Broadleaf weeds are easiest to identify. Like dandelions and clover, they are distinctive from and not botanically related to grasses and sedges. As the name indicates, Broadleaf weeds have leaves that are broad, and are generally produced in pairs or multiples. Leaves are detached from the main stem by a sub-stem or petiole. Leaves may be simple with one leaflet like dandelion. Or they may be compound having more than one leaflet like clover. Veins within the leaf give a netted appearance in most cases.
Grassy weeds, like crabgrass, are botanically related to lawn grasses. They have a similar appearance and development. Leaves of grasses are not detached from the main stem, but are narrow with a blade-like appearance. The leaves are produced one at a time in two vertical rows with veins within leaves that run parallel. Stems are usually round or flat. Since grassy weeds are often difficult to control once established in the lawn, they are generally best controlled with preventive or pre emergence herbicides. Pre emergence herbicides need to be applied before germination, as they act by preventing establishment.
Sedges, like nutsedge, have leaves that are similar in appearance and are often mistaken for grasses. Since herbicides used to control grass weeds are generally not effective on sedges, it is important to distinguish between the two. Sedges have two key identifying characteristics: leaves arranged in three vertical rows and a triangular stem. Stems of grasses are commonly round or flat with leaves in two vertical rows.
Summer annuals complete a life cycle within 12 months. Summer annuals usually germinate in the spring, grow or develop during the summer, produce seed and die by the fall or after the first killing frost.
Winter annuals complete a life cycle in 12 months but generally overlap two calendar years. They germinate in late summer to early fall and then begin to develop. Remaining dormant or semi-dormant throughout the winter, they flower the following spring then mature and die in late spring or early summer. Summer and winter annuals reproduce and spread by prolific seed production, becoming a ready source of infestation and establishment when conditions are favorable.
Perennials live for more than two years and may regenerate indefinitely. A simple perennial, like dandelion, may germinate from seed but produces a tap root that, when severed, can produce a new plant. A complex perennial can spread by seed as well as creeping above or below ground vegetative structures capable of bringing forth a new plant. Perennial weeds are often the most difficult to control mainly because they are an established plant that has already produced considerable vegetative reproductive structures. Repeated control measures then become necessary. Removing the above ground shoot growth does little toward long-term control. Herbicide treatments that act on the above and below ground structures are required for long-term control.