1. What to Do About Weeds
Once you’ve learned how grass grows and how to manage grazing, you should notice some improvement in weed infestations. However, some weeds are so competitive and hardy, such as the perennial pepperweed infesting the pasture shown in this slide, that additional management is needed. This lesson will provide you with some of the basic tools of Integrated Pest Management (IPM) and will help you learn a strategy for managing weeds.
Developed by:
Susan Donaldson
University of Nevada Cooperative Extension
UNCE, Reno, Nev.

2. Topics to be covered What is a weed? Why worry about weeds?
How weeds are regulated?
Weed biology
Factors that lead to plant invasion
Preventing invasion and spread of weeds
Identifying weeds
Control - mechanical, cultural, biological, and chemical
Common weeds in your area
Instructor: Weed management tends to be one of the most popular lessons in the Living on the Land series. Note that this is a very long agenda, so determine the most important information for your audience, and adjust accordingly by deleting sections, or schedule a second class. For example, depending upon the preferences of your class, you may decide to shorten the section on pesticide use and safety.
At the second class, you might direct participants to bring in weed samples to identify and develop management strategies.

3. What’s a weed?
For example, leafy spurge is rapidly invading western states and once established, is extremely difficult to control. Leafy spurge, like many invasive weeds, destroys forage and habitat for livestock and wild animals.
The negative impacts from weed infestations are extensive, and often irreversible. Weed infestations reduce or eliminate wildlife habitat, wildlife and livestock forage, and recreational and property values by changing plant communities. Some weeds increase erosion and change the local hydrologic and fire regimes. Other impacts and costs of rapid weed invasion include decreases in crop yields, increased costs of roadside weed control, losses in property value, diminishing water quality, degradation of fisheries, and impairment of recreation areas. Weeds cause a 12 percent overall reduction in crop yields and cost an estimated $24 billion per year in losses. U.S. agriculture alone spends approximately $3 billion per year to control non-indigenous weeds.
USDA-ARS

4. Invasive weed spread
Throughout the western United States, these species are expanding rapidly and affecting our use of the land. Once established, they are often very difficult to control and greatly affect our use of grazing land through decreased productivity and sometimes, toxicity.
Estimates of reduced grazing are species-specific. For example, sheep will graze leafy spurge successfully.
UNCE, Reno, Nev.

5. Weed impacts Decreased grazing potential
Economic losses from refusals of hay shipments
Decreased crop yields
Cost of control
These impacts are usually readily apparent to most small acreage owners. In many states, bordering states will refuse crop or hay shipments that are infested with noxious weeds. This has happened with perennial pepperweed-infested hay from Nevada, for instance.
Instructor: Ask your audience how much they’d be willing to spend, per acre, to control weeds on their property. Hand out the Losses and Damage Caused by Weeds Information Sheet.
UNCE, Reno, Nev.

6. Weed impacts Three D’s Decreased property values
Loss of wildlife and fish habitat
Impairment of wetland functions
Increased erosion
Toxicity
UNCE, Reno, Nev.
These impacts are often less apparent. There are entire ranches infested with noxious weeds, such as spotted knapweed, that have either reduced value or are unsalable. Environmental changes can have a significant cost to local economies if fishermen, hunters, or recreationists are not willing to use weed-infested areas. When tap-rooted perennial weeds invade riparian areas and take over, the soil-stabilizing effects of the native grasses and sedges are lost, and more erosion may occur. A study compared erosion rates between a native grass ecosystem and a monoculture of spotted knapweed, and found that surface water runoff was 56 percent higher and stream sediment yield was 192 percent higher for spotted knapweed dominated sites vs. bunchgrass dominated sites. (Lacey, J.R., C.B. Marlow, and J.R. Lane Influence of spotted knapweed (Centaurea maculosa) on surface water runoff and sediment yield. Weed Technology 3: )
Instructor: This is a good time to introduce or remind participants of the concept of rooting structure (fibrous vs. taprooted). Bring in a piece of sod to demonstrate this principle. Fibrous roots, such as those found in grasses, do a good job of holding soils in place. Ask your participants if they have ever tried to remove the soil from a section of turfgrass. Were they successful? On the other hand, taproots extend deep into the ground, and may be extensive, but lack the fine fibrous root structure needed to stabilize the soil.
Instructor: Later in the presentation, when showing examples of different weeds, be sure to tell which ones are on the noxious weed list, and which are nuisances but don’t fit the “three D’s” of noxious weeds:
Must be DAMAGING
Must be DIFFICULT to control
Must tend to DOMINATE a site
Also review the concepts of good neighboring and community responsibility. Successful weed control requires every landowner to do their part, whether small acreage owners, counties, states, or federal agencies.
Damaging to the economy or environment
Difficult to control
Dominate sites
Three D’s

7. How weeds grow Dicot (Broadleaf) Two true leaves
Broad leaves have net-like veins
Coarse tap root
Monocot
(Grass)
One seed leaf
Parallel veins
Fibrous roots
Weeds differ in their growth habits. Broad-leaved (dicotyledonous) plants have two seed leaves (cotyledons) in each seed. Dicots have broad leaves and may have woody stems. Some species (e.g., sunflower) only become woody in old parts of stems and roots; these are referred to as semi-herbaceous dicots. Most dicot weeds are herbaceous, having little or no woody tissue (e.g., dandelion).
Plants that have a single seed leaf are monocotyledons. Monocots have long, narrow leaves with parallel veins and fibrous root systems. Grasses are members of the plant family Gramineae. Some grasses and other weedy monocots produce underground stems called rhizomes (Kentucky bluegrass, quackgrass) or aboveground runners called stolons (creeping bentgrass), while others produce both (bermudagrass).
It is important to understand the distinction between monocots and dicots. The selectivity of many herbicides is based on which type of plant they kill. Many herbicides kill dicotyledonous weeds in turfgrass. These herbicides do not harm the grass, which is a monocot, but they could not be used in a landscaped planting because the ornamental plants are dicots and would be injured or killed.

8. Grasses (monocots) generally have fibrous root systems that help bind the soil together. If you have ever tried to remove the soil from a section of turf that you have dug up, you’ve observed this personally. Broadleaf weeds (dicots) generally have a tap root. Tap roots do not assist in soil stabilization. When an area becomes infested with tap-rooted weeds, rates of erosion often increase.
Monocot Vs Dicot

9. Plant life cycles Annual Summer annuals Winter annuals
One season for all stages of development
Produce foliage, flower seeds, then die
Summer annuals
Live from spring to fall
Examples:
foxtail, pigweed
Winter annuals
Germinate in fall and winter
cheatgrass and mustard
Knowledge of the life cycle of a particular weed species is important for management. For example, mowing a patch of annual weeds to remove the flowers can prevent seed set. Refrain from cultivating areas where weeds reproduce by rhizomes. Cultivating cuts the rhizomes into pieces and each piece can generate a new weed plant.
Annual weeds complete their life cycle in a single year. If they do not produce seed, they are effectively controlled. However, be aware that if plants have produced seed in the past, that “seed bank” remains in the soil to sprout in future years.
Summer annual weeds grow each spring or summer from seed. Examples include prostrate spurge and ragweed. They mature, produce seeds, and die in one growing season. Seeds generally remain dormant during the winter before germinating the following spring. The majority of annual weeds are of this type. Some annuals, such as crabgrass, can root from leaf-stem junctions, forming dense colonies.
Winter annual weeds (cheatgrass, medusahead, tumble mustard) germinate from seed in the fall to late winter. They mature and produce seed during the following spring, and die in early summer. Seeds of winter annuals remain dormant during the late spring and summer to germinate the following winter.
UNCE, Reno, Nev.
Yellow starthistle

10. Plant life cycles Biennials
Require two seasons for completion of life cycle
First year: develop roots and low-growing leaves
Second year: flowers, sets seed and matures
Examples are mullein and musk thistle
Biennial weeds may germinate at any time during the growing season. Examples include bull thistle and musk thistle. They usually produce a radial cluster (rosette) of leaves lying close to the soil during the first season. In the second year they produce flower stalks (using food stored from the first season's growth), produce seeds, and die. They are easiest to control in the first year by removing the rosettes.
UNCE, Reno, Nev.
Musk thistle

11. Plant life cycles Perennials Live more than two years
Will produce foliage, seed, and reach maturity each year
Examples:
perennial pepperweed
Canada thistle
UNCE, Reno, Nev.
Perennial weeds live for three or more years. Some species may not flower the first year, while others may produce seeds that do not germinate. Many perennials (curly dock, dandelion, and common milkweed) spread primarily by producing seeds, while others (field bindweed, perennial pepperweed, and purple loosestrife) spread both by seed and vegetatively. The latter occurs when attached or broken pieces of rhizomes, stolons, or stem nodes touch the soil and grow new roots.
Perennials are the most difficult weeds to control.
Dandelion

12. Reproduction Annuals and biennials Perennials Seed Seed bank
Simple: Reproduce by seed and pieces of root
dandelions
Bulbous: Produce seed, bulblets and bulbs
wild onion
Creeping: Produce seeds, rhizomes (underground stems), stolons (above ground stems), or creeping roots
pepperweed
UNCE, Reno, Nev.
Remembers that annuals must produce seed to produce new plants. However, if the annuals have reproduced successfully in that location in the past, a substantial “seed bank,” or stored accumulation of seeds, will exist. A great example of this is puncturevine (goathead). It is easy to remove by pulling, but deposits its seeds to sprout in future years, so control must combine removal of this year’s plants before they can set seed with control of sprouting of existing seeds. Some seeds from perennial plants may stay viable for many years. Spotted knapweed seeds, for example, will still sprout as long as 20 years after they have been produced.
Because perennials reproduce not only by seed but also by roots, control must remove or kill the root of the plant. Be aware that digging may leave parts of root fragments in the soil, which may then produce new plants.

13. Plant parts for broadleaf identification
Identifying
weeds
Plant parts for broadleaf identification
Learning the names of some of the plant parts will help you use descriptions or keys. The following are just a few of the applicable terms as shown in the diagram. The cotyledon is the seed leaf. Broadleaf plants produce two cotyledons. The petiole is the leaf stalk that bears the leaf. Leaves are described by shape, pattern of venation (midvein, the central vein; palmate, or divided from a common point, like fingers on a hand; or pinnate, arranged on either side of a central vein) , type of margin (entire, not toothed, notched, or divided; toothed, with small lobes or points along the margin), etc. The terminal bud is the bud at the tip of the stem that will develop into a shoot or flower. Leaves are arranged on stems in two main patterns: alternate or opposite. Alternate leaves are borne singly at each node, while opposite leaves are borne across from each other at the same node.
NRCS, Bozeman, Mont.

14. Have you correctly identified the weed?
Spotted knapweed
Tumble mustard
Dandelion
Seedlings are often the most difficult to identify. It is very easy to make mistakes in identifying juvenile plants, so be sure to seek assistance.
Instructors: Ask your students to identify each weed. Chances are, they will only be able to identify the dandelion photo on the next slide.
Bottom: tumble mustard
Left: spotted knapweed
Right: perennial sowthistle
Yellow starthistle

15. How do weeds ensure their success?
They are very competitive
Grow well in spite of interference from other plants
They take advantage of the characteristics of sites, including:
Exposed or disturbed soil (grading road shoulders)
Turfgrass, range, pasture or groundcover that is weakened by disease, pests, or poor management
Places where a desired species is not well-adapted to its environment
Weeds are well-adapted to growing in disturbed sites, and are often the first plants to show up when lots have been bladed. They will move into sites where the vegetation has been weakened by poor management, or where the species present are not well adapted to the local soils or precipitation.
Weeds always seem to be more competitive than the desired plants! Invasive weeds will move into even healthy stands of plants and quickly displace them, forming a monoculture (solid stand of a single species). In this photo, purple loosestrife is invading a wetland area that is inhabited by dense wetland species.
UNCE, Reno, Nev.

16. How do weeds ensure their success?
They are persistent
Will return year after year
Reproduce vigorously
Spread seeds effectively
Weeds are supremely effective at reproducing and persisting, which is what makes them problems in the first place! These Canada thistle seeds will float long distances with the wind, and the original plants will also reproduce by sending out shoots to form new plants.
Instructor: Have your students name some of the ways in which seeds are spread effectively (floating on the wind, like thistles; sticking onto animals’ coats or your socks, such as cocklebur or puncturevine.)
UNCE, Reno, Nev.

17. How do weeds ensure their success?
They are harmful
Can alter the site they grow in by
accumulating salts,
changing water table depths,
increasing erosion,
increasing wildfire frequency,
Etc.
Cheatgrass is a well-known example of an invasive plant that burns readily, increasing wildfire frequencies. Tamarisk is another example of a weed that changes a site in two ways. First, it lowers the elevation of the water table, making it impossible for riparian plants to survive. Second, it extracts salts from within the soil profile, moving those salts through the plants to the leaves, and then depositing the salt-laden leaves on the soil surface. This increases soil salt levels so other plants can neither germinate nor grow.
UNCE, Reno, Nev.

18. How do weeds spread? Natural means Humans Wind Water Animals
UNCE, Reno, Nev.
Natural means
Wind
Water
Animals
Humans
Irrigation
Roadside shoulder work
Construction/ fill dirt
Vehicles
Tillage
Contaminated seed or feed
Livestock management
Nature has provided several means by which weed seeds spread. Downy-type seeds float in the wind and are carried over great distances. Other seeds may fall into streams or rivers and are carried downstream with flowing water. Animals may move seeds by consuming and then excreting them with their manure, or by dropping off seeds that have stuck to their coats or feathers.
Surface irrigation water has been shown to carry many kinds of weed seed into cropland. A study conducted in western Nebraska showed that surface irrigation water could contain up to 77 different kinds of weed seeds and deposit nine seeds per square yard, or approximately 38,000 seeds per acre during an irrigation season.
Many weed seeds pass through the digestive tracts of animals and remain viable. Some require this treatment in order to sprout. Spreading untreated manure to fertilize cropland or pastures systematically introduces weed seeds across fields.
Sometimes contaminated crop seed is the source of new weed species, as is farm equipment or road repair equipment that picks up seed from a contaminated field or roadside. Fill dirt and gravel are other common sources of weed infestations.

19. What can we do? Practice Integrated Pest Management (IPM)
IPM is a sustainable approach to managing pests that combines biological, cultural, physical and chemical tools in a way that minimizes economic, health, and environmental risks
It’s clear that weeds have many adaptations that allow them to become troublesome in the environment. The solution is not simple, and requires a focus on the many tools available to us.
Integrated Pest Management provides a framework for the effective management of all pests, including weeds. The definition of IPM from the National IPM Network: “Integrated pest management (IPM) is an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties. Pesticides are used only after monitoring indicates they are needed according to established guidelines, and treatments are made with the goal of removing only the target organism. Pest control materials are selected and applied in a manner that minimizes risks to human health, beneficial and nontarget organisms, and the environment.”

20. Sticky traps and other physical traps/barriers
Hand removal of weeds
UC Davis
Integrated pest management (IPM) is an approach that first assesses the pest problem (is damage due to a pest, or something else?), evaluates the appropriateness and effectiveness of various pest management options, and then implements a system of management actions within a defined area. The goal of IPM is to reduce pest damage while protecting human health, the environment and economic viability. IPM adapts to the situation and goals and values of the manager as well as public and private values.
Sticky traps and other physical traps/barriers

21. Components of an IPM program
Planning
Setting action thresholds
Monitoring and detection
Identification
Implementation
Evaluation
IPM tools for weed management (IWM)
Prevention
Eradication
Mechanical controls
Cultural controls
Biological controls
Chemical controls
The steps of an IPM program include the following:
Planning: A proactive approach of anticipating problems takes people out of the reactive mode and allows them to take advantage of all available management options.
Setting action thresholds: Values, priorities, economics, health issues, and environmental impacts all determine when intervention will occur.
Monitoring and detection: Ongoing monitoring and timely detection to minimize loss and/or safeguard human health and the environment are critical.
Proper identification: The cause of the problem must be correctly identified.
Action and implementation: Actions depend upon the pest problem, site situation, and the available management options.
Evaluation of results: Regular monitoring will allow you to determine if your IPM strategy was successful, or whether it can be improved.
Adapted from:
The specialized application of IPM to weed management is termed “Integrated Weed Management,” or IWM.
The key to weed management is to create a favorable environment for growth of desirable plants. Plant competition is a good tool that is often overlooked and should be used first, but not exclusively. The IPM toolbox includes prevention and mechanical, cultural, biological and chemical controls, as we will describe. Effective weed management depends on the appropriate application of a combination of these tools.
All control methods have limitations. There are a number of factors to be considered when selecting an appropriate control method. Minimizing the spread of existing weeds and preventing the growth of new weeds should be the focus of a weed management program. One weed plant can produce hundreds of seeds that can disperse over a wide area.

22. Building a weed management plan
CONSIDER THE:
Identity of the weed
Biology of the weed
Extent of the problem
Environmental conditions of the site
Ultimate objectives for the site
Most economical solution
UNCE, Reno, Nev.
The elements of a weed control plan include the elements of IPM. Start by identifying existing weeds that are causing problems, as well as other weeds that are likely to invade and cause problems in the future. Then, make sure the weed has been correctly identified, and consider its life cycle (annual/biennial/perennial) and method of spread (seeds vs. roots). For instance, there is no point in applying a preemergent herbicide for control of the annual weed, puncturevine, if there is no puncturevine! It would also be fruitless to apply a preemergent herbicide that acts by preventing weed seed germination to control established perennial weeds.
For weeds that may invade or spread if not prevented from doing so, identify the vectors to control. Vectors such as seed, hay, manure, straw mulch, equipment, vehicles, camping gear, or clothes, that can be managed to prevent weed infestation, must be monitored continually and vigilantly. Consider soil types, climatic conditions, and water availability, and assess existing desirable vegetation. For example, large areas of well-established invasion are more difficult to control than smaller invasions. A permanent pasture is not suited to repeated tilling, but frequent mowing may be acceptable and will disrupt seed production to help control annual weeds.
While hand-pulling of weeds is often a very effective method of control, its feasibility is limited by high labor costs in large infestations.
Are there any environmental or health risks of a given control method? Are there physical, legal, or political limits?

23. Method 1 of IWM: Prevent the invasion and spread of weeds
Plant clean, weed-free seed
Avoid spreading weed seeds with manure
Sanitize tillage and harvest equipment prior to moving them from one field to another
Plant and maintain desirable plant species
Consider crop rotation to slow weed spread
Prevention, or never getting a problem weed, is the most cost-effective method of control. It is very easy to introduce weeds via contaminated feed, equipment, or manure. Similarly, spreading uncomposted manure spreads weed seeds also. Most people don’t know that weed seeds can be passed through the digestive tract of livestock for as long as seven days after consumption, and will often be viable. If your livestock graze exclusively on your own pastures, you will only spread existing weed species. If, however, you feed weedy hay, you run the risk of introducing many other weeds. Again, if you spread uncomposted manure from outside animals, you run the risk of introducing new weeds on your property.
Another problem is the intentional planting of species that are not suited to the local climate and soils. For example, when easterners move west, they often want to mimic a familar landscape style, despite the difference in precipitation rates, etc. Resist the temptation! Plant species that are known to do well in your area.
The last method is crop rotation. If you continually plant the same crop in a field, you are selecting for weeds that like the growing conditions that crop provides. If you change the crop, you change the growing conditions and make the area inhospitable to that particular weed. For example, if you continually grow alfalfa in a field, you will select for weeds that like nitrogen (alfalfa is a legume and “fixes” nitrogen in the soil) and very little shade. If you rotate corn in that same field, you now have planted a crop that needs nitrogen and provides shade; these would be inhospitable conditions for those same weed species. It does not mean you will not have weeds growing in the corn field, it just means they will be different weed species.

24. Method 1 of IWM: Prevent the invasion and spread of weeds
Minimize soil disturbance and bare ground
Don’t overgraze pastures
Apply the appropriate amount of water
Avoid driving in weed- infested areas
If bare ground exists, you can be sure that weeds will invade, so a decision to maintain an area of bare ground is also a decision to continually struggle with weeds.
Overgrazing leads to weed invasion because it stresses plants, depletes root reserves, and leaves openings for weeds to grow. Remember how grass grows and how important it is to leave enough blade height when grazing. A healthy plant community is the best defense against weeds.
How can you tell that a pasture has been overwatered? Examine the type of plants growing in the pasture. Invasion by wiregrass, or rushes (Juncus spp.), is a telltale sign. A stand of wiregrass is easily seen in a pasture because of its bluegreen color. Rushes are low in forage value and bring yields down. They are a sign of overwatering.
After driving through a patch of weeds, seeds and plant parts can drop off slowly for 10 or more miles down the road. Tires on all vehicles, including RVs, carry weed seeds over long distances. Ideally, contaminated vehicles will be high-pressure spray washed before leaving weedy areas. Alternatively, just don’t drive through patches of weeds.
USDA NRCS

25. Method 1 of IWM: Prevent the invasion and spread of weeds
Don’t transport flowering plants that you cannot identify
Pull small patches before seed is formed
Carefully remove weeds that have flowered
Report new infestations
You can do your part to prevent the spread of weeds by fighting the urge to transport or transplant seemingly “pretty” weeds that then become big problems. If you find small patches of invasive weeds, be sure to report the location and species to the appropriate authority.

26. Method 2 of IWM: Eradication
Removal of all weeds of a given species from an area so they will not recur unless reintroduced
Must deplete seed bank of viable weed seeds by controlling all seedlings
Only feasible for small, new invasions
Must revegetate the area
The word “eradication” is often misused and confused with control. If weeds have been present in past years, remember that their seeds will be present in the soil, and eradication is probably not feasible, or will surely require repeated action over many years. The best time to control weeds is in the first growing season, when they are all “annuals.” Constant and careful monitoring is key to controlling weeds.

27. Method 3 of IWM: Mechanical Control
Cultivation
Hoeing
Bulldozing
Burning
Hand pulling
Mowing
UNCE, Reno, Nev.
Mulching
Solarizing (use clear plastic for maximum affect)
Repeated tillage can help reduce seed populations
Mechanical control methods physically disrupt weed growth. They are the oldest and most common methods used worldwide, and are especially appropriate for controlling annuals as long as you apply the method in time to prevent seeds from being produced. Mechanical means include:
Cultivation or hoeing: Causes soil disturbance and may increase erosion; avoid broad-scale application in riparian areas.
Bulldozing: Increases soil compaction, may have effects on animals and other vegetation, and may increase future weed infestations and soil erosion.
Burning: Used prior to herbicide application where dead material may prevent good contact. Avoid damaging non-target vegetation. Burning will affect air quality, has potential for causing or preventing catastrophic wildfire, and impacts animals, insects, microorganisms and native plants. The overall impact can be quite positive on native species.
Hand pulling: Useful for small-scale infestations; labor intensive. Be aware of potential toxicity from the weed and wear gloves when pulling. May take 10 or more years to deplete root and/or seed reserves of well-established perennial plants.
Mowing or cutting: Reduces seed production; appropriate timing is essential. Mowing can adversely affect insect populations, including biocontrol agents.
Mulching: Barriers and mulches often eliminate access to soil in which weed seeds can germinate. With some weeds, mulching prevents their germination. With others, the few weeds that emerge are easy to pull. While this is often a good, long-term solution to a weed problem, it is usually expensive to install. However, eliminating the need for other weed management may pay for the installation of the barrier over the long term. Most effective with annual weeds.
Solarizing: Clear plastic sheeting placed over the ground in direct sunlight may cook weeds and other vegetation in the hothouse conditions created underneath the plastic.
Tillage: This method is usually limited to croplands. Be careful, as tillage may spread some perennial weeds, such as perennial pepperweed, that sprout from cut rhizomes. Tillage affects soil structure, and erosion by wind and water may bring weed seeds to the soil surface. Repeated cycles of tillage and germination may help reduce annual weeds, and may be especially useful for organic gardeners who wish to avoid the use of herbicides.
CSUCE
UNCE, Reno, Nev.

28. Method 4 of IWM: Cultural control
Cultural control involves using land management tools that make it difficult for weeds to be successful
Shading
Water and nutrient management
Correct seeding rates
Cultural control includes practices that encourage desirable plant growth. Fertilization, irrigation, and planting appropriate species at optimum densities are practices that help desirable plants out-compete weeds. Common cultural methods include:
Shading: The establishment of competitive vegetation may “shade out” weeds. For example, purple loosestrife will not grow well if shaded 50 percent or more of the day.
Water and nutrient management: Optimal water and fertilizer application for the plants you wish to grow can give those plants a fighting chance.
Flooding: This method requires a water source that can be regulated. Avoid spreading weed seeds with flowing water.
Planting appropriate competitive native or even non-native species.
Good seedbed preparation.
Destruction of weed competition before planting.
Correct seeding rates and dates.

29. Method 5 of IWM: Biological control
Biological control is the use of one organism to suppress another
Can reduce pesticide use
Agents can be free or purchased
Can effectively and economically suppress pests
Does not eradicate a weed
Biological control is the intentional use of living organisms to reduce (NOT eradicate!) the population of a pest. Biological control may include the use of insects, nematodes, mites, plant pathogens, and vertebrates, such as grazing animals. Often more than one biocontrol agent is introduced to help control a weed, and each agent affects the weed in a different way. Successful biological control depends upon the identification of appropriate organisms, introduction and adaptation to the environment, including completion of the life cycle, and a sufficient quantity of plant material to support a population of the biological control agent. This method may provide a useful tool in organic gardens.
Biological control of weeds in rangelands and waterways is being extensively investigated and seems to have great potential for some weeds. It is sometimes more economical than chemical controls, and usually prevents economic damage to neighboring vegetation, since biological control agents are required to be very specific for a particular pest before they are allowed to be introduced. It is the most selective and sustainable means of weed control, and can provide a long-term answer to some weed problems.
Careful management of grazing animals to decrease weed populations can be considered biocontrol. Because livestock select their grazing areas in a pasture, the species of plants, and the plant parts, this tool requires knowledge and monitoring. Through trial and error, certain livestock can effectively manage some weeds. Realize that palatability and preference are always relative to what’s offered, so pick the appropriate time for control. Feed livestock weed-free products and keep them off weed-free areas for at least five days after grazing on weed-infested fields, or the weed seeds will be spread in manure.
UNCE, Reno, Nev.

30. Method 5 of IWM: Biological control
Characteristics of successful biocontrol agents:
Prolific
Thrive and become widespread in all habitats and climates that the pest weed occupies.
Good colonizers of new areas.
NDOA
Leaf eating beetle (Diorhabda elongata) on tamarisk
In order for biocontrol agents to be successful, they must be able to effectively damage the target weed and decrease the population of the weed. At the same time, they must set up housekeeping, produce a sustainable population, and move into new populations of the weed. Biocontrol agents have been used on musk thistle, yellow starthistle, puncturevine, purple loosestrife, tamarisk, and other problem weeds. However, the same biocontrol agent may not be successful when moved to other locations with different climates and site-specific factors.
Also, biocontrol is a slow process. You may not see results for six to 10 years after introduction, as populations of the weeds are slowly reduced.

31. Tamarisk biocontrol http://www.tamariskcoalition.org/
Both larvae and adults of the biocontrol agent, Diorhabda elongata, eat the leaves of tamarisk trees. The beetle is prolific, reproduces readily, and as one tree is defoliated, the insects move to another. After several years of defoliation, it appears that the trees begin to die.
NDOA

32. Method 6 of IWM: Chemical control
Chemical control is often the method of choice for many homeowners. They go to their local garden or hardware store, pick a product off the shelf, go home, mix it up at twice the suggested concentration (after all, that’ll make it work better, won’t it?) and apply it incorrectly. If results are not immediate, another application is often made. The results? Poor weed control and a much greater chance of water contamination and health risks. Learn to select the appropriate control based on the plant identification, life cycle, integrated weed management, and future objectives for the site. The homeowner who applies a preemergent herbicide and then attempts to sow a wildflower bed will be very unhappy!
Prior to using chemical controls, make sure you’re aware of pesticide safety, and check whether permitting or certification is required. Some chemicals are not registered for use in all states. Others are “restricted use” chemicals and may only be applied by certified personnel. Be safe, not sorry!
UNCE, Reno, Nev.
CSUCE

33. Manage pastures to minimize weeds
USDA NRCS
Herbicides
Prevention
Proper fertility and species
Dense vegetation, no bare spots
Managed grazing
You’ve already learned to manage grazing to keep plants healthy and vigorous. Good pasture management will help reduce weed problems, and your reliance on herbicides will be minimized.

34. Pesticides: an all-inclusive term for all “cides”
Herbicide
Rodenticide
Fungicide …
Insecticide
Naming herbicides
Chemical name
N-(phosphonomethyl)glycine
Common name
Glyphosate
Trade or brand name
RoundUp, Aquamaster, Glypro, Rodeo, etc.
Brand
Monsanto
The word “pesticide” is often misused. It is a general term for substances that kill pests. There are many types of pesticides. The type that is used to kill plants is called an herbicide.
Herbicide names can be very confusing. First, there is the chemical name, or the name that chemists have assigned to the herbicide to describe the chemical structure. For example, from the chemical name for Roundup, it is clear that the structure includes the amino acid, glycine. Chemical names are long and difficult to pronounce, however, so common names for the active ingredient are used. In the case of Roundup, the common name for the active ingredient is glyphosate, pronounced gly – foh – sate (NOT gly – fos – fate!).
Each manufacturer will then assign a trade name to their product, which is the name for the formulated product, NOT the active ingredient. Roundup is one of the most recognized trade names in the business. Marketing efforts focus on promoting brand recognition for the trade name. The brand itself refers to the manufacturer, in this case, Monsanto.

35. To spray or not to spray? Consider:
The goals for the site
The site conditions
Accessibility
Proximity to surface water
Depth to groundwater
Presence of rare species
Toxicity
Safety
Effectiveness against target species
Behavior in the environment
Before you can make the decision to apply an herbicide, there are many factors to consider.
First, consider your goals for the site. Will it eventually become an organic vegetable garden? Is the area used by children and animals, and you’d prefer to avoid the use of chemicals? Or maybe the site is meant to be kept free from all plants, such as a bare road shoulder in an arid region. These are very different situations that require different solutions.
Then, consider any special characteristics of the site. Can you access the site by car or foot, or is it in difficult terrain? Are there concerns about contaminating water, or harming rare or endangered species?
When selecting an herbicide for use against a weed it is essential to identify the weed species, since many herbicides kill only specific weeds (e.g., only grasses prior to germination, only broadleaf plants). Some herbicides are nonselective and will kill all vegetation whose leaves they contact. For example, Roundup, which contains the chemical ingredient glyphosate, will kill all susceptible vegetation. Other herbicides such as 2,4-D are selective but may be absorbed by the roots of adjacent plants and may injure or kill them unintentionally. These products are slowly absorbed, and effects may not be visible for a week or more.
To determine which herbicides are in a product, look at the active ingredients listed on the label. The rest of the label will provide a list of approved target weeds and application precautions. Also consider that use of a nonselective herbicide for weed control may lead to an increase in weed problems in the future. The bare ground created following their use could serve as a site for invasion by new weed species.

36. Twelve steps to follow before using herbicides:
Identify the weeds
Determine their life cycles
Consider all control alternatives
Select the chemical based on effectiveness, safety, and price
Read the label carefully and make sure the herbicide is labeled for the pest and the site
Determine the best time to apply the chemical
When selecting an herbicide for use in controlling a weed it is essential to identify the weed species, since many herbicides kill only specific weeds (e.g., only grasses prior to germination, only broadleaf plants). Once you know the identity of the weed, you can determine how it reproduces, and which methods of control are appropriate. For example, mechanical methods can be effective in the control of annuals and biennials, while perennial weeds that spread from root fragments may require chemical control methods.
Next, look at the characteristics of the herbicide. How harmful is it to humans and other organisms? How well does it work, and can you afford the cost?
Read the label to be aware of important requirements when using herbicides, such as licensing and training. Environmental concerns make it essential to follow all label and site directions. The label is the law, and as such, it is your responsibility to make sure to carefully follow all precautions. Herbicide injury to desirable plants is a common side effect of herbicide application by untrained individuals who allow spray and vapor drift inappropriately when applying the product. Risk of spray drift increases with increasing wind, higher temperatures, lower humidity, certain nozzle types, etc. Whenever possible, spray early in the morning, or consider the use of rope wicks or wipe applicators. Common symptoms of herbicide injury include plant or leaf yellowing and/or bleaching, root stunting, distorted growth, and death.
Timing is also important. Most often, you’ll apply herbicides to green, actively growing plants, although there are some exceptions.

37. Twelve steps to follow before using herbicides:
Is the chemical restricted-use-only?
Consider proximity to water, nearby trees or shrubs, soil composition, tendency to contaminate water supplies
Check the weather
Have you read the MSDS?
Are you applying the appropriate amount by the best method?
Do you understand all safety requirements, and have you followed them carefully? (PPE)
Restricted-use herbicides can only be sold to certified applicators who have completed training and passed an applicator exam. These products are clearly marked on the label.
Increased contamination of surface and groundwater supplies can result from improper use of chemicals. Risks are greatest in areas with shallow water tables. Mix chemicals and clean containers in areas away from water bodies and wellheads, preferably on impervious surfaces.
Be aware of the weather, and avoid spraying when rain is imminent, or the product will be washed off the weeds, increasing chances of contamination. Don’t spray on windy days, when drift can damage other plants. Many products have a minimum and maximum temperature range for their use; be sure to follow these directions also.
An MSDS is a material safety data sheet. Each product has one. Ask for it when you purchase an herbicide, and read it carefully. MSDSs are also available on the Internet.
It is imperative to apply the appropriate amount of herbicide. Too little will not provide control, and may act as a growth accelerator (such as 2,4-D). Too much may burn the top of the plant before the product can be transported to the roots, and perennials will readily regrow. Rates are provided on the label.
Finally, protect yourself by using the appropriate personal protective equipment (PPE). Protect your eyes with goggles, and wear chemical-resistant gloves. A cap with a visor will help keep spray out of your face.
Instructor: Distribute Pesticide Safety Checklist Information Sheet

38. Pesticide toxicity Caution Warning Danger Less toxic More toxic
The U.S. Environmental Protection Agency (EPA) has developed a set of signal words that are placed on labels and containers to allow you to access danger from an individual product.
Caution is used for herbicides with relatively low toxicity or corrosiveness. It takes more than 1 ounce in a single dose of the concentrated chemical to kill the “average” adult.
Warning indicates a moderately toxic or corrosive pesticide. On average, it takes 1 teaspoon to 1 ounce of the chemical in concentrated form, taken through the mouth, to kill an adult. Severe injury may occur at lower doses.
Danger indicates a highly toxic pesticide. It may take a few drops to one teaspoon of the chemical in concentrated form, taken through the mouth, to kill an adult. Severe injury may occur at even lower doses.

39. How do herbicides work?
Interfere with or disrupt biochemical or physiological processes in susceptible plants
Often affect a specific enzyme or reaction
Example: amino acid inhibitors - glyphosate
To be effective, herbicides must come into contact with the target weeds, be absorbed, move to the site of action, and reach sufficient levels in the plant that it is affected. The term “mode of action” refers to this sequence of events that results in plant death. Understanding the mode of action can be helpful in knowing which groupings of weeds will be susceptible, diagnosing herbicide injury problems, and preventing the development of herbicide-resistant weeds.
Herbicides are often grouped by their mode of action. Some of the more common modes of action include:
Plant growth regulators (2,4-D, MCPA)
Amino acid biosynthesis inhibitors (imazapyr, chlorsulfuron, glyphosate)
Fatty acid biosynthesis inhibitors (fluazifop)
Seedling growth inhibitors (pronamid, dichlobenil, preemergents)

40. ALWAYS READ AND FOLLOW THE
Chemical control
Selective
Kills only a specific plant or type of plant
Most common types are broadleaf vs. grass
USDA NRCS
Examples of selective herbicides
2,4-D (Weed-b-Gone, Weedar 64)
picloram (Tordon, retricted use, persistent)
chlorsulfuron (Telar, Glean)
triclopyr (Garlon 3A)
Selective herbicides are used when you want to spare certain plants. For example, 2,4-D can be used to kill broadleaf weeds in turfgrass, without harming the nearby grasses. Selective herbicides are also used when bare ground is not desired.
Other selective herbicides, such as fluazifop (Fusilade), kill only grasses and spare broadleaf plants. These products can be useful in agricultural settings or landscape beds.
As with all pesticides, make sure the herbicide you choose is compatible with your land use. If you are using a herbicide in a pasture, hay field, or cropland, be sure that herbicide is labeled for that land use. Note the withdrawal period for grazing animals or harvesting crops and plan accordingly.
Instructor: Customize the presentation by adding chemicals that are commonly used in your area, or by removing those that are not registered for use in your state.
ALWAYS READ AND FOLLOW THE
LABEL DIRECTIONS!

41. Nonselective herbicides
Kills most or all of the vegetation in the area covered
May be pre-mergent or postemergent chemicals
Examples of nonselective herbicides
glyphosate (Roundup)
imazapyr (Arsenal; use pre-emergence or postemergence; has a long residual in high pH soil)
Nonselective herbicides will leave patches of bare ground, which are invitations to weed invasion. Carefully consider whether your interests are best served by using nonselective herbicides over a large area, or by using them on a spot basis to control individual weeds.
If you are attempting to kill existing vegetation prior to renovation, then a nonselective herbicide such as Roundup may be the best choice.
Instructor: Distribute Reading Pesticide Labels Activity Sheets and sample labels. Have students find the environmental warnings and complete the worksheets. You may customize the exercise to commonly used pesticides in your area. Labels may be downloaded at:
ALWAYS READ AND FOLLOW THE LABEL DIRECTIONS!

42. Weed treatment in riparian areas
Select the most effective treatment methods for the site
If herbicides are used, be sure the label allows application adjacent to or in the water
Consider wipe application to minimize spray drift
In many parts of the United States, surface and groundwater supplies have been contaminated with herbicides. When no other alternatives for weed control exist, it may be necessary to use herbicides in or adjacent to waterbodies. If invasive weeds are allowed to proliferate, water quality and habitat are often degraded.
It is essential to read the label to ensure that the product you have selected is labeled for use in these situations. For example, the water-labeled formulation of glyphosate (Roundup) is called Rodeo These products have been tested for safety of use. Whenever possible, spray away from the water surface, or use a wipe applicator as shown in the photo to avoid spray drift. A wipe applicator consists of a hollow tube with a paint roller-type device at the end. The chemical is poured into the tube, the tube is capped, and the chemical is applied by wiping onto individual plants.
UNCE, Reno, Nev.

43. Now what?
Go home and inventory and identify the weeds on your property
Why do you have a weed problem? What can you change about the way you manage your property to decrease weeds?
Determine the most appropriate controls for the site
Make weed management plan
Start working!
Monitor your property for weeds on a continual basis
Instructor: Below is the homework assignment. Hand out:
Weed Management Plan Checklist Information Sheet
Ten Steps to Effective Weed Control Information Sheet
Weed Management Plan Activity Sheet
Make sure students understand their tasks and their resources for help. They should bring their completed weed plan activity sheet to the next class.
Remind students that productive forage is their best defense against weeds and should be their primary goal.

44. Successful weed management requires constant vigilance and care on the part of the land manager.
In weed management, your job is never done, but constant monitoring and early action will make the job a lot easier.
Photo shows a field bindweed infestation in Colorado, courtesy of Colorado State University Cooperative Extension.
CSUE