Spring time in the Truckee Meadows: tomatoes are planted, iris is blooming, and weeds are growing. Our wet winter is paying off in weed dividends.
Many of the weeds sprouting and growing right now are annuals. They are best controlled early on in their life, before they bloom and set seed. Most are easy to pull when small. Pesticides (herbicides) can be used for control also, but use caution to avoid damaging adjacent plants or lawns.
Previous articles mentioned kochia and prickly lettuce; they are still out there and will be easy to control by pulling or spraying. Here are some other weeds to watch for as well.
Annual bursage grows to 3 feet tall. Its gray-green lobed leaves are covered in short, bristly hairs. This plant produces spiny flowers later on that stick to people and animals. Control it now by hand pulling or hoeing. The plant will regrow if mowed.
Annual sowthistle grows to 4 feet tall. Its leaves are hairless but have spines along the edges. The upper leaves of the plant clasp the stem, and the stems ooze milky sap when cut. The flower head is formed of numerous pale yellow flowers that form puff ball seed heads, resembling miniature versions of dandelion flowers and seed heads. Dig or pull young plants. Mowing is effective.
Common purslane is a prostrate succulent that can spread to 2 feet wide. Its teardrop-shaped leaves are similar in appearance to the common houseplant, jade. Flowers are very tiny and form where the leaves meet the stem. Dig, hoe or pull plants. It can re-root, so remove all pulled plant material. Mulching to exclude light can also be effective.
Spotting spurge and prostrate spurge are two plants considered to be the same species. It forms a prostrate, low growing mat. Stems exude a milky latex juice when broken. Dark green leaves are arranged opposite each other on reddish stems. Spotted spurge leaves have a reddish-to-purplish spot in the middle; prostrate spurge leaves do not. Both stems and leaves are hairy. This sneaky little plant invades lawns and gardens, avoiding the mower with its low-growing habit. It can go from a sprouting seed to a seed-producing plant in as little as 5 weeks, so there can be multiple generations per year. Pull, hoe or till the seedlings. Mulching can help prevent weed growth.
Common lambsquarters starts as a ground-hugging rosette. It grows to 5 feet tall and has light greenish-gray triangular or goose-foot shaped leaves. Leaf tops are covered in a whitish powder, and the undersides of the leaves are whitish. Stems are branched with purplish-red stripes. Dig, hoe or pull young plants. Plants usually don’t survive mowing or clipping.
Redroot pigweed grows to 6 feet tall. Its stems are hairy, and its lower stems and root are reddish. The plant’s lower leaves are oval, while its upper leaves are lance-shaped. The leaves have prominent veins and are attached to the stems by hairy stalks. Flower clusters have stiff spines. Pigweeds are a common cause of late summer allergies. Dig, hoe or pull young plants, while taproot is shallow. Mowing is not effective.
Like its cousin above, prostrate pigweed can have reddish lower stems and roots. It grows as a ground-hugging, 2-foot wide plant radiating from a central crown. Its leaves and stems are not hairy, and its leaves are oval with the tip broader than the base. Dig, hoe or pull young plants, while taproot is shallow. Mowing is not effective.
Russian thistle or tumbleweed is a bushy plant that grows to 3 feet tall. Its multi-branched stems are striped with red or purple. Young leaves are soft, green, fleshy and lack spines. Mature leaves are short and stiff, with sharp spines at the tip. This plant requires warm, disturbed soil to germinate, so avoid disturbing the soil unless you plant competitive vegetation or cover in mulch. Dig, hoe or pull young seedlings, before spines form.
All of these weeds reproduce by seed, and a single plant can produce thousands of seeds. Preventing seed production is essential. If you can’t pull plants now, cut off the seed heads later in the growing season. Note the area of infestation this year, and apply a pre-emergence herbicide early in the season next year.
Watch the weather when controlling weeds
It is tempting to want to eliminate weeds using pesticides, but you need to use caution during our warmer temperatures. Remember, pesticides are substances designed to kill something: herbicides kill plants. Spraying pesticides when temperatures are above 80 degrees F can pose a real hazard to you, your pets and livestock, the rest of your yard and your neighbor’s yard.
At temperatures above 80 degrees F, sprayed pesticides can volatilize, or turn to a gas. The pesticide can then drift to non-target sites, such as your landscape trees, the dog’s water bowl or the neighbor’s prized roses. Spraying during windy conditions can also pose a risk of pesticide drift.
Even lower risk pesticides, such as horticultural oils and insecticidal soaps, should not be applied when temperatures are above 80 degrees F. These lower risk pesticides can burn plant leaves if applied at high temperatures.
What can you do? First, READ THE LABEL. The pesticide label will tell you at what range of temperatures it should be applied. Most pesticides are labeled for application between 60 degrees and 80 degrees F. Remember: when you buy a pesticide, you are agreeing to READ, UNDERSTAND and FOLLOW the label directions.
Watch the weather reports. If there will be a cooling trend later in the week, can you postpone your spray application until then? Is it going to be windy, or is there a chance of rain? If so, you should not apply the pesticide that day. Can you spray early in the morning, when temperatures are cooler and winds are generally lighter? This will also help protect insect pollinators such as bees, who are not as active early in the morning.
Melody Hefner is the Urban IPM and Pesticide Safety Program Coordinator for University of Nevada Cooperative Extension. Have a gardening question? Contact a master gardener at firstname.lastname@example.org, or visit www.growyourownnevada.com.