PlantParasitic Nematodes

1
Plant-Parasitic Nematodes
2
Nematodes

• Unsegmented worms
• Usually microscopic
• Phylum Nematoda

3
Nematodes Many different groups and habits

• Decomposers
• Predators
• Insect parasites
• Animal parasites (often host-specific)
• Plant parasites
• Others (freshwater, marine, etc.)

4
Nematodes Many different groups and habits

• Decomposers
• Predators 19
• Insect parasites 8
• Animal parasites 33
• Plant parasites 7
• Others 33

Poinar, 1983
5
Nematodes Many different groups and habits

• Decomposers
• Predators
• Insect parasites
• Animal parasites
• Plant parasites
• Others (freshwater, marine, etc.)

Beneficials in ag
Pests in ag
6
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 feed
  internally
• Semi-endoparasites partially enter into roots
• Foliar nematodes a few kinds enter above-ground
  plant tissue (leaves, seeds, stems)

7
Foliar Nematode Symptoms on Hibiscus Leaves
Note restriction by leaf veins
8
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.)

9
Severe Stunting of Corn Plants by Nematodes
10
Galls or Knots on Root System
11
Life Cycle

• Rapid life cycles (30 days at summer temp.)
• Can build quickly to high numbers
• Many species are good r-strategists

12
Nematode Damage depends on

• Kind of nematodes present
• Numbers of nematodes present
• Environment
• Other organisms present

13
Nematode Damage depends on

• Kind of nematodes present
• Numbers of nematodes present
• Environment
• Other organisms present

14
Root Knot Nematodes(Meloidogyne spp.)

• Most important and damaging nematode in southeast
  US and tropics
• Produce typical gall or knot symptoms on plant
  roots

15
Root-knot nematodes are widespread key pests
on most crops
16
Root-Knot Nematode Life Cycle

• Juvenile nematode moves freely in soil
• Enters root and moves to feeding site

17
Root-Knot Nematode Juvenile in Root becomes
immobile at feeding site
18
Root-Knot Nematode Female

• Immobile nematode increases to large size

19
Root-Knot Female (with many eggs) breaks through
root surfaceEggs and juveniles continue cycle
in soil
20
Root-knot nematodes females cause the galls seen
on roots
21
Some Other Important Nematodes

• Soybean Cyst Nematode in midwest US
• Burrowing Nematode on bananas in tropics

22
Nematode Damage depends on

• Kind of nematodes present
• Numbers of nematodes present
• Environment
• Other organisms present

23
Numbers of nematodes present
Tolerance Limit
24
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)

25
Nematode Management

• Except for root-knot, usually need soil sample to
  confirm that nematodes are present

26
Nematode Management

• Soilborne pest, usually site specific
• Nematodes dont migrate freely like insects
• Hard to get to new sites
• Once present, always present

27
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

28
Sanitation avoid introducing pests to new
locations

• Clean soil
• Clean planting material
• Clean equipment
• Destroy/remove residues of infected plants

29
Sanitation

• Nematodes move easily on infected planting
  material

30
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

31
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

32
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

33
Vetch Cover Crop with Weed Hosts

• Weeds can carry nematodes through crop rotations

34
Fallow

• Clean, weed-free fallow is a possible rotation
• Starves nematodes, if 100 free of weeds
• - - Serious problems with soil erosion, runoff,
  etc.

35
Heat

• Pasteurization or steaming of soil
• Solarization

36
Biological Control

• Few successful examples of introduced control
  (difficult to introduce organisms into soil
  environment)
• Natural biological control agents present in most
  soils

37
Pasteuria on Sting Nematode

• Common bacterial parasite that attacks nematodes

38
Nematode-trapping Fungi
Experiment I
Adhesive knobs
Dactylaria brochopaga
Potential in Biocontrol
Arthrobotrys oligospora
39
Organic Amendments

• Decomposition products may affect some nematodes
• Improve environment for biological control
• Amendments can benefit plant health

40
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 !

41
Nematode Management other methods

• Improved plant health by adding water,
  fertilizer, amendments, mulch, etc.
• Manipulate planting dates
• Remove weed hosts
• Etc

42
Nematode Management No Quick Answers

• Cant eliminate nematodes
• No nematicides available for many crops

43
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.