DISEASE

NAME
Root Knot & Other Nematodes
Meloidogyne & other species


Description
Root Knot Nematode or eelworms are transparent thin nematodes that are an organism up to 0.5mm long and attacks the roots by injecting saliva that stimulates the surrounding cells to form galls. The adult male lives in the soil and the female are found in the roots, laying up to 2,000 eggs in a mass in the soil adjoining the roots.

     

Symptoms
Above ground the plant infected by Root Knot Nematodedevelops slowly and is stunted and the foliage loses its lustre and may turn yellow. The new growth is started and weak with fewer leaves. During hot weather the plant wilts easily as it is unable to keep up with the transpiration rate and under extreme conditions the plant dies. The young nematodes attack the roots forcing there way up the root tips forming galls. On inspection the galls are found centrally located along the roots and are up to 20mm across. The galls slow the rate of nutrients and water passing through the plant and as the galls break down they allow opportunity for other diseases to enter the plant.
The roots are severely damaged if the galls are physically removed.
Leaf feeding nematodesproduce angled lesions on broad leaf plants and narrow leaves tend to turn brown and die.

Other species of nematode include the Stunt nematode (Tylenchorhynchussp.), Lance nematode ( Hoplolaimussp.), Spiral nematode (Helicotylenchussp.), Lesion nematode (Pratylenchussp.), Cyst nematode (Heteroderasp.) and the Ring nematode (Criconemasp.) All of these nematodes have simular symptoms and are individually discussed below.
Note: root rot fungi or bacteria and other plant diseases, commonly infected roots that have been damaged by nematodes and certain viruses can also be transmitted by nematodes.

Source and Dispersal
The nematodes are found in soil or in infested plants and are dispersed by water, soil movement and attached to tools or shoes. The only way to determine the type of nematode in the soil is with laboratory tests.

Nema Head

Favoured Conditions
It prefers sandy soil types and a warm moist weather conditions.

Life Cycle
The microscopic nematodes have a life cycle that includes one egg stage, for juvenile stages and one adult stage and overwinter in the egg phase inside the dead female body or in plant material. Root rot nematodes produced on deposit eggs outside their bodies, while other species retain the eggs within their bodies such as Cyst nematode (Heteroderasp.).


     
Affected Plants
A wide range of plants are attacked by the Root Knot Nematode including tomatoes, potatoes, carrots, tobacco, hibiscus, gardenia and roses. Some species of nematodes are plant specific such as (Meliodogyne incognita) which attacks Hemerocallis, Celosiaand Violaspecies, forming small wart-like swelling on the roots.

Alternanthera, Begonia, Dianthus, Psidium, Thunbergia andWeigelaspecies are attacked by the Root Nematode(Meloidogyne incognita). This forms small swellings on the roots causing the top growth to be stunted and not responding to improved culture. In cool climates it is found on plants in glasshouses.

Buxusspecies are attacked by the Meadow Nematode(Pratylenchusspecies) that turn the leaves a bronze colour and cause stunting of the plant. These microscopic nematodes enters through the roots and eventually result in the death of the plant.

Lagunaria patersoniiis attacked by a simular nematode, the Root Burrowing Nematode(Radopholus similis) that feeds by burrowing in the outer root tissue.

Lavandulaspecies that are grown in the northern United States are susceptible to the Peanut Root Knot Nematode(Melioidogyne hapla). Berberisspecies are also susceptible.

Nothofagus obliquaand Nothofagus procera are attacked by the nematode (Subanguina chilensis) which attacks the roots and causes premature defoliation of the tree and making it susceptible to secondary pests and diseases and reducing its overall vigour. There are no control methods in a forest situation.

Tulipa species are attacked by Bulb and Stem Nematode(Ditylenchus dipsaci) which forms brownish streaks along the stem that may blister and may cause wilting. The flowers petals become distorted and the general vigour of the plant poor.


      Nematodes damage

Turf Grassare susceptible to several Parasitic Nematodesincluding (Helicotylenchusspecies), (XiphenemaSpecies), (Hemicycliophoraspecies) and (Ibiporalolii). All turf grasses are susceptible and the nematodes are active from spring to autumn requiring a soil temperature 15 şc. The leaves become chlorotic and have a weak appearance as a result of the damaged roots. Generally it is only a major problem when the nematode numbers are very high, otherwise control is not warranted.

Cultural Control
Crop rotation in infected soils, avoid using plants from the Brassicaceae family for up to four years and plant species that are tolerant of nematodes, this will reduce numbers. Beds may be laid fallow for several seasons to deter nematodes, but numbers build up quickly once susceptible plants return.
Affected plants such as roses may have the bare roots dipped in hot water 45şC for 15 minutes during the dormant period and contaminated growing media can be heat treated at 60şC for 30 minutes before being used.
Any infested plants should be removed and destroyed or deposed off site.

Improve the soil structure by mulching and avoid acidity by the addition of lime or dolomite. Garden beds may also be pre planted with marigolds or mustard to deter nematodes, but should be removed prior to planting as they can push nematodes towards the crop. Green manure crops may be grown prior to planting and infested soil may require up to three seasons of manure crops to bring nematodes under control.

BiologicalControl
The encouragement of earthworms reduces nematode numbers as they accidentally eat them in there normal course of growth and the addition of organic material in the soil encourage the natural enemies of nematodes such as fungi and predator nematodes.

Chemical Control
The soil can be treated with a nematicide such as fenamiphos in a domestic situation. Commercial growers may fumigate the soil prior to planting with the appropriate chemicals sterilising the soil. All the chemicals used are toxic and harmful to beneficial soil organisms.
Note
Always read the label for registration details and direction of use prior to application of any chemicals.