The growing demand for essential oils for agricultural Applications

1. The Growing Demand for Natural Products in Agricultural
Applications
Mohamed Murray Hunter
School of Bioprocess Engineering
Northern Malaysian University College of Engineering
Introduction
Essential oils are a source material for the manufacture of fragrances, flavours and
pharmaceuticals and is a centuries old industry. The flavour and fragrance industry once
completely relied on natural materials until the 1930’s, when synthetic materials began to gain
acceptance. The development of synthetic materials acted as a catalyst in changing the
nature of the cosmetic and food industries, allowing much wider fragrance and flavour use in
end-products. This was due to lower cost of synthetic materials, the increased stability over
wider pH ranges they offered, better resistance to oxidisation, and the elimination of dis-
colourations in products, which had plagued natural fragrances1. This changed cosmetics
from being a product for only the wealthy, to being a product that all could afford. However,
this also dampened growth drastically for natural products, as society became fascinated with
the ‘brave new’ synthetic world of chemistry. Likewise, before the 1980’s, natural plant
extracts were only a novelty until manufacturers of cosmetics, personal care and household
products realised the marketing potential of these materials for ‘green’ product positioning.
Lifestyle changes in the West, enhanced through rising incomes and standards of living
propelled many natural and tactile therapies into peoples’ lifestyles, thus bringing resurgence
in demand for essential oils and other plant extracts again.
The 1980’s and 90’s saw the golden age of pytho-entrepreneurship, where essential oil, herb
and plant extract production boomed and almost went unchecked by the regulatory
authorities. People began growing ginseng in their garages, selling them in the open market
and growing all sorts of new exotic herbs and essential oils until marketing claims became
totally outrageous. The EU introduced heavy regulation, the US FDA became much stricter
and most countries in South-East Asia developed their own version of the FDA or enacted
legislation controlling this industry. Now the essential oil, herb and plant extract trade is falling
back into the hands of the larger international manufacturers and traders, who have the
resources to deal with regulatory authorities, eliminating the opportunities existed during
those two decades.
Other than natural market growth, around 3-5% per year, there is no real growth for essential
oils and plant extracts in their traditional markets, and certainly very little opportunity for any
new essential oil or plant extract to be developed internationally, on a large scale.
However, the same cannot be said for the use of essential oils and plant extracts in the
agricultural market. Agriculture itself is currently undergoing a revolution with major changes
in practices taking place. Agriculture is being redefined. Those involved in agriculture once
held the view that the environment can be totally controlled through fertilisers, pesticides,
herbicides, hormones and trace elements. However accepted practices began to show their
shortcomings and basic assumptions about agriculture re-questioned. Evidence showed
conventional practices led to phosphates, heavy metals and herbicides seeping into water
tables, crops absorbing unsafe levels of chemicals and land just failing to provide satisfactory
yields, due to unsustainable practices. In some cases, agricultural communities have just
been wiped out and ceased to exist or continued to operate with negative capital returns.
As a result, Agriculture has gone back to the future, farmers re-evaluating the ways, practices
and methods of the past. New paradigms have been developed with the catch phrases of
‘sustainable’, ‘integrated’, ‘organic’ and ‘balanced eco-system’. The ‘new-age’ farmer is much
more sensitive to the eco-system that supports the viability of the enterprise and as a
consequence is beginning to use a much wider information base to make decisions, with a
holistic orientation, understanding in great detail relationships between ‘inputs’ and ‘outputs’,
focusing on balance.

2. Agriculture was once a so precise science that farmers believed they knew what remedy to
use for what problem and even knew how to prevent these problems through establishing
precise and disciplined preventative regimes and methods. Modern science provided this
sense of confidence with hi-tech solutions such as using geo-stationary satellites to predict
crop yields and insect plagues and through land sensing, could advise what fertiliser, how
much, and when to apply it, to obtain the planned yield. A massive agro-chemical business
evolved, providing all the technical answers needed, dominated by strong trans-national
companies, where almost total oligopoly competition exists.
The New Age of Agriculture
Three main factors are forcing change in agriculture.
Firstly, consumers have become much more aware of what they are eating and want food
that is free of toxic chemicals, heavy metals, hormones and the like. These issues are being
scrutinised so closely these days that consumer groups have put up such a fight against the
introduction of genetically modified (GM) crops out of fear that changed DNA, may have some
unknown and undesirable long term health effects on consumers2. In sensitivity to the
consumer, some companies are even labelling food as non-GM. This awareness is spurring
the rapid growth of organic foods, where “organic farming is practiced in approximately 100
countries throughout the world, with more than 24 million hectares (59 million acres) now
under organic management. Australia leads with approximately 10 million hectares (24.6
million acres), followed by Argentina, with approximately 3 million hectares (7.4 million acres).
Latin America has approximately 5.8 million hectares (14.3 million acres) under organic
management, Europe has more than 5.5 million hectares (13.5 million acres), and North
America has nearly 1.5 million hectares (3.7 million acres)”3. Further, organic farming has
shown an increase of 20% per annum over the last decade and now approximately 2% of the
4
U.S. food supply is grown using organic methods . The global market for organic food and
5
drink reached $23 billion in 2002 .
Secondly, conventional agriculture in Malaysia has caused eco-system contamination,
particularly in the water tables and ponds located in agricultural areas. Land also contains
traces from build up of residual chemicals used in agriculture.
Thirdly, to maintain sustainability of farms, the strategy of applying more chemicals in the form
of pesticides and fertilisers was pursued. Land is not being rotated and topsoils are being
eroded, thus requiring more nutrient replenishment, which continues to increase the cost to
achieve the same yields, each year, in a vicious circle.
The first factor indicates a distinct shift in consumers tastes and habits, which is leading to
changes in demand – this is a long term shift. To be viable and survive, a farmer must supply
according to demand, or the enterprise will soon go out of business. This is the invisible hand
that determines what should be produced, consumer trends must be heeded by farmers or
the farm enterprise will be marginalised. The second and third factors combined are eroding
profitability, making farming more marginal and unsustainable in the long term. This factor is
threatening survival from the supply side. These factors combined, the market in an economic
sense, is forcing a change in the approach taken to farming, as its very survival will depend
on it – it is a structural change. Those that read the market correctly will survive and prosper,
those that don’t will not survive. The little bit of evidence that supports this argument is the
dramatic growth of certified organic farms in Malaysia between 2001 and 20026.
This changing approach to agriculture is redefining the framework that farmers now view field
management. The old and new paradigms are summarised and compared in table 1 below7;

3. Comparison of the Industrial and
Biological Models of Agriculture
Industrial Model Biological Model
Energy Intensive Information Intensive
Linear Process Cyclical Processes
Farm as a Factory Farm as an Ecosystem
Enterprise Separation Enterprise Integration
Single Enterprise Many Enterprises
Monoculture Diversity of Plants and Animals
Low-Value Products Higher Value Products
Single Use Equipment Multiple Use Equipment
Passive Marketing Active Marketing
These approaches require a completely new approach, in regards to the types of chemicals
used. Agricultural chemicals must now support the eco-system (i.e., prevent further
contamination and pollution of the water tables), add value, promote sustainability and assist
in providing long term profitability.
The New Tools of Trade
Only certain types of fertilisers and pesticides are allowed in organic farming, including those
derived from micro-organisms and materials derived from plants, animals, or mineral bearing
rocks. Soaps are also allowed under many certifying authorities. Generally, pesticides and
soaps allowed for organic farming are those that will break down quickly and non obtrusive to
the eco-system. The discussion will now turn to some of the types of materials used in
organic and sustainable farming.
1. Enzyme catalysts and Fertiliser/Insecticides
The use of enzymes as catalysts to produce composts and organic fertilisers is widely
practiced in Australia, Europe, US, India and Thailand. By definition, this is a practical
8
application of bio-process engineering . In Thailand, where organic agriculture is quickly
advancing, many farmers have been taught the skills and acquired the knowledge to produce
their own enzymes for use as a catalyst to produce fertilisers through the fermentation
process. By adding certain other ingredients into this process like the leaves and fruits of
neem, citronella grass and tobacco leaves, fertiliser/insecticides can be made. Other products
like Pseudo Hormones are also made using variations of the basic enzyme formula to
promote flowering and the production of fruit.
Local production of these enzymes developed because the importation of bokashi
(photosynthetic organisms, lactobacillus) was too expensive to purchase. Consequently, the
production of enzymes developed through trial and error and experience, rather than
scientifically. Farmers develop their own fermentation formulae, which suits their particular
purposes, specific to their geographical locations, crops and raw materials available. This of
course means that the relative activity of different products will vary greatly depending on the
skill and knowledge of individual farmers.
The basic ingredients in the production of the ‘EM’9 include fruits, vegetables and animal
waste. Fruits are rich in natural enzymes, which act as a catalyst to ripen and then
disintegrate the same. Different fruits will produce different enzymes (i.e., citrus fruits ascorbic
acid oxidase, pineapple bromelase, tomatoes pectinase, and papaya papain). Vegetables
produce other enzymes, which like the fruits catalyse cellulose in the leaves to crispness and
later softness and disintegration (i.e., sweet potatoes beta-amylase, leafy vegetables
chlorophyllase and phenolase). Animal waste will produce yet other enzymes (i.e.,
peroxidase, elastase, lactase, etc).
The primary enzymes that are produced at farm level are proteases in the form of bromelase
from pineapples (Ananas comosus) and papain from papaya (Carica papaya). Bromelain is
really a collection of similar protease, which are good protein digesting enzymes. Papain is

4. also good at breaking down fibrous substances. These are important qualities in producing
composts and fertilisers. The table below shows a general formula for enzymes produced at
village level. As mentioned previously, most people will have their own proprietary methods
and ingredients.
A General Enzyme Base for Fertiliser production
Banana, grape, Pineapple, apple, orange, 6 kilograms in various proportions
papaya, Mango stein according to person’s own formula
Molasses 3 kilograms
Water 20 kilograms
Chicken or cow manure 3 kilograms
Procedure: Place all ingredients together in a
sealed tank and mix. Leave for at least one
week. This process can be sped up by
placing an existing enzyme in the mixture.
Once this base enzyme is ready, it can be used in the preparation of solid or liquid type
fertilisers. Through varying the inputs into the fermentation process, it is possible to produce
specific groups of enzymic compounds, which can be tailored towards specific applications,
such as specific crops and soil types, while other products can be made by the household like
cosmetics and detergents. Some farmers are producing their own herbicides for controlling
weeds10.
Common Enzymes, Potential Sources and Other Potential Applications
Enzyme Potential Sources Potential Applications
Ascorbic acid Citrus fruits, leaf vegetables, Fruit preservation, cleaning
oxidase cucumbers applications
Beta-amylase Grains, sweet potatoes, taro, Yeast production
cassava
Bromelains Pineapples Fertilisers, pseudo hormones,
cleaning, cosmetics, personal care,
mouthwashes, skin healing, anti-
acne, anti-microbial
Catalase Animal wastes, milk wastes Cosmetic, anti-ageing, oxidising
Chlorophyllase Some leaf vegetables UV absorption
Elastase Animal intestines Cosmetics, anti-aging
Glucoxidase Some mushrooms, mould, other Anti-oxidant
fungi
Papain Papaya Fertilisers, wound and skin healing,
mouthwashes, other cosmetics,
dishwashing, all purpose cleaning

5. Preparation of the enzyme base in Sabah
The use of the enzyme in preparing solid fertiliser
2. Essential Oil Based Fungicides/Insecticides
A new generation of crop protection products is emerging in the market, based on a soap
and essential oil emulsion. These products take advantage of the anti-microbial
properties of tea tree oil (Melaleuca alternifolia) to function as a fungicide. Biomor of the
United States manufactures these products under the trademarks of Timor and
11
Tomorex . These products are certified as fully organic and are sold as fungicides and
insecticides. The company claims that these products can be tailor made to selectively
attack insects, leaving those beneficial alone. It is further claimed that these products
leave no residual and can fully negate the need to use copper or sulphur in field

6. application. The following photo shows the efficacy of the product on cucumber leaves,
12
compared to a control and commercially available synthetic .
Nimgard +
Kocide
Control
Timorex
0.5 % Timorex 1 %
The company solved the problem of essential oil volatility through patented encapsulation
processes13, and sales have rapidly grown to a turnover of USD 50 million per annum, within
the first three years of operation14, through South America, South Africa, Philippines, Greece,
Australia and the United States. According to the company sales growth is severely
hampered by the unavailability of enough tea tree oil to expand production.
3. Natural Anti-Stress Preparations from Betaines and Essential Oils
Degrading soil fertility, salinity, heavy metal residuals in the soil, and the effects of global
warming, are subjecting crops in many temperate countries to stress. This has created a
market for anti-stress products, which is slowly growing in importance to agriculture. The
essential oil of some trees, Meleleuca bractea for example, have been found to
substantially reduce the stress of crops15. Plant stress levels can be lowered by applying
betaines produced from methylated prolines, N-methyl proline, trans-4-hydroxy-N-methyl
proline and trans-4-hydroxy-N-dimethyl proline, extracted from various specifies of
Meleleuca16. A compound platyphyllol17, found in Melaleuca cajuputi, a native of
Malaysia, has ‘UV blocking’ attributes18, This could be used in treatment of plant stress,
as one of the major stressors of plants is UV radiation. None of these natural products
have been patented for this application or commercially produced at this point of time.

7. Melaleuca cajuputi trees in Terengganu
4. Plant Extracts: Neem based Products
Neem (Azadirachta indica A. Juss) is considered be many to be one of the wonder trees
in our global bio-diversity. Numerous uses for this tree have been both reported and
practiced by many indigenous peoples over the centuries. Neem is a major input in Thai
and Indian agriculture for the production of natural insecticides at farm level. Neem
contains a number of compounds of which two ‘steroid like’ molecules, azadirachtin and
19
salanin , exhibit very potent insect repellency attributes. Neem does not knock down
insects like conventional pesticides, but rather interferes with the lifecycles, confusing
them to the point they cannot reproduce and thus disappear20.
The potential for neem as an agricultural input is tremendous, however there are a
number of problems. Plantations of neem in Malaysia are very small, and even if there
were massive plantings today, they trees could not be used for 5 years. ‘Neem oil’, which
is not a true oil in the real sense but a tincture, can be extracted through solvents or
through soaking out the active ingredients in a bin or tank in water. The ‘oil’ or tincture
resulting, is very unstable and will lose activity within a relatively short period of time.
Standardisation problems have been found with neem oil is available from India, which
makes it difficult to use in large commercial operations practicing standard processes.
Finally, there is an unresolved health and safety issue as neem also has contraceptive
attributes, preventing neem from gaining registration as an agricultural material in many
countries. Even though, this issue could be addressed, there is no central neem industry
coordination group to raise finance to undertake the required research to produce a
monograph.

8. Neem Tree in Perlis
5. Plant Extracts: Pyrethrums
Pyrethrum based products are rapidly growing in demand for application as a pesticide in
agriculture. Under most jurisdictions it is organically certifiable. Pyrethrum is extracted via
solvents (usually hexane) from the flowers of Chrysanthemum cinerariifolium, which could
grow well in many highland areas of Malaysia. Natural pyrethrum used to be the major
active ingredient in household insecticides before the synthetic pyrethroids, which have
much longer residual effects were developed. Natural Pyrethrums are non-toxic to
humans and is known as one of the safest pesticides in use. The advantages of natural
pyrethrum is that it has a fast knock down effect on insects, through attacking the insect
nervous system, however the substance is very unstable in UV light, which breaks it
down very quickly. Pyrethrum is usually applied as a spray on crops during the growth
and maintenance periods.
Pyrethrum Daisy

9. 5. Essential Oils in Soap Bases
Citronella oil soaps became popular in the 1980’s as a way to control insects on flowers
and vegetables. This type of product was popular by a select group of nurseries and
horticulturalists at the time because of the non-residual properties and low toxicity of
these products. The efficacy of the product depended on suffocating insects during
spraying and causing enough irritation for them to abandon the host plants. Soaps with
essential oil additives are quite effective in intensive and confined areas, but of limited
use in extensive farming due to the number of repeated applications required to maintain
zero pest infestation. Variations of this product utilising eucalyptus, rosemary, pennyroyal,
clove, nutmeg and tea tree oil have come onto the market in recent years. This type of
formulation could be considered the forefather of the newer organic fungicides,
mentioned under the first heading. The author patented this formulation in 1986, which is
marketed under the brand Clensel in Australia, New Zealand and UK21, under license with
Jeyes UK Ltd.
Clensel Insecticide
Formulation
Water 86.09% w/w
Potassium hydroxide 2.02%w/w
EDTA 0.0879%w/w
Oleic acid 10.60%w/w
Citronella oil 1.099%w/w
Sodium carbonate 0.8798%w/w
Clensel Insecticide Label
7. White Oils
White oil is a name given to oils emulsified in a soap base. Any number of oils including,
paraffin, mineral oil, canola, caster, sunflower, can be used. These products are generally
used to remove various funguses and scales from plants and trees. Some people add
either ammonia or vinegar to the formulation to enhance the efficacy and add some insect
repellency and enhance crop greenness before harvest. In general use these emulsions

10. are sprayed over the plants. For diseased plants, they are manually applied and rubbed
around the infected areas of the tree to remove the fungus and scales. There are many
variations of this product on the market, with different philosophies and approaches.
Traditional oils like paraffin22 are used by many, however with the long CH2 chains, 30 in
this case, brings phototoxicity issues which can be potentially fatal to the plant. In addition
these long chain oils may carry sulphur residuals. Also the film created by these oils can
block the stomata (intake apparatus of the plant), preventing nutrients being taken up.
Some practitioners opt for the vegetable oils and create mild soaps with various additives
to assist in killing fungus spores and removing scales, like eucalyptus or tea tree oils.
A simple mild white oil formula with eucalyptus oil as an additive and preservative is
shown in the table below;
A Simple White Oil Formula
Water 58.0%w/w
Castor Oil 30.67%w/w
Potassium hydroxide 5.78%w/w
Eucalyptus Oil 5.55%w/w
8. Organic Dusts
Garden dust is a multi-purpose insecticide/fungicide made up with a bulking agent and
various synthetic and/or natural plant derivatives. Garden dust is used against plant
diseases like powdery mildews, bacterial blights, early blights, fire blight, anthracnose,
alternaria blight, leaf spot diseases, brown rot, apple cedar rust, peach leaf curl, peach
23
canker, stem blight, shothole, leafscorch, black rot, scabs and botrytis . Garden dust also
provides some repellency against a number of insects. The usual active ingredient is
rotenone, which is extracted from the roots, leaves and seeds of Derris elliptica, locally
available in Malaysia24. This product can be mixed with water and applied as a spray or
sprinkled over plants directly. Although most garden dusts are acceptable as an organic
product, it can leave toxic residuals and would be harmful if applied too soon before
harvest.
9. Organic Herbicides
The biggest single problem facing farmers in Malaysia is weed control. Organic
herbicides based on vinegars and essential oils have not even come close to matching
conventional herbicides as the results of a US study indicate, shown in the figure below25.
Most, organic herbicides on the market, generally rely on acidic pH and burning out the
grasses, which tend to produce spasmodic results. In a country like Malaysia, weed
control is a chronic problem, usually requiring very strong conventional herbicides to
counter extremely positive conditions for growth: warmth and high rainfall. In addition all
organic herbicides are general and non-selective at this point of time. Alternative
practices to using conventional herbicides are currently very limited and generally require
the use of extensive labour, which is expensive, i.e., mulches, plastic covering, selective
burning, etc26. Opportunities exist to develop efficacy improvements in organic herbicides
through other formulating routes like specific enzyme development.
Comparison of a conventional Herbicide with an Organic Herbicide on the US
Market
Product Reported Results*
Control O
27
Round Up Pro 10
All-Down Organic28 Range 0.5 – 3.8

11. *1-10 with 10 = best after 10 days
Conclusion
The advantages of focusing on natural product research and development for application in
the agriculture sector are many. Unlike, cosmetics, flavour and fragrance ingredients and
pharmaceuticals, the costs of product registration are both cheaper and require much less
data. Field efficacy trials for agricultural products are much cheaper and easier to manage
than clinical trials for cosmetics and pharmaceuticals. The technologies, as discussed above
are much easier and straight forward. The global agricultural market is much more
fragmented than the flavour and fragrance and pharmaceutical industries, so this would allow
much more ease in market entry for any future commercial product produced. Also of great
importance, is that this region is one of the largest consumers of agricultural inputs, so it is not
necessary to crack the European or US market straight away – there is plenty of business for
these products locally before we go abroad, which is the opposite case for cosmetic
ingredients, flavour and fragrance materials and pharmaceutical ingredients.
Competitive advantage can be gained through standardisation methods and in Malaysia we
have the expertise to undertake this without outside assistance. Through standardisation and
proprietary methods of manufacturing and processing to a standard set by us, intellectual
property can be developed, which will further develop barriers to entry to other potential
producers. The established multi-national companies in the agricultural input market, have a
big disadvantage. These organisations are geared to factory and process manufacturing. In
contrast, the production of organic products tends to rely on securing sources of materials,
which are firmly under our control. This advantage, will give a local manufacturer time to start
up, develop the market, before large scale competition enters the market with direct
substitutes.
The new age farming discussed at the beginning of this article is rapidly growing and the
market for agricultural input products is in excess of USD 50 billion and steadily growing. This
is surely an opportunity that Malaysia’s natural product, biotechnology and agricultural
researchers could focus on.
1
Hunter, M., The use of natural fragrances in cosmetics – should it be considered?, Cosmetics,
Aerosols & Toiletries in Australia, Vol. 19, No. 3., (1996), P. 39.
2
BBC, GM Crops: An Action Network Briefing, http://www.bbc.co.uk/dna/actionnetwork/A2418509
(accessed July 2006)
3
The World of Organic Agriculture 2004-Statistics and Future Prospects, February 2004.
www.soel.de/inahlte/publikationen/s/s_74.pdf (accessed January 2006)
4
Published by the Natural Marketing Institute, in partnership with the Organic Trade Association,
http://www.ota.com/consumer_trends_2001.htm (accessed January 2006)
5
The Global Market for Organic Food & Drink, July 2003, Organic Monitor
www.organicmonitor.com/700140.htm (accessed January 2006)
6
Ramli, B., The development of organic farming in Malaysia, paper presented at the Workshop on
Green Productivity and Natural Farming, Seoul, Korea, organised by Asian Productivity Organisation
(APO)
7
Sullivan, P., Applying the Principals of Sustainable Farming: Fundamentals of Sustainable
Agriculture, Davis California, ATTRA, 2003, P. 2.
8
University of Nebraska Lincoln, The Department of Biological Systems Engineering,
http://bse.unl.edu/
9
This is the local name given to enzymes as a generic term
10
Hunter, M., and Yothangrong, K., The Emerging Cosmetic & Personal Care Cottage Industry in
Thailand: The Production of Enzyme Based Products, Cosmetics, Aerosols & Toiletries in Australia,
July 2006, in press.

12. 11
Registered Trademarks of Biomor http://www.biomor.com/solutions.htm#e
12
Photo courtesy of Mr. Peter Tirosh
13
Currently 5 patents (1 approved and 4 pending)
14
Private communication with Mr. Peter Tirosh, owner
15
Naidu, B., P., Production of betaine from Australian Melaleuca spp. For use in agriculture to reduce
plant stress, Australian Journal of Experimental Agriculture, 43, 2003, pp. 1163-1170,
16
Bodapati, P., Naidu, P. and Cameron D., F., Reducing Plant Stress Using Australian Melaleuca, A
Report for the Rural Industries Research and Development Corporation, Canberra, RIRDC, 1999.
17
Brophy, J. and Doran, J.C., Essential Oils of Tropical Asteromyrtus, Callistemon and Melaleuca
species, Canberra, Australian Institute for Agricultural Research, (1996), P. 63.
18
Yaacon, K.B., Abdullah, C.M., and Joulain, D., Essential Oil of Melaleuca cajuputi, Paper presented
to the 11th International Congress of Oils, Fragrances and Flavors, New Dehli, India, 12-16th November
1989.
19
Report of an Ad Hoc Panel of the Board of Science and Technology for International Development,
Neem; A Tree for Solving Global problems, Washington D.C., National Academy Press, 1992, P. 34.
20
Ibid., P. 39
21
Australian Patent No. 617648
22
CH3(CH2)30CH3
23
http://www.ghorganics.com/Garden_Dust_Insecticide_Fungicide.html
24
Burkill, I. H., A Dictionary of the Economic Products of the Malay Peninsula, London, Government
of the Straits Settlements, Volume 1, 1934, pp. 795-808.
25
Ferguson, J.J., Evaluation of Organic Herbicides, Horticultural Sciences Department, University of
Florida, Gainesville,http://www.hos.ufl.edu/jjfnweb/organicnl/Dec03/JJF%20Evaluation_Art1.htm
(accessed July 2006)
26
Sivapragasam, A., Management of Pests, in Aini, Z., Sivapragasm, P., Vimala, M.N. and Mohamad
Roff (eds.), Organic and Vegetable Cultivation in Malaysia, Kuala Lumpur, MARDI, pp. 109-110.
27
Registered Trademark of Monsanto.
28
http://alldownherbicide.com/