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Sign and symptoms in
crops
Dr. Kumara Thevan
FIAT, UMK
Overview
• Affected plant parts
• Diseases
• Diagnosis plant pest (beneficial &
pest insects)
• Pest infestation (assessment)
• Stored product pest
Pest damage to crop plants
Vegetables
“Tomato, are you health or not?”
• Environmental stress• Nutritional deficiency
• Chemical injury
• Insect damage
• Infectious Disease: fungi, viruses, bacteria, nematodes
Nutrient Deficiencies
Iron
Calcium Molybdenum
Magnesium
Disease triangle
HostSpecies
Cultivar
Age
Pathogen
fungi
bacteria
nematodes
viruses
EnvironmentTemp, RH, wetness
Symptoms & Signs
Symptom
Expression of a disease by the plant
Sign
Visible presence of a pathogen
Symptoms
Galls
Leaf spots
Wilthttp://www2.dpi.qld.gov.au/horticulture/17902.html
Mottling, distortion
Signs: pathogen structures
Anthracnose
Tomato
Clemson University –
USDA Cooperative Extension Slide Series
www.ipmimages.org
Cabbage white mold mmk
Anthracnose
squash
Clemson University –
USDA Cooperative Extension Slide Series, ,
www.ipmimages.org
Alton N. Sparks, Jr., The University of Georgia, www.ipmimages.org
Vectors: whiteflies, aphids, thrips
Diagnosing Plant Pests
• The best way to control insects and
diseases to prevent them before they
get a foot hold in your garden.
• How?
Beneficial Insects
• Ladybug larvae are equally relentless predators.
…
• The Praying Mantis is anotherwidely-recognized insectpredator.
Lacewing Larvae
• They are miniature monsters when
viewed at close range. They are
deadly enemies of small caterpillars,
aphids, and other soft-bodied insects.
Chrysoperla carnea
Appearance
• Approximately 12–20mm long.
• Adults are pale green and have long
antennae and bright, golden eyes.
• They have large, transparent, pale
green wings and a delicate body.
Plants that attract LadybugsAchillea filipendulina - Fern-leaf yarrow
Achillea millefolium- Common yarrow
Ajuga reptans - Carpet bugleweed
Alyssum saxatilis - Basket of Gold
Anethum graveolens - Dill
Anthemis tinctoria - Golden marguerite
Asclepias tuberosa - Butterfly weed
Atriplex canescens - Four-wing saltbush
Coriandrum sativum - Coriander
Daucus Carota - Queen Anne's lace
Fagopyrum esculentum - Buckwheat
Foeniculum vulgare - Fennel
Helianthus maximilianii - Prairie
sunflower
Penstemon strictus - Rocky Mt.
penstemon
Potentilla recta 'warrenii’ - Sulfur
cinquefoil
Potentilla villosa - Alpine cinquefoil
Tagetes tenuifolia Marigold - lemon
gem
Tanacetum vulgare - Tansy
Taraxacum officinale - Dandelion
Veronica spicata - Spike speedwell
Vicia villosa - Hairy vetch
Lifecycle
• Oval shaped eggs are laid at the end of long
silken stalks. These single eggs start off green
and turn grey after a few days.
• The active larvae are grey or brownish. They are
alligator–like with well–developed legs and large
pincers with which they suck the body fluids from
prey insects such as aphids.
• Adult lacewings feed on pollen and also need
nectar or honeydew as food before laying eggs.
Habits• Adults are active fliers, particularly during the
evening and at night.
• considered an important predator of mealybugs
• feed on (among others) several species of aphids,
spider mites (especially red mites), thrips,
whiteflies, small caterpillars and beetle larvae.
• often used as a biological integrated insect control
program.
Plants that Attract Lacewings
Achillea filipendulina - Fern-
leaf yarrow
Anethum graveolens - Dill
Angelica gigas - Angelica
Anthemis tinctoria - Golden
marguerite
Atriplex canescens - Four-
wing saltbush
Callirhoe involucrata - Purple
poppy mallow
Carum Carvi - Caraway
Coriandrum sativum - Coriander
Cosmos bipinnatus - Cosmos
white sensation
Daucus Carota - Queen Anne's
lace
Foeniculum vulgare - Fennel
Helianthus maximilianii - Prairie
sunflower
Tanacetum vulgare - Tansy
Taraxacum officinale - Dandelion
Wasps
• many Small Wasps are important parasites of otherinsects. Adult parasites range in size from very small.
• range in size from 2 to 15 mm
• Larvae of most parasites develop inside the bodies oftheir prey, but some feed externally or pupate outsidethe host's body. These parasites are important insuppressing populations of many insects. They areimportant for control of loopers, cutworms, andaphids.
Common Pests
Spider mites
Aphids
Mealy bugs
Thrips
Cabbage Looper
Potato Beetle
Tomato Horn Worm
Squash Vine
Borer
Pest infestations
• Incidence
• Severity
Incidence
• The incidence of the pest (or damage
symptoms) is generally the proportion
of plants in a sample which are host
to the pest (or which show damage
symptoms), and is usually expressed
as a percentage.
Severity
• The severity of the infestation is a
measure of the size of the pest
population on the plants, or the extent
of the damage done, and is often
measured as so many insects per
plant, per bush, per 10 leaves, egg
masses per plant, etc.
Plant population assessment
• the three most widely used methods
employ between 4 (Raunkiaer, 1934),
6 (Braun-Blanquet, 1927) and 11
(Domin) abundance categories.
• categories of abundance are;
Economic threshold limits
(ETL)
ETL = cost of control ($/ha)
[commodity value ($/kg) x damage coefficient (kg/ha/#pest/ha)
Damage assessment
• extent of crop damage is usually
proportional to the numbers of insects
present:
*detectable but not of any economic importance.
Damage assessment
• With simple damage, such as leaf lamina being
eaten or apples infested with Codling Moth larvae,
damage can be expressed easily as proportion of
lamina destroyed or percentage of fruits infested
per tree. In some systems numbers of pests
present are correlated empirically against
expected loss of yield (percentage), on a scale of
no loss (0%) to total loss (100%)
Plant age/stage of development
• termed crop vulnerability.
• Many crops are only vulnerable to
certain pests at a particular time in
their growth (development).
Plant age/stage of development
• Generally the two most stressful
times for plants are the time of
establishment and the time of
flowering/fruit development, and at
these vulnerable times pest damage
is often most serious.
Oil palm- economic threshold
Symptoms:Soft-bodied insects covered by
shells or scales
Plant pest - Leaves
Symptoms:Twisting white or brown lines or
mines causing brown, dried-up blotches in
the leaves
Leaf miners
Plant pest - Leaves
Symptoms: Abnormal growths or galls on
buds
Gall midges, gall mites
Flowers and buds - Pest
Gall mites
• Symptoms: Rhizome bored
Banana Weevil (Cosmopolites sordidus)
Fruits - Pest
• Symptoms: Larvae in fruits
• Potential pest: Oriental Fruit Fly
Fruits - Pest
Symptoms: Small brownish-black shells
attached to the stems, sometimes with sticky
foliage
Scale insects
Trunks, branches, and stems
- Pest
Roots, bulbs, and tubers-
Pest
• Symptoms:Small holes in tubers,
onion bulbs, or other root vegetables
Slugs, wireworms
Damage to stored products
• On-farm storage is usually practised
for a while after harvest, particularly
on smaller farms, although this is
more typical of the tropical parts of
the world.
Types of pests
• Primary pests
• Secondary pests
• Fungus feeders
• Scavengers
Primary pests
• These insects are able to penetrate
the intact test of grains and seeds,
and include Trogoderma, Sitophilus,
Rhizopertha, Cryptolestes and
Ephestia spp.
Secondary pests:
• These are only able to feed on grains
already damaged by either primary
pests or physically damaged during
harvest; such as Oryzaephilus spp.
Fungus feeders
• A number of insects that are regularly
found in infested stored products are
actually feeding on the fungi growing
on the moist produce; but a few
species may be both fungus feeders
and secondary pests, such as some
Psocoptera.
Scavengers:
• These are polyphagous, often
omnivorous, casual or visiting pests
(as distinct from the resident or
permanent pests), such as
cockroaches, crickets, some beetles,
ants...
Types of damage
• Direct damage
• Selective eating
• Heating of bulk grain
• Webbing by moth larvae
• Contamination
Direct damage:
• direct weight loss or reduction in
volume.
• But this is not accurate as there is an
accumulation of frass, faecal matter,
dead bodies, etc.
Direct damage:
• All the insects and the rodents are
responsible for such damage.
• In some flour mite infestations
observed the final bulk of exuviae,
faeces and dried dead bodies
amounted to nearly 50% of the
original food volume
Selective eating:
• Some insects show preference for the
germ region of seeds and grains; thus
a fairly low level of damage will
severely impair germination of stored
seeds, and in food grains there will be
a serious loss of quality.
• This preference is shown by
Cryptolestes and Ephestia larvae.
Heating of bulk grain:
• Stagnant air becomes heated by
insect metabolism and ‘hot-spots’
develop.
• The moisture from the insects’ bodies
condenses on the cool grains at the
edge of the hot-spot, and the water
causes caking, leads to fungal
development, and may also cause
some grains to germinate.
Webbing by moth larvae:
• The pyralid larvae in stored products
all produce silk-webbing, which if
present in large quantities may clog
machinery and otherwise be a
nuisance.
Contamination:
Contamination:
• The presence of insects in the
produce, and dead bodies, exuviae,
frass, faeces, etc., causes a general
loss of quality and value; aesthetic
rejection of produce becomes even
more pronounced when prepacked in
transparent wrappings for
supermarket sale
How to know?
• Cross-infestation
• Regular inspection
Thank you!!!!!!!