The characteristics of a weed are that it appears attractive, desirable, or harmless but can weaken and kill native vegetation. (Then can't our native plants also be weeds?) It can be toxic, painful, or otherwise injurious to humans or animals, increase soil erosion and associated water quality problems, multiply itself rapidly, and generate tons of itself in a matter of months. It spreads naturally in water, wind, or soil, it is also spread by wildlife, livestock, and recreationists. Effects are not usually apparent until it is already out of control because it can lie dormant and unnoticed for years then reappear and spread.

      Then what is a weed? Consider this definition: "A weed is any plant which interferes with the management objectives for a given area of land (or body of water) at a given point in time."

      Who sets those management objectives? In the urban setting, it is the individual homeowner. To one person, a single dandelion in the front yard may be one too many, whereas the neighbor may feel comfortable with a lawn full of these bright yellow flowered plants. The level of weed management is going to depend, in part upon the management objectives established for a given property.

      What are some of the characteristics which transform ordinary plants into weed plant?. Few plants have the characteristics that make them true weeds. Of the total number of plants in the world (about 250,000 species), only 3% or 8,000 species are thought to be weeds. Of these, about 250 or 0.1% of the total are recognized as major problems in world agriculture, and only about 0.01 % or 25 species cause the major weed problems.

Here are ten weedy plant species that you should be able to recognize. Notice that they are mostly grasses or sedges. This then raises the question of using ornamental grasses in landscaping. Will they also become weeds in time?

• Cyperus rotundus, Purple Nutsedge;
• Cynodon dactvlon, Bermudagrass;
• Echinochloa crusgalli, Barnyardgrass;
• Eleusine indica, Goosegrass;
• Sorghum haleoense, Johnsongrass;
• Portulaca oleracea, Common Purslane;
• Chenopodium album, Common Lambsquarters;
• Digitaria sanguinalis, Large Crabgrass;
• Convolvulus arvensis, Field Bindweed;
• Cyperus esculentus, Yellow Nutsedge.

Characteristics of Weeds

Consider some of the characteristics which make weedy plants so competitive, persistent, and pernicious.

• Number of seeds per plant: Weeds are producers of large number of seeds. For example: Barnyard grass, 7000 seeds; Common Purslane, 52,000 seeds; Common Lambs quarters, 72,000 seeds; Redroot Pigweed, 117,000 seeds; Russian Thistle, 200,000 seeds.
• Seed dormancy: Dormancy is the ability of seeds to remain viable in the soil for extended periods of time. For example: Johnson grass, 20 years; Field Bindweed, 20+ years; Common Lambsquarters, 40 years; Redroot Pigweed, 40 years;
• Special Adaptations or Appendages: Some plants have developed means to assist in their spread and distribution, these include: Hooks and spines - sandbur, puncture vine; Pappus (parachutes) - musk thistle, milkweeds; Being Pretty - spotted knapweed, hoary cress, Dalmation toadflax (Linaria sp.).
• Vegetative Reproductive Capabilities: Vegetative reproductive structures are those asexual portions of the plant which allow for new plants to arise without flowering. Examples include the following: Roots with adventitious buds -Leafy Spurge & Canada Thistle; Rhizome - Johnson grass & Bermuda grass; Tubers - Yellow & Purple Nutsedge; Crowns - Dandelions & Plantains; Stolons - Bermuda grass; Special Characteristics: "Having a greater will to live."

     learn the correct name of the plant, either common name according to ones locality or scientific name
     learn about the plant and it’s characteristics, such as:
     Life cycle - annual or perennial.
        Are there different principles involved when dealing with an annual versus a perennial? How does it spread and reproduce? How does this affect the management plan? Find out if a particular herbicide can be used to manage the problem.
    Is it a grass or is it broadleaved?
        Grasses which are characterized by a single embryonic leaf (monocot), fibrous root systems, and parallel veins on the leaves.
        Broadleaved plants have two embryonic leaves (dicot), taproot systems, and a netted leaf venation.
    Each of these two general groupings have been further subdivided into classes according to their life cycle, which begins with the germination of the seed, is followed by vegetative growth, and is completed with the maturation of the seed. Time of germination and means of spread and reproduction help to create a more clear picture of the different classes of weeds encountered.

        Annual weeds - those that complete their life cycle in one year. This group of weeds has been further subdivided according to its time of germination into the following groups:
            Winter Annual - these are those weeds which germinate in the fall of the year, mature and set seed in the spring of the second year. Examples of winter annual weeds include: Rescuegrass; Wall or Little Barley; Annual Bluegrass; the Mustards: Flixweed, Tansymustard, Shepherdspurse, London Rocket.
            Summer Annual - those weeds which germinate in the spring of the year, mature and set seed in the same year. Examples of summer annual weeds include: Barnyardgrass, Crabgrass, Field Sandbur, Foxtail, Stinkgrass or Lovegrass, Common Purslane, Common Lambsquarters, Kochia, Pigweed Species, Puncturevine, Prostrate Knotweed, Prostrate Spurge, Russian Thistle.
Their only means of spread and reproduction is by the formation and dispersion of seed. This means - don’t let them set seed. Any management plan is going to have to deal with multiple germination, since these weeds will germinate in the soil whenever the conditions favor the process. Once you have managed the first flush of annual weeds, through cultivation, etc., there will be another group of seeds waiting.

        Biennial weeds - these are those weeds which take two years to complete their life cycle, or they live two years, and, are often, referred to as short-lived perennials.
            Examples of biennial weeds include:
                Musk Thistle - a true biennial with it’s rosette of leaves the first year, followed by the bolting of the seed stalk, flowering, and seed set during the second year.
                Common Mallow - is another biennial, but in this case the plant does not produce a rosette of leaves followed by bolting, rather it has a life span of two years.
            With biennial weeds the management principle is the same as with the annual weeds since their only means of spread and reproduction is through the formation of seed. Not letting the plant set seed is what is required if these types of plants are to be effectively managed.

        Perennial Weeds - these are the plants which have the vegetative reproductive structures. Control of these weeds requires not only stopping their seed production, but also the managing the vegetative structure under the soil, or above the soil in the case of the stolon. Like the annuals, the perennial weeds have been subdivided into two groups, but not according to their time of germination, rather according to their type of root system.

            Simple Perennial - these plants are capable of coming back year after year from the same root, but there is no underground lateral branching. Examples of simple perennial weeds include: Dandelion, Plantain.

            Creeping Perennial - these plants are capable of coming back year after year from the same root system and also have the creeping vegetative reproductive structures.

      Examples of creeping perennial weeds include: Bermuda grass, Johnsongrass, Nutsedge - Yellow and Purple, Creeping Woodsorrel, Creeping Chafweed or Khakiweed, Field Bindweed, Silverleaf Nightshade, Texas Blueweed.

     The management of weeds involves taking the time to consider all of the options available. This has been referred to as Integrated Pest Management. Consider this definition and see if it applies to the management of weeds.
     "A control strategy in which a variety of biological, chemical, and cultural control methods are combined to give stable long-term pest control at levels below those causing economic injury."

     That definition has some of the same central themes that our definition of weed had, that of the establishment of economic injury levels. It is the homeowner who will determine the level to which they will allow injury, whether real competition, death, or aesthetic.

• Biological Weed Management - the use of living organisms to manage or control other living organisms. Examples of this form of management include: You and me - all weeds are edible once, some will just kill you after you have eaten it. Puncturevine weevil - for the management of puncturevine. Geese - manage grassy weeds in strawberries.
• Chemical Weed Management - the use of herbicides. They are a member of the "total options" package for the management of weeds.
• Cultural Weed Management - with this type of management, the central theme is "giving the turf, or turf situation, the competitive edge". It is important to remember that "Weeds are not the cause of poor turf, but rather the result". Taking time to manage the other components of turf and turf situation management will allow the turf to be more competitive. Consider this, if a weed is removed form a turf site, unless the turf is healthy and competitive, what will take the place of that removed weed - another weed.
• It can not be stressed too much the importance of allowing the turf to be competitive through such factors as: Correct irrigation practices; managing the fertility; mowing the correct height; keeping diseases and insects under control; etc.
• Educated Weed Management - using all the available tools at our disposal. Whether it is the use of herbicides, identification of the weed species, or how to establish a mulch for the management of perennial weeds, the presentation of accurate information is critical.
• Mechanical Weed management - this is the physical removal of the weedy species. Examples of this form of management include:
•      Cultivation - with cultivation there are a couple of questions that need to be considered: How effective is cultivation going to be on the management of annual weeds? Answer: Quite good if the weeds are small. How effective is cultivation going to be on the management of perennial weed? Answer: Quite poor - because cultivation assists in the spread and dispersal of these weeds through the breaking up and movement of the underground vegetative structures.
•      Mowing - How effective will mowing be on the management of puncturevine? Answer: Poor due to the prostrate growth habit of this particular plant. How effective will mowing be on the management of sandbur in the pre-seed head formation stage? Answer: Fair, if the flowering stalk is erect and not prostrate on the turf. Can we use mowing as a means of spreading weeds? Answer: Yes, we do it all the time with dandelion when we mow our lawns when the plant is flowering with it’s white balls of seeds.
•       Hand pulling – Plowing
•       Mulches - the use of mulches, both living and nonliving, can be quite effective in the management of annual weeds. If using a mulch program to management perennial weeds, the effort may be futile unless the entire patch of perennial weeds is under the mulch. There are good descriptions on how to establish a mulching program for the management of weeds in the publications listed at the end of this section.
•       Preventive Weed Management - this type of management involves keeping the weeds out from the very beginning. It requires the homeowner to be actively involved in the recognition of the common weedy species and a desire to keep them out of their turf situation. There are several ways this can be done, here are a few examples of how weeds can be kept out of the turf situational areas:
•       Certified seed - when establishing a turf area using seed rather than sod, make sure the seed is certified weed free.
•       Clean along fence rows - weeds can and do move through and under fences. It is much easier to manage the weeds outside the turf or garden area.
•        Clean weeds along ditches - weeds are not afraid of the water and are also good swimmers.
•        Watch your topsoil source- if establishing a landscape that requires the addition of topsoil, consider where that topsoil is coming from. It may be coming from an area that is heavily infested with perennial weeds, which means those vegetative structures may be getting a free ride into your yard.

• Downy Brome: Soft leaf texture, hairy; Drooping, open seed heads
• Mustards: Flowers in the shape of cross.
• Flixweed: Finely divided leaves. Flowers, yellow. Seedpod with single seeds, one on top of another. Nontoxic species.
• Tansymustard: Similar to flixweed. Flowers are yellow. Short, stubby seed pod, seeds in pairs. Toxic plant.
• Shepherdspurse: White flowers. Seedpods are flat, heart shaped, narrowing to a point at the base.

• Sandbur: Characteristic spiny seed pod.
• Crabgrass: Broad, light green leaves. Roots at the nodes. Seed head is "fingerlike".
• Russian Thistle: Bushy, round plant. Seedling is succulent. Also called "Tumbleweed". Blows and rolls across the streets to spread seed.
• Kochia: Small fuzzy seedling. Introduced, erect growing 6 feet tall. Multistem, often turning red as matures. Inconspicuous flowers are born upper leaf axils.
• Puncturevine: Prostrate growth habit. Yellow flowers, leaflets are fuzzy to the touch. Seed pod is five nutlets, each with 2 spines/nutlet.
• Prostrate Spotted or Prostrate Spurge: Prostrate growth habit. Off-center leaf attachment. Milky juice in the stem.
• Common Purslane: Succulent, prostrate plant. Round shaped leaves. Self-rooting when cut off or pull up. if left on soil.
• Pigweed, Carelessweed, or Amaranth: Erect plant, often reaching 6 feet in height. Central stem, often turning red at maturity. Terminal seed head is more than twice as long as the lateral seed head. Alternate leaves are lance-shaped.
• Lambsquarters: Erect plant. Leaves have a mealy texture mainly on the underside of leaves, but can be on top. Lower leaves lobed, upper leaves are strap—like.
• Knotweed: Prostrate plant. White papery sheath at leaf axil. Leaves are lance-shaped. Flowers are green-white and born in the leaf axils.
• Common Chickweed: Prostrate growth habit. Leaves are round and entire. Flowers are star-shaped, sepals are green and hairy. Petals are white and deeply lobed, giving appearance of 10 petals but there are only five.
• Speedwells: Prostrate growth habit. Flower is four united white petals. Several different species. Seedpod is heart shaped.
• Annual Bluegrass: Low spreading annual. Narrow, green, boat-tip leaf blades are 3" long. Active growth is in the fall, winter and early spring, when temperatures are cool.

• Musk Thistle: Rosette the first year. Can grow up to 7 feet tall. Solitary flower, pink—purple, on the end of flowering stalks. There are many biennial thistles around, many of these are native and are not related to the musk.
• Mallow: Bushy annual or biennial. Short thick taproot. Leaves are almost circular with 5-7 lobes.

• Simple Perennial: Nonbranching, vegetative structure.
• Dandelion: Yellow, showy flower. Plant is edible. sometimes for making wine.
• Creeping Perennial: Branching vegetative structure which allows the plant to move through the soil.
• Johnsongrass: Erect, with open panicle. Vegetative reproduction is by a rhizome.
• Bermuda grass: Prostrate growth habit. Narrow strap-like leaves. Reproduces by seed, stolons, and rhizomes.
• Nutsedge: Triangle shaped stems. Leaves are three-ranked. Tubers at the end of the rhizome.
• Field Bindweed: Prostrate, vining, creeping. Trumpet-shaped flowers. Deep penetrating roots. Looks like morning glory, but is not an annual like the morning glories.
• Silverleaf Nightshade: Purple flowers with yellow centers. Spines are over plant. Seed born in berries which are green-yellow. Branching root system.
• Creeping Woodsorrel: Prostrate perennial. Creeping stems, 3—8" long. Leaves 3 heart shaped leaflets at tip of long stalks. Leaflets are greenish, purplish, or bronze. Flowers are yellow.
• Black Medic: A low growing annual, biennial, or perennial which reproduces only by seed production. Leaves are divided into 3 leaflets with rounded tips and finely toothed. Central leaflet is on a short stalk.

02/01/2009

From Sunset Magazines web there is an article on a few of the weeds that we commonly find here in the Southwest. Here is the link Click here: Get Good Garden