Summer annuals germinate in the spring and set seed in late summer or fall. Summer annuals thrive when summer annual crops like corn or soybeans are grown. They compete directly with the crop for resources. Biennials live during two growing seasons. The first year consists of vegetative growth, while the second year involves both vegetative and reproductive growth.
Biennials also reproduce from seed.
Because these weeds require two years to complete their life cycles, they are found in areas of low soil disturbance such as waterways, pastures, alfalfa, and fence rows. Perennial plants live for more than two years. Reproduction can occur by seed production or vegetatively by structures such as rhizomes, tubers, bulbs, or budding roots. Although perennial weeds are most prevalent in areas of reduced soil disturbance, some are well adapted to row crops. Managing perennial weeds is generally more difficult because of their multiple reproductive systems.