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


LIFE CYCLE



CLASS CHROMADOREA 

Order Rhabditida 

Suborder Tylenchina 

Infraorder Tylenchomorpha 

Family Dolichodoridae 

Dolichodorus = “awl” nematodes, 16 species 

Based on shape of stylet








Belonolaimus = 10 species 

Belonolaimus longicaudatus = “sting” nematode

* 

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.


Stylet thrusts deep 

into roots 

= local lesions 

Soybean 

Stubby or coarse roots 

may be present 

L.I. Miller 

Nemapix 1


-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


Plants wilt, appear chlorotic and are reduced in size. 

In severe infestations the entire crop may die. 

L.I. Miller 

Nemapix 1


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.


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








Tylenchorhynchus = “stunt” nematodes, 130+ species 

Several morphologically similar genera, 250+ species

* 

Agrios

Tylenchorhynchus sp. 

U. Zunke 

Nemapix 2

Tylenchorhynchus = stunt nematode 


-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







Family Hoplolaimidae 

Hoplolaimus = “lance” nematodes, 30+ species

* 

Agrios

Hoplolaimus 

1-2 mm in length

Hoplolaimus = “lance” nematodes 


-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.



- 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.


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


Control 

- Soil fumigation 

- Nematicides 

- Dips for sprigs of Bermuda grass. 

- Fallowing may help but H. columbus survived storage 

in dry soil for 5 years.







Family Hoplolaimidae 

“Spiral Nematodes” 

Scutellonema spp. 

Rotylenchus spp. – 80+ species 

Helicotylenchus spp. – 160+ species

* 

Agrios

Scutellonema 


- 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 


- 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 


- 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.


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.


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.







Family Tylenchulidae 

Paratylenchus spp. = “pin” nematodes

Paratylenchus sp.

Paratylenchus sp.

* 

Agrios

Paratylenchus spp. = “pin” nematodes 


- 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.



- 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.


Control 

- Control seldom warranted unless in very high 

densities. 

- Nematicides only known control. 

- Appear to be more resistant to nematicides than most 

nematodes.







Family Criconematidae 

Criconemoides spp. = “ring” nematodes 

Also been known as: 

Criconemella 

Mesocriconema 

Macroposthonia

* 

Agrios

Criconemoides = “ring” nematodes 


- High populations damage roots of grape, pine, elm, 

maple, peach. 

- Also attacks many other crops but is less serious.


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.


Control 

Nematicides







Family Hemicycliophoridae 

Hemicycliophora spp. = “sheath” nematodes

* 

Agrios

Hemicycliophora sp.

Hemicycliophora = “sheath” nematodes 


-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.



CLASS ENOPLEA 

Order Dorylaimida 

Family Longidoridae 

Longidorus spp. = “needle” nematodes, 130+ species 

Paralongidorus spp. 

Xiphinema spp. = “dagger nematodes”, 240+ species

* 

Agrios

Longidorus sp. 

U. Zunke 

Nemapix 1

Longidorus spp. = “needle” nematodes 


- 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



CLASS ENOPLEA 

Order Dorylaimida 

Family Longidoridae 

Longidorus spp. = “needle” nematodes, 130+ species 

Paralongidorus spp. 

Xiphinema spp. = “dagger nematodes”, 240+ species

* 

Agrios

Xiphinema sp.

Xiphinema spp. = “dagger” nematode 


- 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.



- 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.


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


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


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.



CLASS ENOPLEA 

Order Triplonchida 

Family Trichodoridae 

“Stubby-root” nematodes 

Trichodorus spp., 55+ species 

Paratrichodorus spp., 44+ species

* 

Agrios

Paratrichodorus allius

Trichodorus/Paratrichodorus – “stubby-root” 


-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.



- 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


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.


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

DISEASES OF ROOTS MIGRATORY ECTOPARASITES

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