Nematode problem and its mangement

Y. S. Chandel

Department of Entomology CSKHPKV, Palampur-176062

What are nematodes?• The word nematode is derived from Greek words- Nema

meaning thread and oides means resembling or forms.

• Nematodes are also known by different names such as threadworms, roundworms, eelworms and nema.

• Nematodes constitute the largest group of animal kingdom comprising 80-90% of all multicellular animals

• These organisms are basically aquatic but have adapted terrestrial habits.

Where nematodes are found ?

Nematodes as a whole live under a variety of conditions and are known to occur everywhere where life can exist, from arctics to tropics, from heights of mountains to depths of oceans, they may be free-living in soil or in water (fresh, marine and brackish) or may live as parasites on animals including man or on plants.

Parasites of man/animals

• Ascaris• Hookworm• Guinea worm• Liverfluke etc.

Ascaris lumbricoidesAscaris lumbricoidesAscaris lumbricoides

Dracunculus medinensis

Plant parasitic nematodes

• The plant nematodes or phytonematodes are those seen associated with plants and constitute one of the most important groups of organisms which live in soil around the roots of plants.

• Compared to human or animal parasitic nematodes like filarial worm or ascaris, they are very small, about 0.01 to 1.00 mm in length. They are usually long and slender excepting in the case of females of some sedentary parasitic where they are enlarged and swollen and may be spherical, oval, lemon-shaped or kidney-shaped.

Where nematodes are confined in agricultural soils ?

• In agricultural lands, plant nematodes are usually confined to the top 20 to 25 cm of soil though this is variable according to the type of soil, moisture content , host plants and climatic conditions

• The citrus nematode, for instance, can occur at the depths of 2 to 2.5 m and the burrowing nematode at 3 to 4m.

• The surface soil does not harbour any nematode, since moisture and temperature fluctuate very widely in this layer. In all cases the nematode distribution in soil is governed by that of the host roots.

Mechanism of damage

• All plant parasitic nematodes possess a buccal stylet or spear. It is a sharp pointed protrusible organ which can be moved forth and back by means of muscles attached to its base. It is used to puncture the plant cells.

• Before sucking the sap the nematodes injects some quantity of its saliva into the cell. The enzymes contained in it predigest the cell contents. It is phytotoxic in varying degrees in different nematodes and is responsible for many of the visible symptoms in the infected plants.

Ways of damage by nematodes in plants

As primary pathogens: In most cases plant nematodes are themselves primary pathogens through draining of cell sap, dissolution and destruction of cells and disorganization of conducting vessels of pants which are consequently devitalized and show retardation of growth.

Association with other pathogens: Often nematodes are associated with other pathogens like fungi, bacteria and viruses in causing diseases. It is well established the role of nematodes in disease-complexes is more. The punctures made by the nematodes are used by the microorganisms for entering in the plant system.

Altering the host physiology: Nematodes can alter the physiology of the host in such a manner that, when both nematode and fungus are present, the damage caused by them is much more than that could be caused by the nematode or the fungus when it occurs alone.

As vectors of virus diseases: Some species of nematodes are known to transmit soil-borne viruses.

Life cycleThe plant nematodes have six stages, an egg,

four larval and an adult stage. The larva undergoes first moulting inside the

egg itself and the second stage larva come out to undergo three more moults before becoming the adult.

The average number of eggs laid by a nematode is about 200 to 500.

The life cycle is completed in 20 to 40 days in many cases.

Why the nematode problem is severe in polyhouses ?

• Congenial temperature(25-350C)• Availability of good moisture conditions in the

soil.• Light soils

Some observation by the university scientists

Total polyhouses analysed to know the gravity of nematode problems = >450

Presence of mainly root knot nematode. Less infestation in the newly started polyhouses.

High incidence of the nematodes is associated either with crop failure or poor crop stand in many cases.

Lack of proper knowledge to the farmers about nematodes.

Sources of inoculums

• Through infested implements.• Irrigation water• Through insects

Above-ground Symptoms of nematode damage1. Stunting: Stunting of plants is usually seen in patches.

2. Yellowing: Damage to the root system due to nematode feeding adversely affects the uptake and translocation of nutrients upwards.

3. Wilting: Nematode damage to the vascular tissues disrupts the flow of water to the foliage. This is most commonly noticeable in broad-leaved plants. When leaves wilt during hot weather despite the presence of enough moisture in the soil.

4. Dieback: In perennial crops like most fruit trees, general symptoms of dieback, i.e. gradual shedding of foliage from tip downwards, premature shedding of fruits, undersized fruits, weak seasonal flushes.

5. Dead or devitalized buds: Feeding on the terminal bud or the growing point may result in a ‘blind’ plant, if it is totally destroyed e.g. Aphelenchoides fragariae on strawberry.

6. Crinkling and curling of leaves: Constant irritation and ectoparasitic feeding by the nematode on the newly emerging leaves.

7. Leaf spots, lesions: Foliar nematodes like Aphelenchoides ritzemabosi enter through stomatal openings and feed on the mesophyll tissues of leaves.

3

Patchy growth due to Root Knot Nematodes

Okra

Below-ground symptoms1. Root galls: The root-knot nematode, Meloidogyne species produce galls or

knots on the roots, which is very characteristic and diagnostic of this nematode.

2. Reduced root system: Nematode feeding on the root tips may kill the growing point and stop the further elongation of root.

3. Root lesions: Elliptical necrotic lesions are chiefly produced by lesion nematodes, Pratylenchus spp. As the infection spreads, adjacent lesions may coalesce and ultimately girdle the root making the terminal portion of the root defunct.

4. Root rot : This is generally the result of secondary organisms which cause decay of the fleshy underground tissues damaged by nematodes initially.

5. Excessive root branching: Nematode infection may sometimes stimulate the plant to produce branch rootlets near the sites of penetration, resulting in excessive root branching.

6. Swellings: Besides branching, the roots also show slight swellings at the sites of nematode infection. Such roots appear bushy.

Roots infested with Root Knot Nematode (Meloidogyne incognita)

Brinjal Tomato

Management of nematodes in polyhouses

• Phytosanitary measures• Soil testing for the nematodes at least twice in a year.• Sampling methodology• Raising of the healthy nursery • Post harvest ploughing and maintenance of dry soil

conditions• Do not keep the polyhouse open.• Sterilization of implements used in other infested

polyhouse/fields before their use.• Use of sufficient quantity of organic matter.• Use of crop rotation, if possible.

Chemical Management

• Use of the nematicides- Carbofuran(Furadan 3 G) OR Ethoprophos (Mocap) OR Prorate (Thimet 10G) at the time of transplantation of crops in vegetable crops in the soil having having nematode history.

• In carnation and other floricultural crops, the above nematicides can be repeated at the interval of 1-2 months depending upon the nematode infestation.

• Treatment of the soil after the harvest of the crop with Formalin.

Dazomet treated Metham sodium treated

Untreated