Weeds compete with crops for water, light, space, and nutrients and can significantly reduce crop yields through this competition for resources. In general, weed management is more important in the earlier part of the crops life. Crops tend to be more vulnerable to the effects of competition when they are establishing, and some have critical weed-free periods defined. Weeds can also harbor insects and diseases, as well as interfere with harvesting and other farm operations. Weed management options include physical, cultural, and chemical controls. For most growers, integrating these three options provides the best overall control of weeds.
Weed control focuses on stopping weeds from establishing, eradicating weeds that have established, and preventing weeds from making seeds which will add to the soil seed bank and create increased weed pressure in the future.
Weeds are not all equally competitive. It can be helpful to prioritize weeds by their impact to the crop or their potential to spread aggressively when planning weed management. Proper identification of weeds can be crucial to successful control. Different types of plants (grass, broadleaf, rush, or sedge) respond differently to different controls strategies. Understanding the weed life cycle is also important to select the most effective timing of the control.
Weed Life Cycles
Annual plants complete their life cycle in one year and reproduce by seed. They germinate from seeds, grow to maturity, flower, and make seeds all within a single growing season. Biennial plants take two years to complete their life cycle. They typically germinate from seeds and grow vegetatively in the first year, then enter a period of dormancy over the winter. They flower and make seeds during the following growing season. Perennial plants can live for many years and may reproduce by seed, runners, rhizomes, etc.
Farm practices can impact weed populations on your farm. For example, growers who practice no-tillage or reduced-tillage will typically see the type of weeds shift from annual weeds to perennial weed species. Weed maps of field areas are extremely helpful in planning weed control strategies. A weed map can illustrate problem areas so that growers can target specific problems in specific areas, and help plan for future crop rotations. A weed map can also indicate shifts in weed pressure if kept continuously over years and indicate the possible need for a strategy change.