project report comparing the effectiveness of weed slayer organic ...€¦ · environmentally...

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

(water grass), Sorghum halepense (Johnson grass), Sida acuta (broom weed), Tridax sp.

(button weed) and Parthenum hysterophorus (white top).

Average length and number of leaves on dicotyledon species were 10.6 cm and 9.75 leaves

respectively while average length and number of leaves on monocotyledon species were

11.16 cm and 9.5 leaves, respectively.

There were no significant differences in the total number or monocots, dicots or total weed

species density in the different treatment plots before herbicide application.

Figure 1, mean number of weed species in plots prior to herbicide treatments. Means

followed by the same letter are not significantly different at P ≤ 0.05.

At weeks one and two post herbicide application, all treated plots showed reduction in the

total weed density/m2. While total weed density decreased further in glyphosate and eugenol

treatments at three weeks post treatment, there was an increase in the paraquat treatment

when compared to two weeks after treatment. At four weeks post treatment, total weed

density decreased further in glyphosate treatment while there was an increase in both eugenol

and paraquat treatments when compared to three weeks post treatment. At five weeks post

treatment total weed density increased in all treatments when compared to four weeks.

Similar trends were observed for mean monocot and dicot species densities over the period

with the exception of the glyphosate treatment which showed an increase in the dicot species

at three weeks post treatment when compared to two weeks post treatment. This increase

continued up five weeks post treatment.

Figure 2: Mean total weed density/m2 of herbicide treated plots before and after treatment.

Statistical analyses showed that at week 1 post-treatment there was significant difference (p =

0.000) in total weed density/m2 between the untreated control and all the treated plots when

compared. There was also a significant reduction in the total weed densities of the eugenol

treated as well as the paraquat treated plots (p = 0.008 & 0.000 respectively) when compared

to the week before treatment. Glyphosate treatment showed no significant difference in the

total weed densities before and at one week post treatment (p = 0.114). The paraquat

treatment showed greatest reduction in total weed density after one week. Glyphosate first

showed significant reduction in total weed density at three weeks post herbicide treatment (p

= 0.045). Significant reduction in total weed species density was maintained in all treatments

up to four weeks post treatment. At five weeks post treatment there was a significant increase

in total weed species density (p > 0.05) in all treatments inclusive of the untreated control

when compared to previous weeks.

Mean Total Weed species Density for Individual Herbicide

Treatments over Five Weeks

Figure 3 Change in total weed density/m2 for each treatment over five weeks. The same

letters above the bars indicates no significant difference in the mean total weed species

density for LSD test where P ≤ 0.05.

All herbicide treatments showed significant reduction in the mean dicot density/m2 from one

to four weeks post treatment when compared to the control (p = 0.000). However; there was

no significant reduction (p > 0.05) in the total dicot density/m2 in the neither the eugenol nor

glyphosate treated plots over the trial period when compared to the before treatment densities.

Despite this, both eugenol and glyphosate showed significant reduction (p = 0.013 & 0.000

respectively) in the density/m2

of broomweed species one of the most dominant dicots in the

plot from as early as week one. Significant reduction was maintained up to four weeks post

treatment. Paraquat showed significant reduction in total dicot density/m2 from as early one

week post treatment. Paraquat also showed significant reduction in broomweed species

density from at one week post treatment. Total dicot density/m2 increased significantly (p =

0.000) in all treatments at five weeks post treatment when compared to four weeks post

treatment.

Mean Total Dicot Species Density for Individual Herbicide


Figure 4 Change in total dicot density/m2 for each treatment over five weeks. The same

letters above the bars indicates no significant difference in the mean dicot density for LSD

test where P ≤ 0.05.

Table 2: Mean total Sida acuta (broomweed) density/m2

for each treatment before and after

herbicide applications.

Time Treatment

Control Eugenol Glyphosate Paraquat

Before treatment 25.75 a

30.25 a

32.25 a

14.00 a

1 week post treatment 30.75 a

8.00 b

4.00 b

1.00 b

2 weeks post treatment 38.75 a

3.75 b

0.50 b

0.00 b


2.50 b

1.00 b

0.75 b


4.50 b

1.00 b

0.50 b


19.50 ab

13.50 b

16.25 a

The same letters indicates no significant difference in the mean total Sida acuta density

within treatment for LSD test where P ≤ 0.05.

All herbicide treatments showed significant reduction in the mean monocot density/m2 from

one to four weeks post treatment when compared to the control (p = 0.000). Both eugenol and

glyphosate showed significant reduction (p = 0.05 & p = 0.038 respectively) in total monocot

species density/m2 at three weeks post treatment when compared to before treatment density.

Glyphosate showed further significant reduction (p = 0.022) at four weeks post treatment.

Paraquat showed significant reduction from as early as week one (p = 0.000). This was

maintained up to four weeks post treatment. Eugenol showed significant reduction in water

grass species at two and three weeks post treatment (p = 0.027 & 0.034) respectively when

compared to before treatment while glyphosate showed significant reduction at three and four

weeks post treatment (P = 0.013 & 0.008 respectively). Paraquat showed significant

reduction in water grass at from one week post treatment. This significant reduction was

maintained up to four weeks post treatment.

Mean Total Monocot Species Density for Individual Herbicide


Figure 5 Change in total monocot density/m2 for each treatment over five weeks. The same

letters above the bars indicates no significant difference in the mean monocot density for

LSD test where P ≤ 0.05.

Table 3: Mean total Commelina diffusa (water grass) density/m2

for each treatment before and

after herbicide applications.

Time Treatment

Control Eugenol Glyphosate Paraquat

Before treatment 19.00 a

14.75 a

16.50 a

21.00 a

1 week post treatment 15.00 a

7.75 ab

16.25 a

0.75 b


3.50 b

11.75 ab

1.50 b


4.00 b

8.00 b

1.00 b


7.50 ab

7.25 b

2.25 b


14.00 a

10.50 ab

15.75 a

The same letters indicates no significant difference in the mean total Commelina diffusa

density within treatment for LSD test where P ≤ 0.05.

Comparison of treatments over the period showed significant difference in total weed

density/m2 between paraquat and eugenol at as well as between paraquat and glyphosate at

one week post treatment ( p = 0.04. & 0.025 respectively) while there was no significant

difference between glyphosate and eugenol (p = 0.806). Significant differences also existed in

the total monocot species/m2 between the paraquat and eugenol treatments and between the

paraquat and glyphosate treatments (p = 0.028 & 0.001 respectively) while no significant

difference existed between eugenol and glyphosate treatments (p = 0.068). There was no

significant difference in the total dicot species among the three herbicide treatment (p > 0.05)

for the duration of the trial. At two weeks post treatment there was no longer a significant

difference in total weed species/m2

among the different herbicide treatments (p > 0.05).

Significant difference was maintained for total monocot species between paraquat and

glyphosate treatments (p = 0.001) but not between paraquat and eugenol treatments (p =

0.151). There was however no significant difference between eugenol and glyphosate

treatments. At three weeks post treatment there was no significant difference among the

herbicide treatments for total weed species density/m2 or total monocot density/m

2 (p > 0.05).

This was maintained for the remainder of the trial.

Figure 6 Mean total weed species/m2

before and after herbicide treatments. For each week,

same letters above the bars indicates no significant difference in the mean weed density for


Figure 7 Mean total dicot species/m2 before and after herbicide treatments. For each week,

same letters above the bars indicates no significant difference in the mean weed density for


Figure 8. Mean total monocot species/m2 before and after herbicide treatments. For each

week, same letters above the bars indicates no significant difference in the mean weed

density for LSD test where P ≤ 0.05.

Discussion

Significant difference between total weed species density as well as total monocots and dicots

density in all treatments when compared to the control showed that all treatments were

effective at reducing the weeds present in the trial plots.

Eugenol (Weed Slayer) showed significant reduction in total weed density as early as one

week post treatment. This coincides with the label information stating that results can be seen

in less than a week but may take 10 to 14 days. While the reduction produced in total dicot

density was not significant when compared to before treatment, significant reduction in

broomweed species density, the most dominant dicot in the plots showed that the product is

effective against some dicot species. Significant reduction in total monocot species at three

weeks post treatment indicates that Weed Slayer does possess some level of broad spectrum

activity as advertised.

Comparison of eugenol with paraquat treatments showed that while both treatments produced

significant reduction in the total weed density in treated plots at one week post treatment

when compared to before treatment densities, this reduction was significantly different

between the treatments. Weed density was greater reduced in paraquat treatment than in the

eugenol treatment. However, at week two there was no longer a significant difference

between the treatments implying that while both treatments are effective at reducing total

weed species density, paraquat is a faster acting active ingredient. The two herbicides

produce significant reduction against broomweed species; however, paraquat also produced

significant reduction against total dicot species while eugenol did not, thus indicating that

paraquat is more effective against a wider range of dicot species than eugenol.

Comparing eugenol to glyphosate showed that while eugenol produced a significant

reduction in the total weed species density at one week post treatment when compare to the

before treatment density and glyphosate did not, the difference in the reduction between the

two treatments was not significant. This lack of significant difference between both

treatments was maintained throughout the trial for the total weeds, total dicot densities while

it existed four out of five weeks for the total monocot density. These results indicate

similarities between the treatments. While paraquat shows greatest reduction in weed species

density as early as week one and two post treatment, the greatest reduction is observed in

eugenol and glyphosate treatments at weeks four and five. Glyphosate is a systemic herbicide

therefore, based on the similar behaviour of eugenol it would also appear that eugenol is also

a systemic herbicide.

The surge in weed density in all treatments at week five is due to increase rainfall leading up

to that time. The first three weeks saw the area experiencing mostly dry conditions so weed

growth was poor during that period.

In conclusion, eugenol (Weed Slayer) demonstrates systemic activity and showed significant

reduction in total weed density up to four weeks after treatment under local conditions. It

produced results similar to glyphosate treatment, showing effectiveness against both dicot

and monocot species.

References

Ahuja, Nitina, Daizy R. Batish, Harminder Pal Singh and Ravinder K. Kohli. (2014).

“Herbicidal activity of eugenol towards some grassy and broad-leaf weeds.” Journal of

Pest Science. Doi: 10.1007/s10340-014-0570-x.

Amri, Ismail, Lamia Hamrouni, Mohsen Hanana, and Bassem Jamoussi. 2013. “Reviews on

Phytotoxic Effects of Essential Oils and Their Individual Components: News Approach

for Weeds Management.” International Journal of Applied Biology and Pharmaceutical

Technology 4 (1): 96–114. www.ijabpt.com.

Booth, B.D., Murphy, S.D., Swanton, C.J. 2003.Weed ecology in natural and agricultural

systems. Wallingford Oxon, UK: CABI Publishing

Brevis-Acuña, Juan Carlos. 2004. Assessing Spraying Performance and Weed Control Using

a Precision Weed Control System with Image-Vision. University of California, Davis.

Cutler, S, Thomas Tworkoski, and H Cutler. 2002. “The Synthesis and Biological Evaluation

of Eugenol Derivatives as Potential Herbicidal Agents.” In Plant Growth Regulator

Society of America Meeting.

Dhaouadi, Anissa, and Nafaâ Adhoum. 2009. “Degradation of Paraquat Herbicide by

Electrochemical Advanced Oxidation Methods.” Journal of Electroanalytical Chemistry.

https://doi.org/10.1016/j.jelechem.2009.09.027.

Grillo, Renato, Anderson E.S. Pereira, Caroline S. Nishisaka, Renata De Lima, Kathleen

Oehlke, Ralf Greiner, and Leonardo F. Fraceto. 2014. “Chitosan/Tripolyphosphate

Nanoparticles Loaded with Paraquat Herbicide: An Environmentally Safer Alternative

for Weed Control.” Journal of Hazardous Materials.

https://doi.org/10.1016/j.jhazmat.2014.05.079.

International Agency for Cancer Research. 2016. “Q&A on Glyphosate.” Accessed

September 16, 2019. https://www.iarc.fr/wp-

content/uploads/2018/11/QA_Glyphosate.pdf

Santos, Mónica S F, Gabriela Schaule, A Alves, and Luis M Madeira. 2013. “Adsorption of

Paraquat Herbicide on Deposits from Drinking Water Networks.”

https://doi.org/10.1016/j.cej.2013.06.008.

Tesfamariam, Tsehaye, S Bott, I Cakmak, V Römheld, and G Neumann. 2009. “Glyphosate

in the Rhizosphere-Role of Waiting Times and Different Glyphosate Binding Forms in

Soils for Phytotoxicity to Non-Target Plants.” European Journal of Agronomy 31 (3):

126–32. https://doi.org/10.1016/j.eja.2009.03.007.

Vaid, S., Daizy R. Batish, H.P. Singh and R. K. Kohli. (2010). “Phytotoxic Effects of

Eugenol towards Two Weed Species.” The Bioscan 5(3): 339-341.

project report comparing the effectiveness of weed slayer organic ...€¦ · environmentally...

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