MINISTRY OF INDUSTRY COMMERCE AGRICULTURE & FISHERIES Research & Development Division Project Report Comparing the Effectiveness of Weed Slayer™ Organic Herbicide against Two Conventional Broad Spectrum Herbicides Commonly Used in Jamaica Prepared by: Sherry-Ann Brown, Senior Plant Protection Officer Entomology Laboratory, Plant Protection Unit Collaborators: Natural Bio Organics Solution Limited, St. Thomas Reviewed by: Sheldon Elliott Senior Research Director, Plant Protection Unit Date: February 5, 2020
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MINISTRY OF INDUSTRY COMMERCE
AGRICULTURE & FISHERIES
Research & Development Division
Project Report
Comparing the Effectiveness of
Weed Slayer™ Organic Herbicide
against Two Conventional Broad
Spectrum Herbicides Commonly
Used in Jamaica
Prepared by: Sherry-Ann Brown,
Senior Plant Protection Officer
Entomology Laboratory, Plant Protection Unit
Collaborators: Natural Bio Organics Solution Limited, St. Thomas
Reviewed by: Sheldon Elliott
Senior Research Director, Plant Protection Unit
Date: February 5, 2020
Introduction
Weeds are a common problem encountered in the production of agricultural crops. They are
defined to be native or introduced species that have a perceived negative ecological or
economic effect on natural or agricultural systems (Booth, Murphy and Swanton 2013). They
possess properties such as a rapid growth rate and high reproductive capacity that make them
strong competitors for cultivated crops. Weeds pose several threats such as reduction in crop
yields by competing with cultivated crops for space, light, nutrients and water, acting as hosts
for crop pest and diseases as well as interfering with field access and harvesting. As a result
of these negative impacts, it is necessary to control weeds in agricultural fields. One of the
most common practices for weed control in Jamaica and worldwide is the application of
synthetic herbicides. Two of the most commonly utilized active ingredients (a.i.) are
Glyphosate and Paraquat.
Glyphosate is a popular non-selective, broadband herbicide used on the market. It has many
uses from no-tillage cropping systems to precision agriculture (Brevis-Acuña 2004). After
foliar application, it is absorbed by the foliage and translocated throughout stems, leaves and
roots of the entire plant, finally accumulating preferentially in young growing tissues. The
herbicidal effect is based on inhibition of the shikimate pathway enzyme 5-
enolpyruvylshikimic acid-3-phosphate synthase (EPSPS), involved in the biosynthesis of
aromatic amino acids and phenolic compounds (Tesfamariam et al. 2009). Despite its
usefulness studies have shown where the potential of glyphosate to have possible negative
effects on human health. In 2015 the International Agency for Cancer Research (IARC)
classified Glyphosate as “probably carcinogenic to humans” (IARC 2016).
Paraquat’s popularity is related to its quick and non-selective action to kill green plant tissue
upon contact. Additionally, some studies proved that this compound is one of the few
herbicides capable of controlling the growth of weeds that became resistant as a result of
over-use of non-selective glyphosate herbicides (Santos et al. 2013). Paraquat is a bi-
quaternary ammonium salt that is normally synthesized in the form of the dichloride salt
[1,2], it has defoliating and desiccating properties. Its mode of action is based on the
inhibition of Photosystem I, by interfering with intracellular transfer of electrons in
photosynthesis. Half-lives of 16 months and up to 13 years have been reported for paraquat
adsorbed to soil under laboratory and field conditions, respectively (Grillo et al. 2014). It is a
dopaminergic neurotoxin implicated in selective striatal damage and degeneration of the
nigrostriatal dopaminergic pathway, leading to pathogenesis of neurodegenerative diseases
with behavioural abnormalities and loss of motor functions. Several epidemiological and case
control studies revealed that paraquat exposure has a strong correlation with an increased
incidence and development of Parkinson’s disease (Dhaouadi and Adhoum 2009).
While both paraquat and glyphosate has been proven as effective broad spectrum herbicides,
their possible negative impacts on human health necessitates the need for more
environmentally friendly and safer weed control methods including the use of organic
chemicals. Eugenol a natural compound extracted from the leaves, flower buds and stems of
the clove tree is reported to possess herbicidal activity towards a wide range of weed species.
Eugenol has little or no residual activity is considered environmentally safe. Eugenol damage
leaves by increasing cell membrane permeability, which caused membrane damage resulting
in significant leaf injury (Cutler, Tworkoski, and Cutler 2002). It was suggested that eugenol
may cause disruption of mitotic activity by microtubule disorganization or alteration of cell
wall biosynthesis (Amri et al. 2013). Under laboratory conditions, this compound produced
significant reduction in root and shoot lengths of both grass and broadleaf weeds (Ahuja et al.
2014). Vaid et al. (2010) also reported reduced root and shoot lengths of weed species treated
with eugenol as well as reduced weed seed germination. Based on these studied eugenol
appears to be a suitable alternative to synthetic herbicides in managing weed populations in
cultivated crops.
The objective of this study was to compare the effectiveness of the organic herbicide Weed
Slayer ( a.i. Eugenol) with two conventional herbicides (a.i. Paraquat and Glyphosate) for its
broad spectrum herbicidal activity under local conditions.
Methodology
A site was selected at the Bodles Research Station, St. Catherine and sixteen plots, each 4 x 4
m2
laid out using a completely randomized design. The layout consisted of four treatments of
glyphosate, four paraquat, four eugenol and four untreated controls. Eugenol is the a.i. in
Weed Slayer, the organic herbicide being evaluated.
Table 1: Plot layout of herbicide trial
Glyphosate
Eugenol
Eugenol
Paraquat
Control
Control
Glyphosate
Control
Glyphosate
Paraquat
Paraquat
Glyphosate
Eugenol
Control
Paraquat
Eugenol
An initial weed assessment was conducted prior to the application treatments.Using a 1 m2
quadrant the weed density per m2 was determined in each plot. Ten plants were randomly
selected and the number of leaves present on each counted. Treatments were applied to the
plots two days later using a backpack sprayer with a fan nozzle at the manufacturer’s
recommended rates.
Post-treatment weed assessments were carried out once weekly as described above for five
consecutive weeks after herbicides applications. Data collected was analysed using Statistical
Software for Social Sciences (SPSS) version 20.
Results
Weed assessment activities showed the presence of both monocotyledon and dicotyledon
weed species in the trial plots providing different weed types on which broad spectrum
herbicide activity could be tested. The most common species present were Commelina diffusa