Hefner, M., Kratsch, H. 2018, Nevada Nuisance Weeds Field Guide, University of Nevada Cooperative Extension SP-18-02

The plants listed in this field guide are nuisance weeds, those that are troublesome, but have not been listed by the state as noxious weeds.

Similar to noxious weeds, nuisance weeds can spread rapidly and compete aggressively with desirable plants for light, nutrients and water. Many nuisance weeds reproduce profusely, either
by extensive root systems, prolific seed production or both. Many of the seeds produced by these weeds are long-lived in the soil, waiting for the right conditions to germinate and grow.

The impacts of nuisance weeds are similar to those of noxious weeds: increased soil erosion and salinity, increased flood potential, decreased water quality, decreased forage and crop yields, displaced wildlife and native plants, reduced recreational potential, reduced aesthetic value, injury to humans or animals, and increased fire danger.

The purpose of this book is to help homeowners, land managers, green-industry personnel, agricultural producers and recreationists to identify nuisance weeds of Nevada. The over 60 weeds listed in this field guide were selected with input from Extension educators in Nevada counties, other University of Nevada Cooperative Extension personnel and local weed control groups.

Correct identification of a weed is imperative for control. By identifying nuisance weeds early, you can control an infestation while it is small. For larger infestations, correctly identifying the weed will help you implement the control tactics that will successfully manage the weed. For each listed weed, we have included identifying characteristics and several control methods. A glossary is included to define the terms used to describe and identify plant characteristics.

No specific herbicide recommendations are given, as formulations and names change frequently. General herbicide recommendations are provided, such as “broadleaf-selective herbicides,” “grass selective herbicides” or “nonselective herbicides.” Consult your local pesticide dealer for the best product for your weed and site of application. If you choose to apply an herbicide, read, understand and follow all label directions.

We would like to thank all of the people who gave us permission to use their photos in this publication; detailed photo credits can be found on Pages 146-149. We would also like to thank Candy Kiel of The Write Type for graphic design and layout. Special thanks to Ashley Andrews for technical edits.

Funding for this publication was provided by the National Institute of Food and Agriculture (NIFA), Crop Protection and Pest Management, Extension Implementation Program (Grant Number 2014- 70006-22550).

Proper weed identification is a critical step in Integrated Weed Management. Once you have identified the weed, consider all the available control methods for that weed to enhance the long term success of your weed management program.

Weed control methods can be divided into five categories:

#1 Prevention:

Prevention is the first line of defense against weed infestation. Time and money are saved, and landscape degradation can be prevented by keeping weeds from spreading into new areas. Some common prevention measures are:

  • Maintain a healthy, competitive stand of desirable plants that limit the ability of weeds to establish and thrive.
  • Use weed-free hay, straw, seed or mulch.
  • Check containerized plants and sod for weeds before installing them in the landscape.
  • Clean contaminated vehicles and equipment.
  • Educate employees, neighbors, visitors and recreationists about weeds.
  • Prevent movement of soil with weed seeds to uninfested areas.
  • Regularly monitor for weeds to remove infestations when they are small.

#2 Cultural controls:

These strategies rely on proper management practices to make it more difficult for weeds to be successful:

  • Dispose of weed plants and plant parts properly.
  • Do not allow weed plant parts or seeds to escape on the property or to any other property.
  • Mow your lawn at least 3 inches high, and water deeply.
  • Water and fertilize landscape plants appropriately.
  • Manage grazing properly to ensure the health of the pasture. This will limit the ability of weeds to invade the pasture.

#3 Physical or mechanical controls:

These are methods that reduce weed infestations by disrupting the weed growth cycles. They include hand-pulling, tilling, hoeing, mowing, disking and burning. Physical barriers, such as plastic mulch, landscape fabric, organic mulch and rock mulch, can aid in controlling a weed infestation.

#4 Biological controls:

These controls use living organisms to manage pests. Biological controls include insects and grazing animals. While these methods can reduce the spread of a weed infestation, they rarely provide complete control or eradication of a weed infestation.

#5 Chemical controls:

Herbicides are pesticides specifically designed to kill plants. Herbicides can be nonselective; that is, they will kill any plant to which they are applied. There are also selective herbicides. These are subdivided into two groups: broadleaf-selective and grass-selective.

Broadleaf-selective herbicides kill only broadleaf plants and do not damage grass plants. Similarly, grass-selective herbicides kill only grasses and do not harm broadleaf plants.

Weeds are commonly subdivided by their lifecycle. All plants grow through stages: seed to seedling to vegetative growth to flowering and seed production to death. Annual plants complete all growth stages in one growing season, which may be as short as several weeks or as long as six months or more. Biennial plants complete all growth stages in two growing seasons. The first year includes seedling and vegetative stages; the second year includes vegetative, flowering and seed production, and then death. Perennial plants complete all life stages in one growing season (except death). They survive more than two growing seasons and have a seedling stage only during the first growing season. Many live several decades or longer.

Why should you care? Herbicides are most effective when applied to actively growing plants. Growth stage affects herbicide performance, with seedlings being more susceptible to herbicides than mature plants.

Annuals weeds:

Control of annual weeds is most effective when seeds are germinating and when plants are very young. Preemergence herbicides can be used to kill germinating seeds. In unplanted areas, the first crop of weeds may be allowed to germinate, and the young plants are killed with herbicides or tillage. Annual weeds are most resistant to control after flowering, and you risk allowing seed to be produced and distributed, further adding to the seedbank. The seeds of many weeds may remain viable for several years to decades.

Biennial weeds:

In addition to preventing seed germination and controlling young plants, biennials are most susceptible to herbicides at the rosette stage of development, when the plant is sending carbohydrates to the roots for storage. After bolting (production of flowering stems), susceptibility to herbicides drops. Control efforts should focus on prevention of flowering.

Perennial weeds:

Control of perennial weeds involves prevention of seed production, but also control of growth from vegetative reproductive structures (stolons and rhizomes). Stolons and rhizomes have buds that produce new plants. Control is most effective when these weeds are both actively growing and moving sugars to the roots for storage. An effective time to control perennial growth is just before the early flower bud stage, when root reserves have been depleted and sugars from the leaves are beginning to move downward to the roots. Applied herbicides will move with sugars to the roots until the flowers open. Another good time is during the fall, when plants are moving sugars to the roots for storage over winter. Perennial weeds are least susceptible to herbicides at emergence of new shoots or during seed development.

Integrated Weed Management works best when multiple control methods are combined to manage a weed infestation. Weed control plans must also include a revegetation plan. Establishing a healthy, competitive stand of desirable plants is critical to protecting a site from reinfestation.

For the complete user guide with plant list, photos, etc, use the link provided below.

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