R A L P H W H I T E S I D E S

U TA H S TAT E U N I V E R S I T Y

P R O F E S S O R A N D

E X T E N S I O N W E E D S P E C I A L I S T ( E M E R I T U S )

What Do Weeds Think?

What is a Weed?

Plant out of place

Any plant growing where it is not desired

Any plant someone will pay to remove or kill

Any plant other than the crop/plant sown

Plants that are competitive, persistent, and

pernicious. They interfere with human activities

and, as a result, are undesirable. (Ross & Lembi)

Common Approach

What is that plant?

How do I kill it?

Thoughtful Approach

What is that plant?

Why is it there?

Why is it there now?

How do I keep it from being there in the future?

Life Cycles and Plant Families

“ACEAE”

Annual

Winter annual

Summer annual

Biennial

Perennial

Simple perennial

Creeping perennial

Plant Families

Asteraceae (sunflower)

Zygophyllaceae (caltrop)

Convolvulaceae (morninglory)

Brassicaceae (mustard)

Poaceae (grass)

Specimen Weeds

Common dandelion

Puncturevine

Field bindweed

Quackgrass

Crabgrass

Shepherd’s purse

Dyer’s woad

Herbicide Nomenclature

Pre-emergence

Post-emergence

Contact

Systemic (translocated)

Cultural Control/Mechanical Control

Competition

Tillage

Fertilizer

Irrigation

Management Strategies

Annuals

Biennials

Perennials

Management Strategy for Annuals

Annuals on the list for today

Crabgrass

Puncturevine

Shepherd’s purse

Management Strategy for Crabgrass

Digitaria sanguinalis

Poaceae – native to USA, Caribbean

Summer Annual = germinate 55 F

Single Large plant = 150,000 seeds –

seed survive up to 15 years

Objective = prevent seeds

Forsythia in bloom

Large Crabgrass

Large Crabgrass

Mower Damage to Turf

Pre-emergence Herbicide Failure

Management Strategy for Puncturevine

Tribulus terrestris

Caltrop Family

Summer Annual – native to Mediterranean Region

One large plant in California produced 576,000 fruits.

Assuming 2 seeds per segment = 1,152,000 seeds/plant

Germinates all season – lives in soil at least 4 years

Susceptible to glyphosate, 2,4-D, dicamba

Mechanical control = sweep seeds, vacuum seeds, roll

old pumpkins, or carpet

Puncturevine

Military Caltrops

Puncturevine Caltrops

Mechanical Control of Puncturevine

Shepherd’s Purse Management

Capsella bursa-pastoris

Winter annual mustard

Member of mustard family

Native of Europe

Single plant produces several thousand seeds

Remain viable for many years

Seeds remain dormant in the dark - mulch

Shepherd’s Purse Flower

Shepherd’s Purse Seed Pods and Rosette

Management Strategy for Biennials

Biennial on the list for today

Dyer’s Woad

Dyer’s Woad

Isatis tinctoria

Native to Central and Western Asia

Winter annual, biennial, or short-lived

perennial

Plants produce 350-500 seeds

Seed longevity under field conditions

unknown – some evidence for 8-10 years

Dyer’s Woad in Flower

Dyer’s Woad Seeds

Management Strategy for Perennials

Perennials on the list for today

Common dandelion – simple

Field Bindweed – creeping

Quackgrass – creeping

Common Dandelion

Taraxacum officinale

Native to Eurasia

Simple perennial with fleshy taproot

Spread by seed and new shoots from

roots

Dent-de-lion

Common Dandelion Inflorescence

Dent-de-lion

Simple Perennial

Lilac Bush

Lilac Bush

Field Bindweed

Convolvulus arvensis

Creeping Perennial

Native of Europe, North Africa,

Asia

Reproduces by seed and roots

Seed longevity > 50 years

Field Bindweed Seed

Field Bindweed Flowers

Field Bindweed Roots

Quackgrass

Agropyron repens (Elymus repens)

Creeping perennial

Native to Europe and Western Asia

Reproduces by seed and rootstock

(rhizomes and roots)

Seed longevity 2-4 years

Quackgrass Seed and Leaves

Quackgrass Rootstock

What are Annuals Thinking?

Seed production

Not necessary to develop huge root

reserve, plan to die after they

produce seed anyway

Seed dispersal

What are Biennials Thinking?

Rosettes

Vernalization

Seed Production

Short-lived perennial

What are Perennials Thinking?

OK to produce seed, but not necessary

Establish significant root reserves

Develop brittleness as an ecological

advantage

Send progeny elsewhere and rebuild

root reserve

Field Bindweed Roots

Brittleness

Saltcedar (tamarisk)

Salt Cedar on the Freeway

Salt Cedar on the Freeway

Salt cedar

What Should Humans be Thinking About Weeds?

Stop annuals & biennials from seeding

Recognize apical dominance in

perennials

Understand “Source to Sink” in

perennials

When using herbicides understand

“selective” vs “non-selective”

Apical Dominance

Herbicide Selectivity

Herbicide Selectivity

Herbicide Selectivity

Herbicide Selectivity

Source to Sink Translocation

Selective Grass Control in the Landscape

Selective Grass Control in the Landscape

Selective Grass Control in the Landscape

Selective Grass Control in the Landscape

Sethoxydim – Poast, Segment, others

Fluazifop – Fusilade II

Clethodim – Clethodim 2EC

Lawn Violet

Lawn Violet

Vinca major – Big Periwinkle

Lawn Violet (Viola sororia) and Vinca

Triclopyr – Garlon 3A (violets are

on the label)

Carfentrazone – Quicksilver

Triclopyr + clopyralid – Confront

Pillars of Weed Management, Prevention, Physical,

Mechanical, Cultural, Biological, Chemical, IWM

Methods of Weed Control

•Prevention

•Physical/Mechanical

•Cultural

•Biological

•Chemical

• IWM – Integrated Weed

Management

Weed Prevention

•Prevent arrival

•Prevent establishment

•Prevent Spread

Preventive Weed Control

1. Clean equipment

2. Irrigation water/canals/ditches

3. Soil

4. Organic Matter/Compost

5. Weed seed/seed quality

6. Spot treat/hand pull/herbicide resistance

7. Neighborhood cooperation

1. Clean Equipment

2. Irrigation Water/Canals/Ditches

Lack of weed control

on canals and ditches.

3. Soil

Virgin River St. George – Dec 21, 2010

4. Organic Matter/Compost

Temperature 140 F or more

Estimated hours required to kill 90% of seeds (after Dahlquistet. al., 2007)

Temperature (°F)

140 122 115 108

time required to kill 90% of seeds (hours)

Annual sowthistle

<1.0 2.1 13.3 46.5

Barnyardgrass <1.0 5.4 12.6 unaffected

London rocket <1.0 4.0 21.4 83.1

Common purslane

1.3 18.8 unaffected unaffected

Black nightshade

2.9 62.0 196.6 340.6

Tumble pigweed

1.1 107.0 268.5 unaffected

5. Weed Seed/Seed Quality

Seed Certification

6. Chemical – Spot treatment/selectivity

7. Neighborhood Cooperation

Neighborhood Cooperation

Neighborhood Cooperation

Neighborhood Cooperation

One year’s

seeding

equals seven

years

weeding!

Those who say

“Work well done

never needs redoing”

never weeded a garden

Summary

• Weed defined

• Plant Life Cycle

• Annual (winter or summer)

• Biennial

• Perennial (simple or creeping)

• Methods of Control – prevention,

physical/mechanical, cultural, biological, chemical, IWM

• What is that Plant?

• Why is it There?