ALS 3153 Class 18.Nematodes

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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groups and habits:

Decomposers

Predators 19%

Insect parasites 8% Animal parasites 33%

Plant parasites 7%

Others 33%

Poinar, 1983


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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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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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Tolerance Limit


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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.

Documents

ALS 3153 Class 18.Nematodes