Nematode Pests of Horticultural Crops and their Management (1+1)

Spices

SPICES
India is the major producer of number of spices like black pepper, cardamom, ginger, turmeric, cloves, cumin, cinnamon, nutmeg, coriander, fenugreek etc.
I. BLACK PEPPER
Black pepper has its origin in the hills of South-Western India. Though, about 40 nematodes species have been reported to be associated with pepper, only two, viz. Radopholus similis and Meloidogyne spp. are important as far as distribution and economic damage is concerned.

A. Radopholus similis:
C.O. ‘Yellows’ disease of pepper or ‘Pepper Yellow’ and the very similar 'Slow-wilt' disease of black pepper.
‘Pepper Yellow’ wiped out 22 million pepper vines from Bangka Island in Indonesia within 20 years. In India, pepper vines in Kerala and Karnataka suffer from frequent incidence of 'Slow-wilt' disease.
Hosts:

• Coconut and arecanut, on which black pepper vines generally trail, are good hosts of this nematode. Intercrops like banana, ginger and turmeric are also susceptible to R. similis.

Nature of Damage:

• It is a migratory endoparasite that penetrates roots within 24 hours of inoculation and remains within the cortex and does not enter the steler region.
• The cells around the site of penetration become brown.
  
• The xylem vessels are seen plugged with a "gum-like substance"

Symptoms:

• Initial appearance of a few pale, yellow, drooping leaves whose number gradually increases and within a year or two the entire foliage becomes chlorotic. Chlorosis is more pronounced under drought conditions.
• This is followed by shedding of leaves, cessation of growth and die-back symptoms.
• In large plantations, affected patches are conspicuous with many barren standards.
  
• Young as well as old plants are affected.
• In the very early stage, the symptoms may disappear with the onset of south-west monsoon.
• In bearing vines spike shedding takes place.
• Affected vines die within a span of three to five years.
• The tender, thin, white, feeder roots show typical orange to purple coloured lesions.
• The root system exhibits extensive rotting with the main roots devoid of feeder roots. Extensive necrosis of large roots develops subsequently.

Management:

• Chemical control of the nematode in black pepper is difficult due to perennial nature of the crop and in India, where other crops grown in mixed perennial multi-crop systems are all susceptible and repeated applications of the nematicides may not be economically feasible.
• Aldicarb sulfone at 8 kg a.i. per ha gave best control of R. similis followed by fensulfothion. Under Indian conditions, phorate@ 3 g per vine applied in May/June and again in September/October controlled the nematode over a period of three years.
• Mulching with dead leaves improves the symptoms of Slow-wilt/pepper yellows.
• For heavily infested areas, an integrated method of management is suggested.
• Planting nematode-free rooted cuttings
• Uprooting affected vines and replanting after 9-12 months
• Use of non-living standards and exclusion of R. similis susceptible trees as standards for trailing black pepper vines and avoiding susceptible intercrops such as banana, ginger, turmeric etc.

B. Meloidogyne spp.
In India, Butler (1906) was the first to report root-knot nematode from black pepper in Kerala.
Distribution:

• Meloidogyne javanica and M. incognita have been reported from almost all pepper growing nations of Asia including India. M. arenaria has been found on pepper in Sri Lanka.

Hosts:

• Most of the commercially used standards are highly susceptible to root-knot nematode. Large numbers of weeds found in pepper gardens are also highly susceptible to this nematode.

Nature of Damage:

• Sedentary endoparastic in their feeding behavior.
• J2s penetrate the meristmetic tissue, settle themselves in steler region and start feeding on pericycle cells. Feeding continues for weeks together with gradual swelling.

Symptoms:
Affected plants show prominently slow unthrifty growth and yellowing of leaves.
The interveinal areas of leaves turn dense yellow but the leaf veins remain distinct with deep green colour. The roots show prominent galls.
Management:

• Among various popular cultivars of pepper screened for resistance, only one cultivar CLT-P-812 has been found resistant to M. incognita.
• Paecilomyces lilacinus and Pochonia chlamydosporia when introduced to sterile soil before inoculation of nematodes to potted plants infected egg masses of M. incognita on black pepper seedlings.
• Under Indian conditions application of aldicarb@ 1 g a.i. per vine twice a year (May/June and October/November) integrated with fertilizers (N = 100g, P = 40g, K = 140g per vine) in two equal split doses, earthing up to 50 cm radius at the base of the vines and mulching the base of the vines reduces foliar yellowing by 83% and M. incognita larval population by 33-88%.

II. CARDAMOM
Cardamom has its origin in the evergreen rain forests of the Western hills of South India.
The most important nematode problem is the root-knot nematode, Meloidogyne spp.

Meloidogyne spp.

Distribution:
Meioidogyne incognita and M. javanica widely occurring in cardamom nurseries and plantations in Kerala, Karnataka and Tamil Nadu.

Host Range
Many annual weeds and common shade trees like Erythrina indica and E. lithosperma present in cardamom plantations are susceptible to root-knot nematodes.

Symptoms:

• In primary nurseries germination is reduced to less than 50%. Infected seedlings fail to establish in secondary nurseries.
• The roots show heavy galling.
• In secondary nurseries, infected plants exhibit stunting, yellowing, poor tillering and heavy galling of roots.
• Infested mature plants show stunting, yellowing, reduced tillering, delay in flowering, immature fruit-drop and reduction in yield.
• Interestingly, roots of matured plants do not show galling. Instead, they show excessive branching.

Management:

• The popular cardamom cultivars, Malabar, Mysore and Vazhuka are all susceptible to root-knot nematodes.
• Disinfesting nursery beds with methyl bromide @ 500 g per 10 m² is effective in controlling root-knot nematodes in cardamom nurseries. Seed beds can also be drenched with 2% formalin to a depth of 20-30 cms and covered with polythene sheets for three to seven days. Seeds can be sown two weeks after formalin application when the soil is free from formalin fumes.

• Application of aldicarb/carbofuran/phorate @ 5g and 10g a.i. per plant and neem cake @ 500g and l000 g per plant twice a year results in increase in growth and vigour of seedlings both in primary and secondary nurseries.

• Integration of the following practices can help in the successful nematode management.
• Changing nursery sites frequently
• Disinfesting nursery beds
• Introduction of biocontrol organisms at nursery level
• Control of susceptible weeds
• Exclusion of susceptible shade trees
• Destruction of infested crop residues
• Application of nematicide and neemoil cake
• Mulching with dead leaves

 

III GINGER
Though the country of origin of ginger is not known with certainty, it is presumed to be in the region of India or China. Nematodes that cause economic damage to ginger include Meloidogyne spp. and Radopholus similis. Pratylenchus zeae has been found to be a major nematode pest of ginger in Himachal Pradesh

A. Meloidogyne spp.
Nature of Damage:

• Second stage juveniles are infective. J2s penetrate fleshy and fibrous roots, form giant cells through which they suck the cell contents and develops to maturity within 24 days. But in rhizomes, it takes a longer period to mature.
• J2s attack the rhizome through axils of leaf sheaths in the shoot apex. Fleshy roots are invaded along the entire length, while in fibrous roots it is in the area of differentiation.
• Roots and underground rhizomes exhibit galling and rotting.
• Infested rhizomes help in long distance dissemination of nematodes.

Symptoms:

• Heavily infested plants show stunting and chlorosis, withering of aerial shoots and marginal necrosis of leaves.
• Infested rhizomes have brown, water-soaked areas in the outer tissues especially in angles between shoots.
• M. arenaria causes typical symptoms of drying and twisting of leaves

Fig. 16.1 Ginger rhizome infested with root-knot nematode

B. Radopholus similis

R. similis infestation in ginger was first reported in India, from Kerala. The perpetuation and dissemination of the nematode take place through infested rhizomes used for planting.
Nature of Damage:

• The nematode is a migratory endoparasite, penetrates through cell walls and is found coiled within a single cell.
• Due to infection, large channels or galleries are formed within the rhizomes.

Symptoms:

• Affected plants exhibit stunting, reduced vigour and tillering, and mature and dry out faster than healthy plants.
• The topmost leaves become chlorotic with scorched tips.
  
• The infected rhizomes exhibit small, shallow, sunken, water-soaked lesions.

Management:

• Application of well decomposed cattle manure or compost@ 25-30 tonnes per ha, neemcake @ two tonnes per ha, and mulching with green leaves @ 10-12 tonnes per ha at planting and mulching again during the growth period helps in reducing nematode population.
• Pre-plant hot water treatment of ginger rhizomes at 45^o C for one hour renders them nematode free.
• In Himachal Pradesh, application of phenamiphos @ 3 kg a.i. per ha resulted in 70-144% increase in yield of ginger in nematode infested fields.