Weeds can be classified broadly as annuals, biennials, and perennials. Annual weeds complete their life cycles in 1 year; that is, they grow vegetatively, produce flowers and seeds, and then die usually in one growing season. Strict summer annuals have all of their growth activities in one crop-growing season and have no means of survival from one year to another except by production of seeds. Winter annuals germinate in the fall, pass through the winter as seedlings, and produce most of their growth and seeds in the next growing season. Winter annuals often may be perceived as being biennials
- Annual weeds are the most frequently encountered weeds. Common summer annual weeds are crabgrass, foxtail, lambsquarters, pigweed (amaranthus), common chickweed, ragweed, purslane, morning glory, and galinsoga. Some winter annuals are common chickweed, wild mustard, shepherd’s purse, and annual bluegrass. Some of these species behave as summer annuals as well as winter annuals.
- Biennial weeds complete their life cycles in 2 years. In the fist year, the growth is only vegetative as rosettes, and in the second year, the plants grow vegetatively and then flwer and produce seeds. Wild carrot (Queen Anne’s lace) and wild mullein are common biennials
- Perennial weeds live vegetatively in the soil for 2 or more years. They may flower and produce seeds in the fist year. Perennial weeds often have some flshy storage organs (roots, tubers, rhizomes, bulbs) that enable them to live from one year to another and often to propagate asexually. Perennial weeds because of their storage organs are harder to control by cultivation than annual or biennial weeds. Some common perennials are dandelions, docks, quackgrass, thistle, milkweed, nutsedge, and johnsongrass