In case you have wondered: A weed is a wildflower growing where it is not wanted.

"What is a weed? A plant whose virtues have not yet been discovered," Ralph Waldo Emerson

What is a Weed?

Bureau of Land Management
Environmental Education Homepage

Generally, the term weed is used to describe any plant that is unwanted and grows or spreads aggressively. The term exotic weed describes an invasive unwanted non-native plant. Terms such as invasive weed or noxious weed are used somewhat interchangeably to refer to weeds that infest large areas or cause economic and   ecological damage to an area. The term "noxious" weed has legal ramifications in some states that maintain official lists of noxious weeds. What is considered a weed   in one area may not be a weed in another.

Upsetting the Balance

Native plants evolved over millions of years to fill unique ecological niches. What we know as weeds today (non-native, ecologically damaging plants) did not exist in the wilderness then.

These plants developed in and are native to other countries. Like our native plants, they are kept in check in their native environment by insects or diseases and by competition with other species. In order to survive in their native ecosystems, many plants develop characteristics that make them especially hardy.

Early European settlers in North America inadvertently brought weed seeds with them, perhaps in the hay they brought for their animals or in the dirt they used as ballast for   their ships, or even in their clothes or bedding. Some activities, such as clearing the   land, opened up niches that created places for weeds to grow. Settlers also purposely brought plants from their "home country" to reseed areas, make dye for clothing, and use as ornamental plants.

Without their natural enemies, some non-native plants became invasive, reducing the diversity and quantity of native plants. Weeds are continuing to spread rapidly in many areas across the country. Weeds spread to an estimated 4,000 acres (over 6 square   miles) each day on public lands managed by the Bureau of Land Management (BLM) 
and the Forest Service. But weeds know no boundaries. They also are spreading on private and park lands. In fact, no one really knows how fast or how far they are spreading.

Looks can be deceiving

To many, invasive weeds are simply beautiful wildflowers. Some of them, such as purple loosestrife or wisteria, are favored by gardeners for their beauty and hardiness. But when allowed to escape into wild lands, they cause serious ecological and   economic damage to many areas.

Weeds take over important habitat areas for wildlife, devastating shelter and forage   while reducing the diversity and quantity of native plants. When weeds do not hold and   protect the soil the way native plants do, erosion increases, causing sediment in streams, which can hurt fish populations and water quality.

Weeds are often less resistant to wildfire than are native plants. Weeds also reduce and values, causing damaging economic impacts to local communities. For example, weeds have a profound effect on ranching and agricultural operations because they can reduce production of forage and crops.

Weeds are often thorny and scratchy, and grow in dense patches, which makes hiking   or other recreation activities difficult if not impossible. Weeds increase the cost of maintaining recreational facilities. Leafy spurge alone costs North Dakota an estimated $87 million a year. Weeds are a problem from coast to coast, ranging from invasions
such as kudzu, an aggressive Asian vine, in the Southeast, to knapweed, a tough, rapidly invading competitor, in the Northwest.

NUTSEDGE (NUTGRASS)

A SUMMER WEED IN YOUR LAWN OR LANDSCAPE

Sedges have an awesome ability to grow and multiply, having a triple threat reproductive system.  The umbrella like seed heads on the tops of the triangular stems contain thousands of seed, each capable producing  a new sedge plant.  Underground the plant produces lateral stems that spread in every direction, sprouting new plants along the way.  Along those stems are produced the peanut-sized "nuts" that give nutsedge its name.  If you try pulling nutsedge by hand, each of the nuts sprout and develop into more plants.

Nutsedge is not a grass.  Its a member of the same family as cattails, tulles and rushes.  These are plants that thrive on wet conditions, so if you have a nutsedge problem over watering the faster the nutsedge will spread.

MANAGEMENT

For area where there are no desirable plants nearby, use Roundup.  When spraying, follow the caution on the label. For those areas where nutsedge is mixed with the grass in the lawn a selective herbicide should be used. 

Manage:

Wicking with Roundup:  For a few plants you can brush on roundup use to the leaves of nutsedge. Being careful that you do not make contact with desirable plants for it will kill or cause damage.  Sometimes an apron around the nutsedge plant is needed for extra protection.

Begin treatment as soon as you see the first sprouts of nutsedge in the spring or early summer.  The sooner  you control the sedge , the less chance there is for seeds or nut to form. 

CRABGRASS

Crabgrass germinates in the springtime when the soil begins to warm and dies during  cold weather.  Crabgrass branches out freely, forming dense, unsightly patches that smother the turf.  Stems lie close to the ground, often rooting at the nodes, making crabgrass hard to reach with a lawnmower.

The first strategy is to use pre-emergent to prevent germination.  There are a variety of pre-emergent and herbicides for effective control crabgrass.