1. Introduction to Plant Parasitic Nematodes and Their Management
Jimmy R. Rich and Stanley B. Hendley
IFAS/NFREC
University of Florida

2. Nematodes Human Parasitic Insect Parasitic Plant Parasitic
Phylum Nematoda
Roundworms
Microbial Feeders
(90% plus)
Animal Parasitic
Human Parasitic
Insect Parasitic
Plant Parasitic
Nematodes – Nematodes are small, mostly microscopic, nonsegemented roundworms. However, sizes range widely, and animal parasitic nematodes are generally largest. The vast majority of nematodes are beneficial microbial feeders and reside in the soil. They help promote healthy soil environments, that includes nutrient recycling. Other nematodes, such as insect feeders, provide benefits through reduction in populations of insects, e.g. mosquitoes, that are harmful to plants, animals and man. (The drawing shows the morphology of a typical plant-parasitic nematode. Note that some nematodes swell and are not vermiform (wormlike) during parts of their life cycle. This drawing is of a ‘ring’ nematode, it is widely found and quite damaging in golf courses and home lawns.

3. Interesting Facts Most numerous animal Second most numerous species
Size: mostly microscopic
Longest is 26 feet (in Blue whale)
Simple morphology
No circulatory system
No respiratory system
No skeleton
Interesting Facts – Nematodes are estimated to be the most numerous animals in the world, even more than insects. To paraphrase one eminent nematologist, he said ‘should everything else on earth disappear except nematodes, their would still be a dim outline of all that had been present. (Note the scanning electron micrographs of, in this case, a plant-parasitic nematode – 1. Upper right, the cuticle (skin) of a nematode with the typical lateral line and annules (rings) on the body; 2. A male nematode tail with reproduction organs – spicules; 3. Face view showing the opening where the stylet (spear) protrudes for plant feeding).

4. Examples of Non-Plant-Parasitic Nematodes
Animal Parasites
Canine heart worms,
Ascaris
Human Parasites
pinworms,
hookworms
Insect Parasites
mosquitoes, mole
crickets, citrus weevils
Examples – Most people can relate to nematodes found in their pets and those sometimes found in humans. However, these are seldom called ‘nematodes’ but rather ‘parasites, helminthes, roundworms, etc. Dog heartworms, for example, are nematodes and transmitted by mosquitoes. Human nematode parasites affect upwards of ½ billion people worldwide. Some insect parasitic nematodes are now commercially available and provide safe and effective control of insects. The photo at the upper right shows nematodes infecting grasshoppers – the nematodes can be seen with the naked eye and appear as ‘strings’. Below are mosquito larvae infected with nematodes.

5. Plant-Parasitic Nematodes
Over 6000 known species
Present in all ecological niches
Attacks almost all plants
Cause 10% losses to crops
Reduces ornamental growth
Serious turf problems
Big problem on tree crops
Plant Nematodes – The study of plant-parasitic nematodes is relatively young compared to study of plant diseases and insects. Thus, there is still very much to be learned. However, we know that nematodes parasitize a huge number of plants (if not all) and cause billions of dollars worth of damage to world food crops as well as tree crops, turf and ornamentals. Damage or potential damage from nematodes must always be considered when producing plants. (The photos show palm trees declining with eventual death from the ‘red ring’ nematode disease. The nematodes are transmitted by the palm weevil.

6. Morphology A nematode has: Digestive organs Reproductive organs
Excretory structures
Muscles
Nerves
Tough skin or “Cuticle”
Morphology – Nematodes have a more detail structure than shown here. However as indicated, they possess no circulatory, respiratory or skeletal systems. Body ‘structure’ is maintained by fluid that surrounds the organs in the body cavity (pseudocoelom). As a result of no skeletal structure, nematodes must always be surrounded in a film of water or other liquid to prevent body collapse from drying and resultant death. Hence, do not allow nematode soil samples to dry out!

7. Plant-parasitic nematodes all have
stylets (spears) that penetrate cells
and withdraw the contents.
Stylet – Plant-parasites possess a stylet (spear) which differentiates them from other groups of nematodes. The stylet is used to puncture plant cell walls and membranes to allow withdrawal of cell contents. Stylets of most plant nematodes are hollow which provides a channel for cell contents to pass. A few have solid stylets that contain groves on the outside for this purpose. The general feeding process is: 1) the stylet pierces a cell; 2) digestive glands (esophageal glands) discharge enzymes which partially dissolve cell contents; then 3) contents are sucked by the action of the pumping bulb (median bulb) into the intestines (no stomach).

8. Nematode Names
Plant nematodes have both common and scientific names, some of economical importance, by common name, are:
Root-knot, Sting, Stubby-root, Reniform, Lance, Ring, Lesion, Burrowing, Citrus,
Spiral, and Cyst
Nematode Names – Plant nematodes are generally given common names according to either damage symptoms they produce on plants or some striking morphological feature they possess. For example, root-knot nematodes produce root ‘knots’ while stubby root nematodes cause ‘stubby’ looking roots. The cuticle of ring nematodes looks like a stack of coins giving it a ‘ringed’ appearance, while lance nematodes have a robust stylet, resembling a ‘lance’.

9. Feeding Habits Nematodes may be grouped by feeding habit as:
Endoparasitic– entire body inside the root
Ectoparasitic– entire body outside the root
Semi-endoparasitic- part of body inside root
By movement when feeding, they are called:
Sedentary – mostly immobile during their life
Migratory – mobile for all their life.
Feeding Habits. Nematode feeding habits are described according to whether they feed inside or outside a root and if they move or not while feeding.

10. Feeding Habits of Some Plant-parasitic Nematodes
Root-knot
Feeding Habits –Root-knot nematodes are sedentary and endoparasitic while the lesion nematode is migratory and endoparasitic. Note that the root-knot nematodes swell and appear pear-shaped, and thus, become sedentary.
Lesion

11. Feeding Habits of Some Plant-parasitic Nematodes
Cyst
Ring
Feeding Habits – Cyst nematodes are sedentary and semi-endoparasitic while ring nematodes are sedentary and ectoparasitic.

12. Feeding Habits of Some Plant-parasitic Nematodes
Stubby root
Feeding Habits – The stubby-root nematode is migratory and ectoparasitic while reniform nematodes are sedentary and semi-endoparasitic. Most nematodes initiate feeding just behind tips of young roots. However, some like the stubby-root nematode feed directly on the root tip, generally preventing further root elongation – hence stubby roots.
Reniform

13. Nematode Damage
Nematodes damage plants by reducing or modifying root mass
Root cells are killed or modified to serve as food for the nematode
Typical root and foliar symptoms result
Nematode Damage – Nematode damage is mainly a function of reduction of plant root mass. The feeding activities of most plant nematode result in plant root destruction, thereby limiting water and nutrient uptake by the plant. However, some nematodes cause the production of giant or nurse cells whose sole purpose is to feed the nematode (for example, root-knot nematodes). These nematodes not only physically damage a root from their activities but also redirect plant food for themselves.

14. Foliar Damage Symptoms
Water and Nutrient Stress –
Premature Wilting
Leaf Yellowing (Chlorosis)
Plant Stunting
Irregular Symptom Patterns
Foliar Symptoms - Damage from nematodes in plant foliage may be manifest directly from feeding activity on leaves, flowers and stems. Foliar feeding nematodes, however, are much less prevalent than those feeding on roots. Root feeding nematodes produce foliar symptoms that mirror root damage. In fact, most foliar-induced symptoms are the same as those plants show when not receiving sufficient water and nutrients – wilting, yellowing, and stunting. As a result, nematode problems are often misdiagnosed and blamed on a lack of fertilizer and water.

15. Foliar Symptoms- Aerial View
Aerial Photo -The sugarbeet field is almost entirely affected by sugar beet cyst nematodes. The field shown at the top was treated with a chemical (called nematicide) to reduce damage from the cyst nematodes. Note the dark green nematicide-treated strips in the field at the bottom of the photo.

16. Foliar Symptoms – Oval Pattern
Damage Patterns – Unlike the previous slide, most nematode damage will result in stunted, yellowing or both symptoms on plants. Areas of damage in a field are spotty across a field and irregular, usually oval, in shape. Nematodes almost never produce ‘row’ patterns.

17. Foliar Symptoms- Plant Death
Plant Death – These grape tomatoes are in the last stages of decline/death due to root-knot nematodes. Nematodes do not usually kill plants outright but rather lead to a slow decline sometimes leading to death.

18. Foliar Symptoms- Stunting
Stunting – Cabbage plants in rows shown in this slide are the same age and planted on the same day. A nematicide was used to kill ‘sting’ nematodes before planting the cabbage on the left.

19. Foliar Symptoms- Leaf Yellowing

20. Foliar Symptoms- Stunting
Stunting – The cabbage plant on the left simply looks young, not necessarily nematode damaged. However, it is greatly stunted compared to the same age plant on the right.

21. Foliar Symptoms- Slow Decline
Slow Decline – Florida citrus is greatly affected by three different nematodes – ‘citrus, burrowing, and lesion’. Burrowing nematode damage shown here results in citrus ‘slow decline’ disease, note spare vegetation on tree in the foreground. Trees gradually produce less fruit, leaves and new growth. Whole orchards have been destroyed by this nematode

22. Foliar Symptoms- Toppling
Toppling Disease – ‘Burrowing’ nematodes cause damage to banana roots and banana yield is affected. However, the major problem caused by nematodes on this plant is ‘toppling’. Banana roots are so severely affected that they cannot hold the tree upright once the extra weight of the developing fruit is added.

23. Root Damage Symptoms Galled Roots Stunted Roots Swollen Root Tips
Root Lesions
Increase in Lateral Roots
Root Damage Symptoms – Nematode damage on roots is only readily diagnosed in a few cases. For example, presence of root swellings or galls would usually indicate that root-knot nematodes are present. Also, plant root systems that show stubby and swollen root tips are typical of sting and stubby root nematode damage. However, most nematode damage simply results in stunted root systems or roots that show areas of dead tissue (lesions). These symptoms could be caused by a variety of other causal agents. For accurate problem determination, nematodes must be extracted and identified in a laboratory.
Slide 22. Root Damage Symptoms – Nematode damage on roots is only readily diagnosed in a few cases. For example, presence of root swellings or galls would usually indicate that root-knot nematodes are present. Also, plant root systems that show stubby and swollen root tips are typical of sting and stubby root nematode damage. However, most nematode damage simply results in stunted root systems or roots that show areas of dead tissue (lesions). These symptoms could be caused by a variety of other causal agents. For accurate problem determination, nematodes must be extracted and identified in a laboratory.
Slide 23. Root Galling – Root-knot nematodes are widely distributed and major soil pests worldwide. These nematodes cause plant cells to multiply rapid producing ‘knot’ (galls) on roots. Females are imbedded inside these galls. As indicated, root galling is easily observed and quite diagnostic for presence of these nematodes.

24. Root Symptoms- Galling
Root Galling – Root-knot nematodes are widely distributed and major soil pests worldwide. These nematodes cause plant cells to multiply rapidly producing ‘knots’ (galls) on roots. Females are imbedded inside these galls. As indicated, root galling is easily observed and quite diagnostic for presence of these nematodes.

25. Root Symptoms- Cyst Nematodes on Roots
Cysts on Roots – Cyst nematodes do not cause major malformations or lesions on roots. However, their swollen bodies are on the outside the root. By careful examination with a magnifying glass, ‘pearly’ white cysts on the roots can be seen.

26. Root Symptoms- Peanut Pod Galling
The peanut root-knot nematode is the most damaging nematode pest on the peanut crop. The nematode affects peanuts in a number of ways including reducing plant growth, hence pod development. Additionally however, the nematode may cause pod abortion, weaken pegs so that they remain in the ground, open wounds for rot organisms, and generally reduce nut quality.

27. Root Symptoms- Lesions
Root Lesion - Root lesions may be caused by any number of factors. Among these are nematodes, primarily lesion and burrowing, that produce dead areas on roots. For accurate diagnosis, however, soil and root samples must be analyzed in a laboratory.

28. Root Symptoms – Sweet Potatoes
Sweet Potatoes - Nematodes not only damage roots, thus affecting plant growth, but also other plant parts present in soil. Root and tuber crops are affected in appearance and quality as well as quantity produced. Pictured here are sweet potatoes infected with root-knot nematodes resulting in a serious reduction in both appearance and quality.

29. Root Symptoms - Irish Potatoes
Irish Potatoes - Root-knot nematode damage in Irish potatoes is a major problem in production of this crop. The stained dark red spots pictured here are females of the root-knot nematodes. Potatoes affected by nematodes will rot in storage.

30. Root Symptoms- Potato Rot Nematode
Potato Rot - The ‘potato rot’ nematode causes accelerated tuber rotting as shown in this photograph. Tubers infected with these nematodes are a total loss

31. Root Symptoms- Sprangling
Root Sprangling - Nematodes are a major problem on some root crops, reducing yield and resulting in rotting but sometimes more importantly, growth distortion. For example, even low populations of nematodes can cause root ‘sprangling’ on crops such as carrots and turnips, thus rendering them unmarketable.

32. Disease Interactions
Nematodes cause plant disease and can make fungal and bacterial diseases worse.
Disease Interactions - Nematodes not only cause plant disease by themselves but also increase plant damage caused by other disease-causing organisms such as bacteria and fungi. For example, the presence of nematodes provides entry points for invasion of Fusarium wilt fungi in a number of crops. (Note in the photograph that presence of the Fusarium wilt fungus showed little affect on plant growth, but damage dramatically increased in the presence of root-knot nematodes (Mi, Mh, and Mj).
Control Fusarium(F) Mi +(F) Mh +(F) Mj +(F)
An example is Fusarium wilt where root-knot
nematodes create entry points for the fungus.

33. Problem Identification
Combinations of:
Foliar Symptoms
Roots Symptoms
Cropping History
Laboratory Analysis
Problem Identification – To identify a nematode problem, one must consider individual plant foliar and root symptoms, field damage patterns, plus have an idea of cropping history (were susceptible crops previously grown?). If nematodes are suspected, a final laboratory analysis is often needed to confirm suspicions.

34. Sampling Basics County Agents have kits available
Sample 10”-12” deep; in turf 4”-6”
Sample only in moist soils – Not dry or wet
Use a plastic bag only
Do not let the sample get too hot or cold
Send 1 pint of soil and 1 cup of roots
Send for extraction ASAP
Do not allow samples to become hot or frozen, either way nematodes will be killed
Sampling – Proper sampling and handling of nematode samples are a must or laboratory analyses will not provide accurate results. Carefully follow the dos and don’ts listed on the slide for accurate laboratory results. Remember, nematodes are living animals and will die/disappear from samples if not handled properly.

35. Management Methods Exclusion Sanitation Rotation Plant Resistance
Fallow
Solarization
Nematicides
Management - Methods for nematode management are generally broken down into: 1) exclusion, 2) sanitation, 3) cultural practices, 4) plant resistance, and 5) nematicides. The heading, cultural practices, is not listed in the slide. Rather, those cultural practices of rotation, solarization, and fallow are listed separately. This was done to emphasize the importance of these techniques, particularly where use of nematicides are prohibited or not available.

36. Exclusion/Sanitation
Buy or grow transplants that are nematode-free.
Use nematode-free soil or potting medium
Clean tools and equipment when changing areas or fields
Remove infected plant roots
Exclusion/Sanitation – Keep pests out!! For example, buy or grow transplants that are nematode-free. The soil medium is obviously the greatest consideration here and it should be nematode-free. Remove potentially contaminated soil and plant materials from tools and other equipment when moving from one area or field to another. For nematodes, this is usually just a matter of rinsing tools thoroughly with water.

37. Rotation Move garden to a new location
Rotate grasses with broadleaf plants
Plant cover crops that are poor hosts
Keep weeds in check, many are hosts
Maintain high organic matter levels
Irrigate frequently and use higher fertilizer rates
Rotation – This ‘cultural practice’ can/should be a cornerstone of any nematode management program. In most annual crops, proper crop rotation with non- or poor hosts of nematodes is the only nematode management needed. However, economics of growing ‘rotation’ crops, practicality including land requirements, and specific nematode host range many times limits rotation options. This practice should always be keep in mind, even in small garden plots, where perhaps sweet corn could be rotated with more susceptible crops such as okra.

38. Soybean Rotation
Soybean Rotation – Planting a poor or nonhost of nematodes for two years will generally reduce nematode populations and allow acceptable plant growth of a susceptible crop.

39. Resistance
Resistance breeding has been mainly to root-knot nematode (Meloidogyne spp.)
Resistance, however, may be to only 1 root-knot species
Examples of resistance can be found in tomato, snap bean and some southern peas
Little resistance is available to other nematode species
Resistance - The use of plant resistance, when available, should always be encouraged. Resistance to root-knot nematodes is available in crops such tomato, soybean, snap bean, southern peas and several other crops. A word of caution, do not rely solely on plant resistance since certain populations of nematodes can overcome resistance beginning either immediately or sometimes several years after regularly planting the resistant plant.

40. Resistant/Not Resistant
Resistant/Not Resistant – The process of finding, breeding and selecting plants with resistance to nematodes is long and tedious. The plant on the left shows good resistance to root-knot nematodes as evidenced by lack of galling, note the susceptible, galled root system on the right.

41. Solarization Only works moderately well with nematodes
Has added advantage of reducing weed problems
Use clear plastic, make sure soil is tilled and moist
Use in the hottest months and leave
6-8 weeks
Solarization – This practice dramatically increases soil temperatures which in turn kills many weed, fungal, insect and nematode pests. Temperatures that kill nematodes are reached only in the first six inches or so of soil leaving living nematodes present at lower depths. Thus, correct use of solarization will reduce nematode populations, but not enough to prevent all nematode damage to crop plants. It is only useful to minimize nematode damage but should be used in combination with other management practices.

42. Solarization- Laying Clear Plastic
Laying Clear Plastic – Solarization increases soil temperatures and these temperatures kill nematodes. l Soil temperatures that kill nematodes, however, are only reached to depths of 6-8 inches. Remaining nematodes below this depth are usually present in high enough numbers to still cause plant damage.

43. Successful Nematode Control
Management Summary
No single practice will control nematodes, so two or more control methods must be used.
Sanitation
Successful Nematode Control
Management Summary - At least two management practices must be used to minimize nematode damage. In addition, good crop husbandry practices such as addition of organic matter, good soil fertility and irrigation will also help reduce nematode damage.
Resistance
Chemicals

44. FAQ - Organic Matter
Does compost and organic matter control nematodes?
The answer is generally no, however, they increase water and nutrients available to the plant.
Thus a healthier plant can tolerate more nematode damage.

45. FAQ - Resistance
My nematode ‘resistant’ plant still had lots of nematode damage?
A resistant plant is ‘resistant’ to only a nematode to which it was bred
For example, a plant may be
resistant to only one type (species)
of nematode but not others

46. FAQ – Wet or Dry
Do nematodes cause damage under both wet and dry conditions?
Greatest damage is caused when conditions are dry.
Wet conditions mask some damage until root rotting from nematode damage begins.

47. FAQ - Nematicides
What is the best ‘nematicide’ available for nematodes?
All effective nematicides are restricted use chemicals and cannot be bought without a pesticide license
Products found in garden stores are ‘at best’ nematode suppressants.
Generally, these products are not recommended for nematode control

48. FAQ - Fallow cannot feed, they will starve, however:
Is fallow recommended for nematode management?
Fallow makes sense because, if nematodes
cannot feed, they will starve, however:
Many weeds are host to nematodes,
thus they must not be allowed to grow.
At least one growing season of fallow must be
used and fallow depletes soil organic matter
During the ‘winter’, most nematodes are
relatively dormant and do not feed anyway.

49. UF/IFAS EDIS Publications http://edis.ifas.ufl.edu/TOPIC_Nematodes
General Nematology
Nematodes in the Yard
Lawn Pest Nematodes
Landscape Nematodes
Urban Tree Pest Nematodes
Vegetable Nematodes
Fruit Pest Nematodes
EDIS Publications - More information on nematode biology, sampling, and management can be found on the UF/IFAS EDIS Website address listed on the slide.
EDIS also contains a large amount of information on other plant pests.

50. Authors: Jimmy Rich and Stanley Hendley; for comment or information, please contact
Photo Credits: R. P. Esser, R. S. Hussey, W. F. Mai, R. A. Motsinger, A. W. Johnson,
D. W. Dickson, A. Steele, H. L. Rhoades,
M. A. McClure, J.D. Eisenback, K. R. Barker
Entomology and Nematology Department Copyright University of Florida 2003