1. Nematode Damage
Rarely, does a single nematode pose a threat to a plant. (exceptions - virus vectors and sting nematodes)
Damage to plant parts results from many nematodes feeding at once.
The root system of plants can be growing in the presence of hundreds of thousands or even millions of nematodes.

2. Nematode Damage
Quite often it is very difficult to see symptoms caused by nematode (even though yield loss may be reduced by 30%).
This is compounded by the fact that nematodes are rarely normally distributed in a field.
Nematode damage can be confused with herbicide and other chemical injury.

3. Damage
Mechanical injury results from the nematode stylet puncturing the cell wall, and is followed by the secretion of enzymes and nutrient extraction. This process leaves cells that are damaged or completely destroyed. 
Nematode damage can result in a variety of symptoms: 
1. Lesions
2. Galls or swellings 
3. Stunted plants
4. Loss of vigor
5. Excessive root branching 
6. Twisted or distorted stems and/or leaves 
7. Disruption in flower development / sterility 
8. Dead or incapacitated root tips
Disease Complexes - While nematodes are devastating pathogens, their most significant influence in agriculture results from their participation in pathogen complexes. 

4. Damage

5. Damage

6. Nematodes as Plant Pathogens
Endoparasites
Vermiform all stages
Lesion nematode
Pine wilt nematode
Swollen females
Cyst nematodes
Root knot nematode
Ectoparasites
Dagger nematode
Management

7. ENDOPARASITES ECTOPARASITES Root-knot Root-lesion nematodes nematodes
Reniform nematodes
Dagger nematodes

8. Taxonomy Kingdom Animalia Phylum Nemata Class Secernentea
5 other orders contain free-living forms and parasites of animals
Order Aphelenchida - parasites of higher plants (usually on above ground parts), fungi, and insects
Important genera:
Aphelenchoides - foliar nematode
Bersaphelenchus - pine wilt nematode
Order Tylenchida - parasites of higher plants, insects, and fungi – largest % of plant pathogens
Heterodera spp. - cyst nematodes
Meloidogyne spp. - root-knot nematodes
Pratylenchus spp. - root-lesion nematodes

9. Taxonomy Kingdom Animalia Phylum Nemata
Class Adenophorea (as opposed to Secernentea)
11 other orders contain free-living forms and parasites of animals and microorganisms
Order Dorylaimida - plant parasites/virus vectors
(Stylet without knobs and no distinct median bulb)
Important genera:
Xiphinema spp.- dagger nematode Longidorus spp.- needle nematode Trichodorus spp.- stubby-root nematode

10. Root lesion nematodes Pratylenchus spp.
7 important species in United States
Most plants are susceptible to one or more species
Migratory endoparasite, can leave and reenter the roots many times in its lifecycle.
Males may or may not participate in reproduction.

11. Root lesion nematodes

12. Pine wilt nematode Bursaphelenchus xylophilus
Hosts - Scots, Austrian, jack, mugo, and red pines and, less commonly, white pines
Interaction between a nematode, insect, sometimes fungi

13. Attacks Pines at Any Age

14. Few vs. the Many

15. Disease Cycle

16. Vector on Healthy Plant

17. Nematodes in the Trachea of Vector

18. Cyst nematodes Heterodera spp. H. schactii – sugar beet cyst nematode
H. glycines – soybean cyst nematode – $3 billion in damage/year
All are sedentary, endoparasites
After J2 stage enters the root and establishes a smaller feeding site than root-knot nematode. No gall production.
After the J2 becomes an adult, males leave the root to fertilize the females that have protruded through the root.
The female will swell upon maturity producing several hundred eggs outside and inside of her body. When she dies (4 wks old) her body will become a protective cyst for her young.
Some eggs will hatch immediately, some later in the season, next year or years, or never.

19. Soybean cyst nematode

20. Soybean cyst nematode disease cycle

21. Soybean cyst nematode No visible symptoms with 30% yield loss

22. Root-knot nematode Meloidogyne spp. M. incognita – southern-root knot
M. hapla – northern root-knot
All are sedentary, endoparasites
After J2 stage enters the root and establishes giant cells (cells enlarge and rapidly divide) creating a more efficient nutrient sink for the nematode = gall production.
After the J2 becomes an adult, males leave the root. The female will swell upon maturity producing several hundred eggs. Males may or may not participate in reproduction.
Population is managed by the ratio of females : males that are produced. Immature females can change to males if the population density can not be supported.

23. Root-knot nematode Juveniles in root Male, hatching from cuticle
Gall, with female
protruding
Giant cell

24. Root-knot nematode

25. Root-knot Nematode

26. Dagger nematodes Xiphinema spp. 3 important species in United States
Characterized by long body and stylet.
Sedentary ectoparasite. Feeds only at the root tips.
Feeding produces knobby, stunted roots.
Males are required for reproduction, females produce very few eggs, but lives several months (most other nematodes live a few weeks).

27. Dagger nematodes

28. Dagger nematodes
Stubby roots
Carmi, IL
Stunted plants
Carmi, IL

29. Dagger nematodes (grape fan leaf virus)

30. Management Strategies
I. Cultural practices - Includes agricultural tactics that indirectly influence pathogen populations and communities.
a. Crop rotation
b. Trap crops
c. Fallow
e. Flooding or heat
f. Tillage
g. Planting date  

31. Management Strategies
II. Breeding for resistance
The use of nematode resistant varieties is a major management strategy.  In many crops, chemical control is not economically viable and breeding is the only available tactic.   
One of many limitations is that where races of nematodes are problematic (such as soybean cyst nematode and root-knot nematode), effective control of nematode populations occurs only when the plant contains resistant genes against the specific race present.

32. Management Strategies
III. Biocontrol
The use of fungi, bacteria, viruses, other nematodes,to manage nematodes.  The are many examples of biocontrol of nematodes, however, very few work in the field.
Bacterium - endospore forming Pasteuria penetrans
Fungus - adhesive rings by Arthrobotrys spp.

33. Management Strategies
IV. Chemical control
The use of pesticides or other chemicals to reduce or eliminate nematode populations.
Nematicides - are used to manage nematode populations on high value crops.  The use of nematicides is being reduced because of toxicity to the environment and to humans.
examples – Methyl Bromide, Vapam, Telone, Temik, Mocap, Counter