the use of organic herbicides

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Weed Management Society of SA

Third SA Weeds Conference 8-9 May

2012

The use of organic herbicides in

environmental weed control

Tim Marshall

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Tim Marshall

• Founder & first Chairperson of NASAA (first

Australian organic certifier)

• First IFOAM Standards & Certification

Manager (world peak body)

• Director of TM Organics

• Writer, trainer, consultant

• Weed, The Ultimate Gardeners Guide To

Organic Weed Control, ABC/Harper

Collins, 2010

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Tim Marshall

• TAFE Horticulture and chemical use

• Chemical Users Project (MLR)

• Local Government Training Authority

• Herbicide & alternatives (TMO)

• MLRCP(Manager Local Government)

• Revegetation (Greening Australia,

Regreen the Range, MLR Quarries etc)

Organic herbicides are only one technique applied by organic farmers with relevance to

environmental weed control

Thermal: flame, hot water, steam, black plastic (stolons), solarisation

Environmental manipulation (pH adjustment, Cation balancing, nitrogen restriction)

Alternative tillage

What are organic herbicides?

Organic herbicides are plant based

Include:

• Vinegar

• Plant essential oils and their extracts

What are organic herbicides?

Organic herbicides are plant based

Include:

• Vinegar

• Plant essential oils and their extracts

• BioWeed Control ® pine oil fractions

• Weed Zap ® clove, cinnamon & cottonseed oil, oleic & lauric acid, lactose & water

How do organic herbicides work?

• Dissolve the outer layer of leaves and seeds (lipids)

• Cause plants to desiccate (requires warm dry weather)

• Work very fast in temperatures above 30o

No resistance to organic herbicides?

• Conventional herbicides target chemical pathways within plants, stopping physiological processes

• Plants can dispose of, isolate or avoid chemicals and substitute other pathways to manufacture plant products

• Organic herbicides target fundamental plant structures –resistance requires overcoming millions of years of evolution

What are organic herbicides?

• Vinegar

• Extracts from plant essential oils

• BioWeed Control ® pine oil fractions

• Weed Zap ® clove, cinnamon & cottonseed oil, oleic & lauric acid, lactose & water

How are organic herbicides used?

Organic herbicides can be applied by

• Spraying

• Painting

• Soil drench (to control seed)

Organic herbicides do not affect lignified (woody) plant parts including stems and plant roots

How are organic herbicides used?

Organic herbicides are not selective in their action but they can be selective in use

• Remove rosette stage from native grass (growing point of grass is protected versus wide target area of rosette)

• Stop seed production

How are organic herbicides used?

Organic herbicides are fast acting (15 minutes) when temperature is high (especially if humidity is low)

The short time-frame for effective kill means field workers can observe the effect of their actions without having to return to the field a week later (as with glyphosate).

How are organic herbicides used?

Organic herbicides have no withholding period (stock can be returned to pasture once plants are dry) and have a short period of activity in the soil

In normal use organic herbicides are exceptionally safe for operators

Disadvantages of organic herbicides

1. Organic herbicides are not selective

2. They require high temperature (and ideally low humidity)

3. They are expensive

4. They require high volumes of water, high volume pumps and large nozzles

Advantages of organic herbicides

1. Organic herbicides are very safe to use for the operator and in public areas

2. They work very quickly in ideal weather conditions

3. They do not harm plant stems or roots

4. They can be used to provide a selective action, & may be applied by spraying, painting or drenching

Availability of organic herbicides

Three or four commercial organic herbicides are available

• BioWeed Control (pine extract)

• Weed Zapp (clove and other ingredients)

• Slasher (synthetic pelargonium oil)

• Yates vinegar

In the US a variety of other products are based on clove, cinnamon and citrus oil

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