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Common name
Root knot nematode or eelworm.
Scientific name
Meloidogyne species, including M. arenaria, M. hapla, M. incognita, M. javanica.
Introduction
Potatoes are very susceptible to root knot nematodes which have a broad host range and are the most economically damaging of all the nematode species to agricultural crops world wide. Root knot nematodes prefer warm temperatures and are likely to become established in potato crops grown in relatively warm areas in the north and north west of Victoria. Generally, they are not a major problem in traditional cool climate potato production districts but have become established in some localised areas. The greatest losses occur where potatoes are grown intensively or rotated with other susceptible crops.
Figure 1. Root knot nematode on potato tubers. Symptoms include blisters or swellings giving the tubers a warty appearance.
Symptoms
Infested potato plants may show varying degrees of stunting, yellowing of leaves and a tendency to wilt under moisture stress. Roots have swellings or galls, and beads or knots (hence the common name). Affected tubers have blisters or swellings. Symptoms are most severe when crops are grown on sandy soils and warm climates above 25C.
Root knot nematode reduces the quality, size and number of tubers. Infested potatoes can become more susceptible to bacterial wilt, Pseudomonas solanacearum, and symptoms are more severe when plants are also infected with fungal pathogens such as Verticillium and Rhizoctonia.
Description
Nematodes or eelworms are small (less than 1 mm in length) soil-borne pests which attack plant roots. They are the most common multicellular organisms in soil.
Biology
Juvenile nematodes hatch from egg masses (eggs surrounded by a gelatinous layer) deposited by females. Juveniles move through the soil to the plant roots where they use a needle-like stylet to puncture roots (just behind the root tip) and suck out the cell contents. After entering the plant, the juvenile nematodes undergo a series of moults. On becoming adults, the males leave the roots while the females stay in the roots and continue to feed.
Invasion and feeding by the female nematode stimulates the host cells to enlarge and multiply into giant cells, causing the galls on the roots. Once a female nematode establishes a feeding site, her body enlarges and protrudes through the root. After mating with a male she lays eggs in a sticky substance on the outside of her body. Some species of root knot nematode can produce eggs without males. In temperate climates, generation time is four to six weeks and there are usually three or four generations per year.
Survival
Nematodes survive in the soil as egg masses. The gelatinous layer around the egg masses provides protection against desiccation and chemicals. Each female produces 500 -1000 eggs. Eggs hatch under favourable conditions and juvenile nematodes infest roots of potatoes and other host plants. Root knot nematodes also survive in the absence of potatoes by infesting alternative hosts, including many weed species. Few species, except M. hapla, can survive extreme cold.
Dispersal
Root knot nematode may be spread by planting infested tubers. Potato tubers may be infested but not show symptoms. Symptoms may develop when tubers are stored, particularly when exported to warmer climates where nematode numbers can rapidly increase. Egg masses may be transported into clean paddocks via soil adhering to farm machinery.
Host range
Potato (Solanum species) and over 2000 other plant species, including many species of vegetables and weeds.
Control
There are no potato cultivars that are resistant to root knot nematode. Chemical control is difficult and may not be economical for most Victorian potato growers.
Use the following methods to control root knot nematode:
- Monitor crops for symptoms of root knot nematode infestations.
- Practise good farm hygiene.
- Avoid planting susceptible crops in paddocks contaminated with root knot nematodes.
- Rotate crops with resistant, immune or non-host crops such as grasses (sudan grass) or cereals (barley, rye, wheat) in combination with a weed-free fallow to reduce nematode numbers. Many pasture legumes, such as white clover, and the common weed fat hen or Chenopodium sp, are very susceptible to root knot nematode.
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Correct diagnosis is essential for effective pest and disease control.
For further information, phone Crop Health Services on (03) 9210-9356 or fax (03) 9800 3521.
For further information on registered chemicals, phone DPI Chemical Information Service.
Acknowledgment
Original author: Jillian Hinch, La Trobe University, Bundoora, previously edited by Kathy Pullman.
The previous version of this note was published in April 1999.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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