow back from the roots.
If you elect to use herbicides, apply them during the seedling growth stage, when the weeds are small and tender. Mature plants are more difficult to control with herbicides.
Melody Hefner is the Urban IPM and Pesticide Safety Program Coordinator for the University of Nevada Cooperative Extension. Have a gardening question? Contact a master gardener at firstname.lastname@example.org.