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7/29/2019 ALS 3153 Class 18.Nematodes
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Plant-Parasitic Nematodes
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Nematodes
Unsegmented worms
Usually microscopic
Phylum Nematoda
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Nematodes Many different
groups and habits:
Decomposers
Predators
Insect parasites Animal parasites (often host-specific)
Plant parasites
Others (freshwater, marine, etc.)
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Nematodes Many different
groups and habits:
Decomposers
Predators 19%
Insect parasites 8% Animal parasites 33%
Plant parasites 7%
Others 33%
Poinar, 1983
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Nematodes Many different
groups and habits:
Decomposers
Predators
Insect parasites Animal parasites
Plant parasites
Others (freshwater, marine, etc.)
Beneficials in ag
Pests in ag
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Plant Parasitic Nematodes
Habits and Habitat
Ectoparasites = many kinds inhabit soil around
plant roots, feed on roots
Endoparasites = some kinds enter roots (bulbs,
and other below-ground plant parts) and feedinternally
Semi-endoparasites = partially enter into roots
Foliar nematodes = a few kinds enter above-ground plant tissue (leaves, seeds, stems)
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Foliar Nematode Symptoms on Hibiscus
Leaves Note restriction by leaf veins
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Symptoms many are typical of
plants with root damage:
Yield loss
Stunting
Yellowing Water deficiency and wilting
Nutrient deficiency
Some direct damage (knots on roots,misshapen potatoes, peanuts, etc.)
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Severe Stunting of Corn Plants by
Nematodes
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Galls or Knots on Root System
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Life Cycle
Rapid life cycles (30 days at summer
temp.)
Can build quickly to high numbers
Many species are good r-strategists
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Nematode Damage depends on:
Kind of nematodes present
Numbers of nematodes present
Environment Other organisms present
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Nematode Damage depends on:
Kind of nematodes present
Numbers of nematodes present
Environment Other organisms present
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Root Knot Nematodes
(Meloidogyne spp.)
Most important and damaging nematode
in southeast US and tropics
Produce typical gall or knot symptoms on
plant roots
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Root-knot
nematodes arewidespread key
pests on most
crops
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Root-Knot Nematode Life Cycle
Juvenile nematode moves freely in soil Enters root and moves to feeding site
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Root-Knot Nematode Juvenile in Root
becomes immobile at feeding site
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Root-Knot Nematode Female
Immobile nematode increases to large
size
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Root-Knot Female (with many eggs)
breaks through root surface;
Eggs and juveniles continue cycle in soil
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Root-knot
nematodesfemales cause
the galls seen
on roots
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Some Other Important Nematodes
Soybean Cyst Nematode in midwest US Burrowing Nematode on bananas in tropics
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Nematode Damage depends on:
Kind of nematodes present
Numbers of nematodes present
Environment Other organisms present
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Numbers of nematodes present
Tolerance Limit
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Nematode Damage depends on:
Kind of nematodes present
Numbers of nematodes present
Environment (temp., moisture, heat units,soil type, etc.)
Other organisms present (wounding of
roots can lead to possible interactions with
plant diseases)
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Nematode
Management
Except for root-knot,
usually need soilsample to confirm
that nematodes are
present
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Nematode Management
Soilborne pest, usually site specific
Nematodes dont migrate freely like
insects Hard to get to new sites
Once present, always present
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Nematode Management
Management is often before planting
Populations build up rapidly on susceptible
crops
Usually cant react to populations on
established crops, as with insects
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Sanitation = avoid introducing pests
to new locations
Clean soil
Clean planting material
Clean equipment Destroy/remove residues of infected plants
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Sanitation
Nematodes move easily on infected plantingmaterial
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Host Plant Resistance
Very important since some crops and
cultivars are poor hosts
Resistance = low nematode reproduction
on the plant
Tolerance = plant withstands nematode
damage
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Nematicides
Fumigants or nonfumigants
Some fumigants are multipurpose =
affect insects, weeds, fungi as well
+ + Effective and consistent
- - Can easily enter soil (and water)
environment (targets are soil pests)
- - Methyl bromide enters atmosphere
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Crop Rotation
Reduces populations in a site by growing
a poor or non host
Doesnt eliminate nematodes (low
numbers may persist for several years)
Objective is to lower numbers enough so
that next susceptible crop is successful
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Vetch Cover Crop with Weed Hosts
Weeds can carry nematodes through croprotations
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Fallow
Clean, weed-free fallow is a possible
rotation
+ + Starves nematodes, if 100% free of
weeds
- - Serious problems with soil erosion,
runoff, etc.
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Heat
Pasteurization or steaming of soil
Solarization
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Biological Control
Few successful examples ofintroduced
control (difficult to introduce organisms
into soil environment)
Natural biological control agents present
in most soils
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Pasteuria on Sting Nematode Common bacterial parasite that attacks
nematodes
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Nematode-trapping Fungi
Dactylar ia brochopaga
Arthrobo trys ol igospora
Experiment I
Adhesive knobs
Potential in Biocontrol
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Organic Amendments
Decomposition products may affect some
nematodes
Improve environment for biological control
Amendments can benefit plant health
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Organic Amendments
Decomposition products may affect some
nematodes
Improve environment for biological control
Amendments can benefit plant health
Amendments can benefit plant whether
nematodes are present or not --- they
contain N and other plant nutrients !
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Nematode Management other
methods:
Improved plant health by adding water,
fertilizer, amendments, mulch, etc.
Manipulate planting dates
Remove weed hosts
Etc
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Nematode Management = No
Quick Answers
Cant eliminate nematodes
No nematicides available for many
crops
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References
Text, pp. 196-201.
Andrews, J.H., and I. Tommerup. 1995.
Advances in Plant Pathology. Vol. 11. Academic
Press, San Diego. Ch. 8. Barker, K.R. et al. 1998. Plant and Nematode
Interactions. American Society of Agronomy,
Madison, WI.
Poinar, G.O. 1983. The Natural History of
Nematodes. Prentice-Hall, Englewood Cliffs, NJ.