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Competency Area 1: Weed Management

PO 10. Demonstrate familiarity with life cycles and growth habits (dicotyledons and monocotyledons) of weeds and how these characteristics affect weed management.

Life cycles  
Annuals - complete life cycle in one year:
Summer annuals - germinate from seed in spring or early summer then flower and set seed before the end of the growing season, i.e. common ragweed and large crabgrass.
Winter annuals - germinate from seed in late summer or fall, then flower and set seed the following spring or early summer, i.e. corn chamomile, shepherd’s-purse and purple deadnettle.
Biennials - take two years to complete life cycle: They make vegetative growth the first year. Then after additional vegetative growth in the second year, they flower and set seed, i.e. common burdock and bull thistle.
Perennials - live for more than two years.  Perennials reproduce from seed only or from seed and vegetative organs. Perennial plant forms include:


Simple - from seed only, i.e. dandelion and curly dock.

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Bulbous - from seed, aerial and underground bulblets, i.e. wild garlic.

Tuberous - from seed and tubers at tips of rhizomes, i.e. yellow nutsedge.

Creeping - from seed and either stolons (prostrate stems or runners that root at the  nodes) or rhizomes (underground creeping stems). Rhizomes may be either shallow “rooted” (quackgrass and wirestem muhly) or deep “rooted” (common milkweed and horsenettle).

Growth habits are important because of herbicide selectivity and type/location of growing points (meristems).

Dicotyledons or broadleaf weeds have two seed leaves and apical/axial meristems so stem elongation is from tip(s).


Monocotyledons have one seed leaf and basal or intercalary meristems so stem elongation is from the lower portion of internodes.

Grasses have hollow round or flattened stems. The parts of grass leaves are:

Blade - part of a leaf above the sheath

Sheath - lower part of grass leaf that encloses the stem/younger leaves

Collar - outer side of a grass leaf at the junction of the blade and sheath

Ligule - thin membranous appendage or ring of hairs on the inside of a leaf at the junction of the blade and sheath

Auricle - a small projecting lobe or appendage found where the blade meets the sheath

Rushes have solid, round stems
Sedges have solid, triangular stems