[permaculture] Plant extracts for weed suppression

Steve Diver steved at ncat.org
Wed Jun 15 14:18:27 EDT 2005


Here is a recent literature citation I came across.

They used chemical solvents, followed by
germination inhibition bioassays to see how
well plant extracts suppress weed seeds,
followed by capillary electrophoresis to
determine active metabolites.

The plant extracts used in bio-organic and natural
farming sytems are simple plant teas made by
soaking leafy material in water, or enhanced extracts
prepared with microbial inoculants, molasses, and rock
dusts.  They are more commonly used for insect and
disease control.

The use of plant extracts for weed suppression
is mostly the domain of speculation and research.

Farmers have time to think while they are riding
the tractor or working vegetable beds all day long.

It could result in a few people fooling around with
soil-applied plant extracts, followed by observations
on weed emergence.

Steve Diver
Fayetteville, AR

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Journal of Environmental Science and Health, Part B:
Pesticides, Food Contaminants, and Agricultural Wastes

Publisher:  Taylor & Francis
Issue:           Volume 40, Number 1 / January 2005
Pages:       77 - 84
DOI:           http://dx.doi.org/10.1081/PFC-200034234

Allelopathic Potential and Systematic Evaluation of Organic
Extracts from Canavalia ensiformis Leaves (Jack Beans)

Sonia Santos, Maria de Lourdes Leite de Moraes, Antonio
Pedro da Silva Souza Filho, Maria Olímpia Oliveira Rezende

A1 Universidade de São Paulo, Instituto de Química de São Carlos,
São Carlos, São Paulo, Brazil
A2 EMBRAPA Amazonia Oriental, Belém, Pará, Brazil

Abstract:

This article describes the assessment of possible allelopathic potential
of organic extracts obtained from leaves of Canavalia ensiformis under
laboratory conditions. Furthermore, a systematic evaluation of these
extracts was carried out using specific protocols developed in capillary
electrophoresis (CE) to determine some groups of secondary metabolites.
After the identification and quantification of compounds, the effects of
compounds on germination of some common weeds was investigated,
which are becoming a real problem in pastures in the state of Pará, Brazil.

Keywords:

Allelopathy, Capillary electrophoresis, Herbicides and weeds



CONCLUSIONS

The results show that Canavalia ensiformis (Jack Beans) presents
a strong allelopathic potential and can be considered a source of
many compounds which, after having been studied properly, can
serve in the future like natural herbicides.

Organic crude extracts obtained from solvents with high dielectric
constants (dichloromethane, ethyl acetate, and methanol) were
more efficient in the bioassays. This fact suggests the presence
of polar compounds in the allelopathic phenomenon of Canavalia.
Methods followed in electrophoresis showed a high specificity,
which makes it possible to identify 4 classes of compounds
using the same crude extract samples, and analyse them
quickly (up to 20 min).  This can supply important information
about the composition of a specific plant, establishing in this
way, an important tool for preliminary listing of possible
present compounds groups.

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