As spring nears, soil temperatures begin to warm up and many early spring weeds like cheatgrass, bulbous bluegrass, annual mustards, knapweeds, thistles, and leafy spurge begin to emerge. These weeds and many others are fast growing and take advantage of warm days and early moisture. Many times they have germinated, grown, and set seed before they are even noticed, especially the annual weeds. Rapid identification of these weeds in rangeland pastures during the seedling stages is the first step in the design of a successful weed management program.
Why would identifying weed seedlings be key in an overall weed management plan? Spring is an excellent time to control weeds because of their small nature and to keep them from producing seed, which means there will be less of a seed bank in the soil in future years. Each spring, plants are either beginning to grow from perennial roots or seeds. These tender, rapidly growing plants are quite susceptible to mechanical treatments and weed management is much easier, less costly, and more effective in the seedling stage than on mature plants. Also, controlling weeds during the early growth stages allows desirable vegetation to take advantage of more available nutrient resources. This improves overall plant community vigor and health.
When identifying broad-leaf weed seedlings, it best to first identify the shape of the cotyledons, which are first leaves that emerge from the soil. Sometimes the cotyledons are referred to as seed leaves. These leaves do not always persist and may not be present; however if seedlings have only reached the two leaf stage, cotyledons should exist. There are many shapes that can be seen, including heart, oval with a narrow tip, kidney, linear, lance-shaped, oval, oblong, egg-shaped, round, and pear-shaped (obovate).
Step 2 involves identifying whether the first two true leaves are opposite or alternate. Opposite leaves attach themselves at the same spot on the stem; alternate leaves do not and the newest leaf is typically smaller than the older leaf. After these characteristics have been identified, looking at true leaf shape, surface texture, growth habit (annual, perennial, or biennial), and leaf edge characteristics can help further identify the weed species. Consider contacting your local Extension Office for more information.
After the weed has been identified, one can then choose the appropriate control method. It is recommended that to achieve maximum long-term control many “small tools” be used. Often managers rely on one or two “large tools” such as tilling or chemical. These practices typically only provide short-term control of weeds. Long-term management refers to learning and adapting practices to manage weeds in the most responsive manner, using multiple appropriate techniques, such a combination of mechanical, chemical, biological, proper grazing management, and other cultural controls.
Weeds are well adapted to colonize and compete with desired vegetation. By using early detection and developing a weed management plan the impact of these invasive species can be mitigated. So as spring nears and soil temperatures begin to warm up, taking some time to be on the lookout for weed emergence and applying the proper control method will help improve rangeland pastures.