DISEASES OF ROOTS MIGRATORY ECTOPARASITES

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
-Most common type of plant parasitic nematode
-Life cycles simple and similar
-Most genera have many species
-Most have wide host ranges
-Pathology similar but severity and thresholds vary
-Nematicides primary control measure, if available

MIGRATORY ECTOPARASITES
LIFE CYCLE

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Dolichodoridae
Dolichodorus = “awl” nematodes, 16 species
Based on shape of stylet

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Dolichodoridae
Belonolaimus = 10 species
Belonolaimus longicaudatus = “sting” nematode

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Agrios

Belonolaimus
Female Tail
Dolichodorus
Female Tail
Belonolaimus
Male Tail
Dolichodorus
Male Tail

Belonolaimus longicaudatus = sting nematode
Life cycle and biology
- The most damaging migratory ectoparasite.
- Very serious on a wide variety of crops in the
southeastern US = corn and many other vegetables,
cotton, peanuts, soybean, turf and pasture grasses,
forest trees.
- Most prominent in warm sandy (80%) soils where
they can completely destroy a crop.
- Life cycle is about 4 weeks.

Belonolaimus longicaudatus = sting nematode
Stylet thrusts deep
into roots
= local lesions
Soybean
Stubby or coarse roots
may be present
L.I. Miller
Nemapix 1

Belonolaimus longicaudatus = sting nematode
-Feed on root tips or
on sides of root.
-Feeding on one side
stops growth, other side
continues to grow
so root curves.
Soybean
L.I. Miller
Nemapix 1

Belonolaimus longicaudatus = sting nematode
Plants wilt, appear chlorotic and are reduced in size.
In severe infestations the entire crop may die.
L.I. Miller
Nemapix 1

Belonolaimus longicaudatus = sting nematode
Symptoms
- Root system is greatly reduced,
- Increase in lateral root production = "blind root tip"
- Secondary invasion my other bacteria and fungi
Interacts with Fusarium on cotton.
- Water and nutrient uptake are greatly reduced.

Belonolaimus longicaudatus = sting nematode
Control
Physical incorporation of nonfumigant granular
nematicides (aldicarb, carbofuran, dasanit).
Soil fumigation
Up to 500% yield
increases have been
reported when
controlled.
Cabbage
SON
Nemapix 1

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Dolichodoridae
Tylenchorhynchus = “stunt” nematodes, 130+ species
Several morphologically similar genera, 250+ species

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Agrios

Tylenchorhynchus sp.
U. Zunke
Nemapix 2

Tylenchorhynchus = stunt nematode
Life cycle and biology
-Common on roots of many plants.
-Feed on epidermal cells in the region of root elongation
and region of root hairs
- Rarely important unless in very high numbers
such as tobacco, turf grasses, pastures, corn.
- Common in grassland and rangeland.
- Can be serious on azaleas, African violet, pines
Symptoms
Large numbers debilitate roots, tops become stunted and
chlorotic, and yield may be reduced
Control
Nematicides

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Hoplolaimidae
Hoplolaimus = “lance” nematodes, 30+ species

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Agrios

Hoplolaimus
1-2 mm in length

Hoplolaimus = “lance” nematodes
Life cycle and biology
-Usually ectoparasites but sometimes may be found
partly or entirely within root tissues
= semi-endoparasite -> endoparasite.
- May be ectoparasite on young roots and endoparasite
on older roots.
- Life cycle can be 6-7 weeks.
- In high populations may damage many different crops;
grasses, cotton, pine, oak, wheat, banana, sugarcane,
corn, soybean, coffee, tea, turf and forest trees.

Hoplolaimus = “lance” nematodes
Life cycle and biology
- Nematode kills cells of cortex or of the vascular tissue
=> extreme necrotic lesions extending to cells some
distance beyond those directly adjacent to the parasite.
Extensive invasion results in destruction of large areas
of root including phloem and xylem tissues.
Can impede mycorrhizal associations of pine trees,
which are essential for the normal growth of trees.

Hoplolaimus = “lance” nematodes
Symptoms
- Stunting, chlorosis, wilting, yield reduction.
- Yellow, red or brown necrotic areas on root
=> depends on density and/or the duration of feeding.
- Holes in cortex

Stunting and chlorosis of soybean caused by lance
nematode, Hoplolaimus columbus
S. Koenning
Nemapix 2

Hoplolaimus = “lance” nematodes
Control
- Soil fumigation
- Nematicides
- Dips for sprigs of Bermuda grass.
- Fallowing may help but H. columbus survived storage
in dry soil for 5 years.

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Hoplolaimidae
“Spiral Nematodes”
Scutellonema spp.
Rotylenchus spp. – 80+ species
Helicotylenchus spp. – 160+ species

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Agrios

Scutellonema
Life cycle and biology
- Feed as ectoparasites on roots of cotton, coconut,
banana, corn, ornamentals, peanut.
- S. bradys = “yam nematode”
- In tuber crops (yams) and bulbs (lilies) also feeds as a
migratory endoparasite.
- Large populations can develop during storage 6000/g!

Scutellonema
Symptoms
- Causes lesions in superficial tissues under tuber skin.
Turn yellow – brown – black.
- In stored tubers, may cause dry rot if bacteria are not
present or wet rot if bacteria are present.
Fusarium may also be present.
Can lead to complete tuber destruction.
Control
Yams = plant nematode-free tubers,
Hot water treatment or soaking seed in nematicides.
Field application of nematicides.

Scutellonema bradys damage to yam
Flickr
IITA Images

Rotylenchus spp. = “spiral” nematodes
Life cycle and biology
- Migratory ectoparasite but may enter root partly or
wholly during feeding.
- Occasionally referred to as a sedentary ectoparasite or an
ecto-endoparasite but does not stay permanently attached.
- Life cycle is about 100 days at 23 C on ryegrass.
- Reach high levels in sandy soils.
- Important on vegetables, lilies, grasses, ornamentals,
shrubs and trees, especially boxwood.
- 6/g soil can damage carrots (= 1,500/250 g soil).
- 0.5/g soil can cause root rot of lilies (= 125/250 g soil).

Rotylenchus spp. = “spiral” nematodes
Symptoms
- Lesions result from death of cells during feeding.
- Multiple attacks weaken root.
- Top growth is reduced.
- Leaves of some hosts become yellow
Control
Nematicides

Helicotylenchus spp. = “spiral” nematodes
Life cycle and biology
- Common genus with many species.
-Ectoparasites -> semi-endoparasites or ecto-endo
parasite, occasionally referred to as a migratory
endoparasite but doesn't move about actively in roots.
-Important on hardwood trees, turf, soybean, olive,
cotton, millet, tomatoes.
-Most important on banana!
H. multicinctus

Helicotylenchus sp.

Helicotylenchus spp. = “spiral” nematodes
Symptoms
-Invades cortex -> lesions developing to root rots
with other pathogens (Fusarium, Rhizoctonia).
-Since banana is propagated vegetatively, infection is
spread by planting infested rhizomes.
-Weakened root systems can cause plants to fall over
in high winds.

Helicotylenchus spp. = “spiral” nematodes
Control
- Fumigation
- Strict sanitation - rotted tissue pared away from
rhizome sets.
Sets are then treated with hot water (20 minutes at
53-55 C) and/or dipped in nematicide.
- Some genetic resistance in cotton.

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Tylenchulidae
Paratylenchus spp. = “pin” nematodes

Paratylenchus sp.

Paratylenchus sp.

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Agrios

Paratylenchus spp. = “pin” nematodes
Life cycle and biology
- Common in many native and agro-ecosystems.
- J4's lack stylet and can survive in soil for long
periods without feeding (1 year+)
- Apparently require root exudate to stimulate
final molt.
-In Oregon can damage peppermint when in high
numbers, can reach 100/g soil (=25,000/250 g soil)!
High densities in fall can contribute to winter injury.

Paratylenchus spp. = “pin” nematodes
Life cycle and biology
- Feed on epidermal cells or at base of root hair.
-May feed in one spot for long period of several
days without killing cell.
Symptoms
-However, large populations can cause brown
necrotic areas and/or kill root.

Paratylenchus spp. = “pin” nematodes
Control
- Control seldom warranted unless in very high
densities.
- Nematicides only known control.
- Appear to be more resistant to nematicides than most
nematodes.

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Criconematidae
Criconemoides spp. = “ring” nematodes
Also been known as:
Criconemella
Mesocriconema
Macroposthonia

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Agrios

Criconemoides = “ring” nematodes
Life cycle and biology
- High populations damage roots of grape, pine, elm,
maple, peach.
- Also attacks many other crops but is less serious.

Criconemoides = “ring” nematodes
Symptoms
- Necrotic lesions result from cell death.
-Destruction of new root growth affects whole plant
and its physiology.
-Contributes to "peach short life".
-Trees begin by growing normally, but die in a few
years.
-Frost damage, poor soil and other pathogens may
also be involved.
-Nematode makes trees more vulnerable to stresses.

Criconemoides = “ring” nematodes
Control
Nematicides

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Hemicycliophoridae
Hemicycliophora spp. = “sheath” nematodes

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Agrios

Hemicycliophora sp.

Hemicycliophora = “sheath” nematodes
Life cycle and biology
-Attacks some citrus, grapes, cranberry, melons,
carrots, tomatoes, pine. Up to 30% yield loss.
- Feeds as an ectoparasite on root tips.
- Hemicycliophora arenaria most important species.
- Life cycle 15-18 days at 30 C (= optimum temperature).

Hemicycliophora = “sheath” nematodes
Symptoms
- Cells may be killed at feeding site.
- Pericycle tissue is stimulated to initiate new growth
=> root tip galls due to hyperplasia and hypertrophy.
- Host shows poor growth and yield from poor root
function.
Control
- Nematicides
- Hot water dips of root stock of woody plants
For example: citrus = 10 minutes at 46 C.

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS ENOPLEA
Order Dorylaimida
Family Longidoridae
Longidorus spp. = “needle” nematodes, 130+ species
Paralongidorus spp.
Xiphinema spp. = “dagger nematodes”, 240+ species

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Agrios

Longidorus sp.
U. Zunke
Nemapix 1

Longidorus spp. = “needle” nematodes
Life cycle and biology
- Wide host range, mostly non-woody plants.
- Mint in Willamette Valley.
- Often occur deep in soil => 60-90 cm.
- Some species may live three years.

Longidorus spp. = “needle” nematodes
Symptoms
- Feeds at root tips and may produce galls.
- Roots are greatly stunted.
- Excessive branching may occur.
- Necrosis may occur.
- Top growth and yield are greatly reduced.
***Important virus vector.
Control
- Nematicides

Roots of table beets damaged by
needle nematode, Longidorus elongatus.
U. Zunke
Nemapix 2

Longidorus elongatus damage to peppermint

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS ENOPLEA
Order Dorylaimida
Family Longidoridae
Longidorus spp. = “needle” nematodes, 130+ species
Paralongidorus spp.
Xiphinema spp. = “dagger nematodes”, 240+ species

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Agrios

Xiphinema sp.

Xiphinema spp. = “dagger” nematode
Life cycle and biology
- Wide host range as a genus (primarily woody
species) but individual species may have a narrow
host range.
- Males are rare and probably not necessary for
reproduction.
- Reproduction in most species is parthenogenic.
- Life cycle may vary from 22-27 days to one+ years
- Can survive up to three years in soil without a
host plant.

Xiphinema spp. = “dagger” nematode
Life cycle and biology
- Can be particularly damaging on woody plants
=> tree nurseries, grapes, roses, figs etc.
- Some species favor sandy soils; others like clay soils.
****Important virus vectors.

Xiphinema spp. = “dagger” nematode
Symptoms
- Most species feed on cortex tissues at the root tip in
the zone of elongation.
- Root growth is severely disturbed and root tips
swell, gall and become brown.
- Epidermal and cortical cells collapse at the feeding
site, large multinucleate cells develop (with up to 9
nuclei/cell, dense cytoplasm, no vacuoles and
without thickened walls).

Dagger nematode and gall on fig root
U. Wyss
Nemapix 1

Xiphinema spp. = “dagger” nematode
Symptoms
-Nematodes may feed in one spot for a few minutes
or several days.
-Roots are stunted and if nematodes only feed on one
side the root may curve toward that side.
- Nutrient uptake may be inhibited, plants may
become chlorotic, lose leaves and appear unthrifty.

Dieback of maple sometimes associated with
dagger nematodes (Xiphinema sp.)
G. Thorne
Nemapix 1

Xiphinema spp. = “dagger” nematode
Control
- Fumigation
- Start with planting stock certified nematode-free
-Difficult to eliminate since it often exists on deep
roots - even if roots are detached from tops
=> escapes nematicides that cannot penetrate
that deep.
-Rotation works if crops are selected carefully,
weeds and volunteers are controlled and the
rotation is sustained for 4-5 years.

DISEASES OF ROOTS
MIGRATORY ECTOPARASITES
CLASS ENOPLEA
Order Triplonchida
Family Trichodoridae
“Stubby-root” nematodes
Trichodorus spp., 55+ species
Paratrichodorus spp., 44+ species

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Agrios

Paratrichodorus allius

Trichodorus/Paratrichodorus – “stubby-root”
Life cycle and biology
-P. christei first ectoparasite = economically important
1951.
- Wide host range
- Beets, celery, sweet corn.
- Locally Paratrichodorus allius is important on onions.
-Cosmopolitan but more important in tropics and
semitropics.
- Generally do best in sandy soils.

Trichodorus/Paratrichodorus – “stubby-root”
Life cycle and biology
- Can be found 40-100 cm deep.
- Good at migrating vertically.
- Males important in some species but not in others
-
- Life cycle of P. christei and P. minor is 3 weeks at 22 C,
2.5 weeks at 30 C up to 6 weeks at cooler temps.
- T. primitivus = 45 days at 15-20 C

Trichodorus/Paratrichodorus – “stubby-root”
Symptoms
- Root tips fed on cease to elongate, become stunted
- Lateral roots emerge from behind root tip, these are
also fed upon, become stunted and generate lateral
roots of their own => root proliferation.
- Root cap is destroyed, reduction in region of
maturation, some swelling possible.
=> results in system of short, thick segments or stubs.
-Tops develop poorly, wilt easily and produce low
or no yields.
****Important virus vector.

Trichodorus/Paratrichodorus – “stubby-root”
Control
- Fumigation and nonfumigant nematicides
- Occasionally reported to increase rapidly after
fumigation to higher numbers than before fumigation.

Disease cycle of stubby-root nematode
Agrios

Stubby-root Nematode
Damage to Corn Roots
K.R. Barker

Sugar beet damage (left, middle) caused by the
stubby-root nematode, Trichodorus similis.
U. Zunke
Nemapix 1
SON
Nemapix 1

Paratrichodorus allius damage to onion