Prof Steven R Belmain
Agriculture, Health and Environment Department
Natural Resources Institute
Faculty of Engineering and Science
University of Greenwich
Using pesticidal plants in
crop protection
Factors affecting plant material usage
Effectiveness
Cost
Availability
Toxicity
Ease of use
Acceptability
Versatility
Cost was considered most important
factor by farmers in Ghana
low cost high cost
Pesticidal plants usually do not kill insects quickly. Exposed
insects may take a few days to die. PPs can be toxic but also act
through repellency, anti-feedancy, growth regulation. Farmers
need to observe effects of PP application over longer time
periods. Results may not be as dramatic as experienced with
synthetic pesticide use.
Plant species identification, collection time, collection place,
processing method and application method can all make a
difference in how well a pesticidal plant works. For some plants
it doesn’t matter whereas others plants can be more variable.
We don’t have all the answers, but we do have some. Farmers
should be encouraged to experiment, e.g. establish efficacy
before widely using, try different plants, concentrations, mixing
different plant species together…
General rules and guidance on the use of
pesticidal plants
Sola et al. Guidelines for the Sustainable
Harvesting of Traditional Medicinal Plants in
Zimbabwe. SAFIRE, Harare, Zimbabwe 26 pp.
http://projects.nri.org/adappt/docs/HarvestingGuidelines.pdfhttp://proj…
Shade dry collected plant materials, exposure to sunlight will
often reduce efficacy
Store in dry, dark conditions until ready to use
Shortly before use, grind/pound/sieve to fine powder. This
increases extraction in water.
To make up an extract for spraying on a crop, add powdered plant
in water overnight to be used next day (approx. 24 hours). For
1%, add 10 grams powder per 1 litre water, for 10% solution add
100 grams per litre. Do not try to make extracts higher than 10%
(reduced extraction efficiency). Filter through cloth to remove
particles that will clog sprayer.
General rules and guidance for spraying
pesticidal plant extracts on field crops
Adding soap during extraction should be a general rule. Soap will
help extract compounds that are not water soluble. 0.1% soap is
made by adding 1 ml soap per litre. This also helps spread the
extract on the plant leaves more effectively.
Many compounds in plants break down quickly in sunlight. Spray
extracts in late afternoon or evening to maximise contact time
with insects.
Pesticidal plants need to be sprayed more frequently than
commercial synthetics – because of quicker breakdown and
because they often don’t kill all insects in one application.
Weekly spraying of several PPs has been shown to be as effective
as commonly used synthetics.
General rules and guidance for spraying
pesticidal plant extracts on field crops
Surfactant
Stops application
becoming droplets
Encourages
spreading/sticking
Encourages adsorption to
insects
Optimises extraction
Prevents nozzle clogging
What other reason is there for adding
soap to the extract?
Leaf surfaces are waxy
– like oils they are repellent to water.
SAFETY!!!!
1 ml soap per litre, 10 litre
bucket has 10 ml soap
10 g of plant powder per
litre = 1%. 100 g of plant
powder per litre = 10%
Make up day before use in
afternoon
Extract for 24h
Filter into sprayer
Spray in evening
Repeat spray weekly
Making extracts for spraying on field crops
For plant species that can
be sprayed at low
concentrations – 1% w/v
Make up with 10 ml soap
per litre and 100 g plant
powder per litre – 10% PP
with 1% soap
Then dilute down to 1%
PP with 0.1% soap
Higher soap increases
rate of extraction
Making extracts for spraying on field crops
Shade dry collected materials, sunlight will often reduce efficacy
Store in dry, dark conditions until ready to use
Shortly before use, grind/pound/sieve to fine powder. Admixed
powder with grain is more effective. But there may be good
reasons to use whole leaves or layering whole plants to more
slowly release volatiles or reduce grain tainting with powder.
Dipping in plant extracts combined with solarisation can be highly
effective, particularly for beans, cowpeas and other stored
legumes. Requires more labour and good drying conditions.
Depending on storage duration, may need repeated application
Wash / winnow grain that has been treated with PPs before
grinding / cooking
General rules and guidance for applying
pesticidal plants for post-harvest storage
Post-harvest storage questions
Do you store at household or quickly
sell?
Food
Seed
What would make you store more, for
longer? if you could manage pest
damage?
How do you currently control insects?
Is your grain dry enough
Grain gets harder as it
gets drier
Experienced farmers can
tell by
Biting
Pinching
Listening when
pouring or rattling it
Is your grain dry enough?
Materials required
A clean dry glass bottle of about 750
ml capacity with a cap that makes it
airtight
Some common salt
How to do it
Salt must be dry
Place the salt in hot sun in a thin layer
on some plastic sheeting for at least 3
or 4 hours - until the salt is hard
Turn the salt at intervals during this
time
Store the dry salt in a sealed container
Is your grain dry enough?
This is what you do when you are ready to do
the test
Fill one third of the dry bottle with the grain
sample (250g to 300g)
Add 2 tablespoons of salt (20g or 30g)
Close the bottle tightly with its cap or cork
Shake the bottle vigorously for 1 minute
Leave the bottle to rest for 15 minutes
If salt sticks to sides of bottle then moisture
content above 15% - not safe for storage
If salt does not stick to bottle then moisture
content below 15% - is safe for storage
Select an open area with no shade, sweep
the area to remove any stones or rubbish
Solarisation
Most effective low cost way
to control stored product
insects
Bring up a straw mat to
prevent heat being lost
into the ground
Lay the mat out so that it is
flat on a clean area of
exposed ground
Get hold of jute sacs and lay
them flat out all over the mat.
Solarisation
Pour cowpeas over the jute
sacs
Spread cowpeas over the jute sacs
evenly in a THIN Layer
Ideally cowpea should be one
grain deep but if space is short
not more than 2 cm.
First finger joint
Solarisation
Use stones to weigh down the edges
of the sheet and hold in place.
Place a large transparent plastic sheet
over the grain - FLAT.
Solarisation
Keep animals off and prevent heat escaping – ideally
every grain should touch the plastic sheet
Leave in the sun
for as long as it
is hot – 10
o’clock am to 3
o’clock pm.
Solarisation
Combining solarisation and pesticidal
plant extracts for stored grain
Mixing pesticidal plants
You will need a shovel and enough powdered
plant material to treat your grain
Make a heap of the grain
on a clean concrete floor,
tough plastic sheet,
tarpaulin or metal sheet
(not on bare earth)
Apply plant material
1 to 2 cups of plant
material to 100 cups
grain (1-2%). Try and
get advice for specific
plants.
Sprinkle powder all
over the heap of
grain, making sure the
wind does not blow it
away.
-similar to Acetllic/Actellic SC
Always wear a face mask/bandana to prevent inhaling powder.
Mixing pesticidal plants
Using a clean
shovel, gently mix
the powder into the
heap as well as you
can.
Mixing pesticidal plants
Shovel the heap to
another part of the
clean plastic sheet/
tarpaulin/ concrete
floor
Mixing pesticidal plants
Then shovel it back again.
Mixing pesticidal plants
Then shovel it back
again for a third time.
When you have finished
you shouldn’t be able to
see the plant material
Mixing pesticidal plants
Mixing pesticidal plants with maize cobs
or unthreshed millet, sorghum
For unthreshed grain
e.g. maize, millet or Sorghum
The tin can sprinkler can be
made using a clean tin with a
tightly fitting lid. About 10
holes should be made in the
lid of the tin using a 5 cm nail
or similar pointed tool
Apply in layers
Mixing pesticidal plants with maize cobs
or unthreshed millet, sorghum
Pesticidal plant species that are
Weeds, invasive, fast growing, perennials, easy to propagate
Woody, slow-growing, rare, difficult to propagate, over-
collected
Cultivated, food, spice, waste products
Weeds, invasive, fast growing, perennials,
easy to propagate
Azadiracta indica
Commonly called the Neem tree
Invasive and found across sub-Saharan
Africa, although distribution is patchy and
does not grow well in all habitats
Reported use in field pest management,
and post-harvest storage. Very high level
of evidence on efficacy when using seed
oil or seed powder. Leaves are much less
effective.
Many medicinal uses, timber, firewood
Fast growing and relatively easy to
propagate from seed
Azadiracta indica
Leaves can be collected anytime. Seeds must be collected when
they are fully ripe (yellow) and not yet fallen to the ground.
Seeds rapidly rot on the ground and become infected with
Aspergillus fungi that produce mycotoxins and such seeds should
not be used.
Main active ingredient, azadirachtin, is only found in the seed
and not present in the leaves. The oil can be pressed out of the
seeds or the seeds can be ground into an oily powder. The oil is
smelly and taints wooden processing equipment and, therefore,
often not extracted at the household level.
Neem oil can be diluted with water to 1% v/v and 0.1% soap for
very good efficacy. Neem oil should not be used in post-harvest
protection due to tainting and risk of mycotoxin contamination.
Azadiracta indica
Neem works as an antifeedant and growth regulator so don’t
expect immediate results. Insects will not quickly die and may
stay on the plant but not eat.
Extracts from dried leaves are best at higher concentrations, e.g.
10% w/v
Powdered leaves can be admixed with stored products, higher
concentrations necessary, e.g. 5% w/w
Safety issues: azadirachtin and other neem compounds have
been tested and shown to have no adverse effects on people.
There are several commercial products sold (USA, India, Canada,
China) and many medicinal uses and products, particularly in
India.
Melia azedarach and Melia volkensii
M. azedarach commonly called Persian
lilac or Chinaberry. M volkensii as Mukau
M. azedarach found across eastern and
southern Africa and considered invasive.
M. volkensii found across Ethiopia,
Somalia, Kenya, Tanzania
Used in similar ways to Neem
Valued for timber, some medicinal uses
Easy to propagate from seed
Safety: contains tetranortriterpenoids,
toosandanin. Chinaberry seeds are
poisonous to humans. Melia leaves more
effective pesticide than neem leaves.
Tephrosia vogelii
Commonly called fish bean plant
Native to Africa and well-distributed across
different habitats
Used in pre- and post-harvest pest management
and ecto-parasite control on livestock
Soil fertility/quality improvement through nitrogen
fixation and deep roots. Thus intercropped with
maize or used as cover crop and green mulch.
Leaves fed to livestock for de-worming and applied
to skin for skin diseases and tick/fly control, good
shade and boundary plant. Traditionally used to
kill/harvest fish.
Very fast growing and easy to propagate from seed
Tephrosia vogelii
Leaves are used
There are two chemotypes – one that works
and one that doesn’t – needs pre-testing by
farmer. Seasonal effects on chemistry are
known for some parts of Africa.
Follow general guidelines to make an extract.
Works as low as 1% solution. Adding soap
during extraction is important.
Also used post-harvest, working best with
stored legumes (1% w/w), less so with stored
maize pests.
Safety issues: contains rotenoid compounds.
Rotenone long used in agriculture with some
debate on safety to humans (based on historical
evaluation of refined commercial products)
Seasonal change in Malawi of T. vogelii leaf
composition of Deguelin and Tephrosin
C
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c.
u
g
/g
d
ry
w
ei
gh
t
Farmers need to harvest Tephrosia in January – in northern Malawi
0
100
200
300
400
500
600
700
800
Jan Mar Jun-10
Deguelin
Tephrosin
Optimising rotenoid extraction
from T. vogelii leaves
Methanol extract
5% Tween - soap
1% Tween - soap
Water
tephrosin
rotenone deguelin
Commonly called veld lupin
Native to eastern and southern Africa
Used in pre- and post-harvest pest
management and ecto-parasite control on
livestock
Large turnip-like root contains rotenoids and
used in same ways as Tephrosia vogelii leaves
Very fast growing and easy to propagate from
seed
As uprooting entire plant, should only harvest
from wild after seed production/dispersal
Dolichos kilimandscharicus
Neorautanenia mitis
Dolichos kilimandscharicus
Neorautanenia mitis
Root tuber is used
Root is dried and ground to powder
Follow general guidelines to make an
extract. Works as low as 1% solution.
Adding soap during extraction is very
important.
Also used post-harvest, working best with
stored legumes (1% w/w), less so with
stored maize pests.
Safety issues: contains rotenoid
compounds.
Lippia javanica
Commonly called fever tea tree, lemon bush
Woody shrub found throughout eastern and
southern Africa usually on forest fringe,
grassland on hillsides and stream banks
Used in pre- and post-harvest pest
management and ecto-parasite control on
livestock. High in essential oils with fumigant
effect
Leaves are used as a medicinal, herbal tea to
treat coughs and aching muscles, commercial
products available in some countries
Easy to propagate from seed or cuttings, can
be invasive
Lippia javanica
Essential oil chemistry varies dramatically both within and
between natural plant populations and this can have big impact
on efficacy. Geography and season affect chemistry. Farmers
should pre-trial before wide use
Taxonomy not quite clear, with several varieties
Some effort to commercialise essential oil pesticide derived
from Lippia in USA
Effect on tick count / animal when
treating cattle with 5% Lippia javanica
0
20
40
60
80
100
120
Tickbuster L. javanica Control
N
o
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ti
ck
s/
an
im
al
Relative quantities of components in Lippia essential
oil from 3 locations in Malawi - October
Location
Compound Nchenachena Chikangawa Jenda
Perillaldehyde 44 % 0 0.55 %
Limonene 24 % 0 13 %
Ipsdienone 1 % 52 % 31 %
Piperitone 2 % 0 22 %
Germacrene D 4 % 5 % 5 %
(+)-Carvone 3 % 0 0
Sub-species L. j. javanica L.j. whyteii L.j. whyteii
Contact toxicity of Perillaldehyde and
Ipsdienone against S. zeamais after 48h
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10
M
o
rt
al
it
y
(%
)
Concentration (mg/ml)
Perillaldehyde
Ipsdienone
Limonene, linalool, citronellal and perillaldehyde in
Nchenachena Lippia leaf oil over time
0
100
200
300
400
500
600
700
800
October December February April June
A
m
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t
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co
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p
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d
in
L
ip
p
ia
o
il
(m
g
/g
)
o
il)
Harvesting period
Limonene
Linalool
Citronellal
Perillaldehyde
Lantana camara
Commonly known as big sage, tickberry,
black sage, lantana
Highly invasive forming dense thickets,
toxic to cattle, out-competes / smothers
many local plant species, good mosquito
repellent if planted around houses
Extracts around 5% w/v are effective on
a wide range of crop pests, in post-
harvest admixed powders (2-5% w/w)
have been shown effective again maize
and bean weevils
Many sub-varieties with geographic and
seasonal differences affecting chemistry.
Farmers need to pre-trial with their local
sources
Vernonia amygdalina
Commonly called bitter leaf
Small woody shrub found across sub-
Saharan Africa
Many medicinal uses, de-worming
livestock/people, anti-malarial, anti-biotic,
vegetable, e.g. bitter leaf soup in Nigeria
Has been used to control fungal and
bacterial diseases on field crops and as
insecticide, best at higher extract
concentrations of 10% w/v
Easy to propagate, cultivated in some
parts of Africa
Dysphania ambrosioides
Commonly called wormseed, Jesuit's tea
Invasive weed throughout Africa
Used as spice in Mexican food, essential
oil used for de-worming, malaria
Used for post-harvest protection, often
using entire plants/leaves and periodically
agitating to release volatile compounds.
1% w/w works well for bean weevil, but
higher amounts (5% w/w) for maize
weevil. Extracts at 10% w/v have efficacy
against field pests
Easy to propagate, cultivated in some
places, commercialised as essential oil
pesticide in USA
Tithonia diversifolia
Commonly called Mexican sunflower or
Mexican marigold
Invasive weed found across eastern and
southern Africa along roadsides, field
margins, other disturbed habitats
Reported use in field pest management,
and post-harvest storage. Some good
evidence of general efficacy.
Medicinal, livestock fodder (leaves and
soft branches), firewood (woody
branches)
Easy to propagate from seed and cuttings
Tithonia diversifolia
Flower buds, open flowers and leaves are used
We don’t know how season/environment
affects efficacy
Follow general guidelines to make an extract.
Works as low as 1% solution, but better results
with 10% solution. Evidence of use on wide
variety of vegetable crops – tomato, beans,
brassicas
Also used post-harvest with maize and legumes
as admixed powder 1-5 % w/w
Safety issues: contains sesquiterpene lactones
and diterpenoids that have not been evaluated.
However, ingested as medicinal remedy.
Tagetes minuta
Commonly called southern cone marigold,
stinking roger, black mint, Mexican marigold
(as is Tithonia)
Found everywhere, highly invasive,
considered a crop weed in many places
A culinary herb in South America, herbal tea,
leaves can be irritant, growing it can remove
persistent weed species, good nematicide
Roots are nematicide and insecticide, leaves
are good insecticide. Extract at 1-5% w/v
effective against range of crop/soil pests.
Whole plants in post-harvest storage
Easy to propagate from seed
Tanacetum cinerariifolium
Commonly called Pyrethrum
Grown in highland areas (1,800 to 2,700
masl) throughout eastern and southern
Africa as a cash crop for natural pesticide.
Kenya used to produce 90% of world’s
supply – now Tasmania produces 90%.
Many established uses in all crops, post-
harvest, flea, tick, domestic/urban pest
control
Compounds are difficult to extract at local
level, but not impossible. Could be used
more widely in African agriculture. Access
to PyMarc ? – waste extraction product
Very easy to propagate and grow
Solanum incanum
Soft wooded shrub commonly called bitter
tomato, thorn apple, wild aubergine
Found throughout sub-Saharan Africa and an
abundant weed of disturbed and overgrazed
areas, road sides margins of woodland, riverine
and evergreen forest
Many medicinal uses, analgesic, antibacterial,
skin infections. Has been shown to cause skin
cancer so care should be taken when using.
Frui
