Considerations in

Developing Weed

Management

Strategies

Greg MacDonald

University of Florida

What Are Weeds?

• plant out place - any plant a weed

• Melaleuca--native tree in Australia, but south Florida…………………?

• Corn -- crop when planted, but weed when volunteers next year

• Most “weeds” are non-cultivated native or non-native plants

• plants that interfere with human activity

Important Moments in Weed Science History

• Humans began farming ______ B.C.

• Romans sacked Carthage – 100 B.C.

• Burning (Native Americans - Great

Plains)

• Orient - flooding practiced for centuries

• In 1733, a famous English agronomist

suggested growing crops in rows

Weedy Characteristics

• fast growing, quick invasion potential

• reproduce quickly through lots of seeds, fragments, etc.

• easily spread through a variety of dispersal mechanisms

• lack of pests/problems to limit growth

Weed Management

• Preventative

• Cultural

• Biological Integrated Approach

• Mechanical

• Chemical

Preventative• don’t allow introduction, spread

• weed-free seed/transplants, certified seed

• legislation - noxious weed lists

Cultural

• create optimum conditions – hydrology, burn cycle

• prevent disturbance, allow natural

conditions to persist

• need to better understand ecology

to manage natural areas– seedbank dynamics

– natural disturbance mechanisms

BiologicalThe use of a biological

organism to provide

control of another

biological organism

……….resulting in low

levels of both species

Biological• Ecological – once introduced,

the species can maintain itself and become a part of the whole ecosystem

• Applied – continual introduction of the organism to provide control

Mechanical

• plowing, chopping, mowing, sawing,

hacking, sawing, burning, flooding….

• greater the intensity and duration;

see a shift towards more annual

species

• selectivity, specialized equipment,

labor intensive, $$$

Roller Chopping Native

Rangeland

Weed Management

• Preventative

• Cultural

• Biological Integrated Approach

• Mechanical

• Chemical

Herbicides 101……

Integrating the

Chemical Aspect into

Management

Chemical - Herbicides

• over 150 active ingredients registered

• close to 4000 trade names

• herbicides account for 55% of

pesticide use

Herbicide History

• Carthage - 100 B.C. (salted the ground)

• Copper SO4, sulfuric acid, salts - late

1800s

• petroleum oils, Stoddard’s Solvent- 1900’s

• 2,4,6-dinitrophenol - 1932

• 2,4-D -1944

The ‘Perfect” Herbicide

• Apply at any rate, any time, whenever and

wherever you want to.

• No protection required; totally non-toxic and

tastes like beer

• Controls the target plant, whichever that is

• Control lasts as long or little as we want

• Costs $1 per acre

Herbicide Use – Considerations

EfficacyPlant ID?

Control the target?

Toxicology

No water, hiking,

animal exposure

restrictions.

Non-target plants

Water use

Persistence

Environmental

Fate

Herbicide

Herbicide Selectivity

• placement - keep it away from

desirable plant

• uptake - apply so it doesn’t get in and

move

• metabolism - some plants breakdown

herbicides but…. …

• target site is different

Persistence/Environmental Fate

• physical processes affect herbicide

persistence

– The more hot and windy, the more loss

through volatility

– The sandier the soil, the higher the

rainfall; the more leaching

Persistence/Environmental

Fate

• Chemical and biological processes

–photodecomposition

• high light, more breakdown

–hydrolysis

• More water, more breakdown

• Biological processes – microbial– high temperature and high humidity

Soil Activity!!

Upland Plant Herbicides* 2,4-D

Triclopyr (Garlon 3A, 4)

Aminopyralid (Milestone)

Aminocyclopyrachlor (Method, mixes)

Chlorpyralid, Fluoroxypyr (Transline, Vista)

Imazapyr (Arsenal, Chopper, etc.)

Metsulfuron (Escort)

Imazapic (Plateau, etc.)

Imazamox (Clearcast)

Glyphosate

Modes of Action

ALS

herbicides

Glyphosate

Growth

Regulators

What we use

Imazapyr

Glyphosate

Triclopyr

imazapyr

amincyclopyrachlor

imazapic/imazamox

aminopyralid

triclopyr

glyphosate

ALS

Growth Regulator

ALS

Growth Regulator

Growth Regulator

glyphosate

Cultural

Chemical

Biological

Prevention

Mechanical

Considerations • Money, money, money

• Time, labor, quality of labor

• Density, remoteness

• Equipment options

• Integrated options

• Species, abundance, other desirable

species, endangered species

• Site conditions – soils, hydrology

Considerations • Permits, neighbors, public access

• What is your end game?

• What are you trying to achieve?

• Management vs. eradication

• Accuracy vs. areas treated

• Restoration?

• Frequency of visits

Restoration

•When?–During the control of target

species…?

–Selectivity is key

Restoration

•How?–Rely on seed bank or natural

recruitment

–Actively transplant or seed

Restoration

•Scope?–Large areas or satellite sites

–How much can you manage?

Restoration

•End Results…….–Fully functional ecosystem

–What will the area be used

for?

Weed Management

• Preventative

• Cultural

• Biological Integrated Approach

• Mechanical

• Chemical

Meeting the challenge…………

Innovative

Meeting the challenge……….

Adaptive

Meeting the challenge ………

Hard-Driving

Meeting the Challenge…….

Passionate