Weed Life Cycles and Control Strategies

Annual weeds 

Annual weeds have a one-year life cycle. They germinate, grow, flower, set seed and die in one year or less. They reproduce by seed only. Common roadside annuals include common ragweed and giant ragweed.

To control:

  • Mow prior to seed-set.
  • Eliminate bare soil and disturbances to vegetation.

Biennial weeds 

Biennial weeds have a two-year life cycle. In the first year a basal rosette (circular cluster of leaves on or near the ground) is produced. The second year a central flowering stalk elongates and the plant dies after seed maturation. Biennials spread only by seed. Common roadside biennials include musk thistle, bull thistle, poison hemlock, wild parsnip and wild carrot.

To control:

  • Mow prior to seed-set five consecutive years.
  • Treat rosette plants with herbicides in fall or early spring when results are typically the best and damage to desirable plants can be minimized. (Biennials become much more tolerant of herbicides after the stem has elongated.)
  • Establish native vegetation to deprive biennials of sunlight during their weak seedling stage.

Perennial weeds

Perennial weeds can live for a few years or for many years. Some perennials reproduce only by seed; many spread by seed and a variety of underground reproductive structures. Control of these perennials may be very difficult because of their extensive root systems.

To control:

  • Treat with herbicides.
  • Mow to prevent seed maturation and extend the herbicide treatment window.
  • Establish a diverse, native plant community.