What to Do About Weeds

Developed by: Susan DonaldsonUniversity of Nevada Cooperative Extension UNCE, Reno, Nev.

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

USDA-ARS

What’s a weed?

Invasive weed spreadWeed Annual Spread Reduced Grazing

Dyers woad 14% 38%

Canada thistle 10% 42%

Dalmation toadflax 8% 46%

Tall whitetop 9% 55%

Leafy spurge 12% 59%

Yellow starthistle 17% 65%

Spotted knapweed 24% 80% UNCE, Reno, Nev.

Weed impacts Decreased grazing

potential Economic losses

from refusals of hay shipments

Decreased crop yields

Cost of controlUNCE, Reno, Nev.

Weed impactsDecreased property values

Loss of wildlife and fish habitat

Impairment of wetland functions

Increased erosionToxicityUNCE, Reno, Nev.

Damaging to the economy or environment Difficult to control Dominate sites

Thre

e D

’s

Dicot (Broadleaf)

•Two true leaves• Broad leaves

have net-like veins

•Coarse tap root

Monocot(Grass)

•One seed leaf•Parallel veins •Fibrous roots

How weeds grow

Monocot Vs Dicot

Plant life cycles Annual

◦ One season for all stages of development

◦ Produce foliage, flower seeds, then die

Yellow starthistleUNCE, Reno, Nev.

Summer annuals◦ Live from spring to fall◦ Examples:

◦ foxtail, pigweed Winter annuals

◦ Germinate in fall and winter

◦ Examples:◦ cheatgrass and

mustard

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

UNCE, Reno, Nev.

Musk thistle

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.

Dandelion

Reproduction Annuals and biennials

◦ Seed ◦ Seed bank

Perennials◦ 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.

Plant parts for broadleaf identification

NRCS, Bozeman, Mont.

Identifying weeds

Have you correctly identified the weed?

Tumble mustard

Spotted knapweed

Dandelion

Yellow starthistle

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

UNCE, Reno, Nev.

How do weeds ensure their success?

They are persistent◦ Will return year

after year

◦ Reproduce vigorously

◦ Spread seeds effectively

UNCE, Reno, Nev.

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.

UNCE, Reno, Nev.

How do weeds spread? Natural means

◦ Wind◦ Water ◦ Animals

Humans◦ Irrigation◦ Roadside shoulder work◦ Construction/ fill dirt◦ Vehicles◦ Tillage◦ Contaminated seed or feed◦ Livestock management

UNCE, Reno, Nev.

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

UC Davis

Hand removal of weeds

Sticky traps and other physical traps/barriers

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

Building a weed management planCONSIDER 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.

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

Minimize soil disturbance and bare ground

Don’t overgraze pastures Apply the appropriate

amount of water Avoid driving in weed-

infested areas

Method 1 of IWM:Prevent the invasion and spread of weeds

USDA NRCS

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

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

Method 3 of IWM: Mechanical Control Cultivation Hoeing Bulldozing Burning Hand pulling Mowing

UNCE, Reno, Nev.

CSUCE

Mulching Solarizing (use clear

plastic for maximum affect)

Repeated tillage can help reduce seed populations UNCE, Reno, Nev.

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

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 weedUNCE, Reno, Nev.

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.

Leaf eating beetle (Diorhabda elongata)

on tamarisk

NDOA

Tamarisk biocontrol

NDOAhttp://www.tamariskcoalition.org/

Method 6 of IWM:Chemical control

UNCE, Reno, Nev.

CSUCE

Manage pastures to minimize weeds

USDA NRCS

Herbicides

Prevention

Proper fertility and species

Dense vegetation, no bare spots

Managed grazing

Naming herbicides Chemical name

◦ N-(phosphonomethyl)glycine Common name

◦ Glyphosate Trade or brand name

◦ RoundUp, Aquamaster, Glypro, Rodeo, etc.

Brand◦ Monsanto

www.scotts.com

Pesticides: an all-inclusive term for all “cides”

Herbicide Fungicide Insecticide

Rodenticide …

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

Effectiveness against target species

Behavior in the environment

Toxicity Safety

Twelve steps to follow before using herbicides:

1. Identify the weeds2. Determine their life cycles3. Consider all control alternatives4. Select the chemical based on

effectiveness, safety, and price5. Read the label carefully and make

sure the herbicide is labeled for the pest and the site

6. Determine the best time to apply the chemical

7. Is the chemical restricted-use-only?8. Consider proximity to water, nearby trees

or shrubs, soil composition, tendency to contaminate water supplies

9. Check the weather 10. Have you read the MSDS?11. Are you applying the appropriate amount

by the best method?12. Do you understand all safety

requirements, and have you followed them carefully? (PPE)

Twelve steps to follow before using herbicides:

Pesticide toxicity

CautionWarningDanger

Less toxic

More toxic

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

Chemical control Selective

◦ Kills only a specific plant or type of plant

◦ Most common types are broadleaf vs. grass USDA NRCS

ALWAYS READ AND FOLLOW THE LABEL DIRECTIONS!

Examples of selective herbicides 2,4-D (Weed-b-Gone, Weedar 64) picloram (Tordon, retricted use, persistent) chlorsulfuron (Telar, Glean) triclopyr (Garlon 3A)

Nonselective herbicides Kills most or all of the vegetation in the

area covered May be pre-mergent or postemergent

chemicals

ALWAYS READ AND FOLLOW THE LABEL DIRECTIONS!

Examples of nonselective herbicides ◦ glyphosate (Roundup)◦ imazapyr (Arsenal; use pre-emergence or

postemergence; has a long residual in high pH soil)

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

UNCE, Reno, Nev.

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

Successful weed management requires constant vigilance and care on the part of the

land manager.

CSUE