Stem Nematode
Ditylenchus dipsaci

Names:

Bulb nematode.

Onion Bloat.

Tulip root.

Description:

A nematode that attacks a wide range of species. The nematode is a tiny, long, thin worm like organism that can only be seen with a lens or microscope. It attacks the above ground portions of the plant including the crown and base of the stem. Stunted plants and poor emergence of crops is often seen.

Grasses

On grasses there is brown streaking on some leaves. Death of older leaves and increased tillering of giving the appearance of a swollen crown. There may be bulb like growths at the base of the plant and deformed shoots arising from ruptured coleoptiles occasionally. Coleoptiles may lie flat on the ground after emergence. Tillers are stunted, distorted and often more numerous. With very high nematode numbers there may be poor emergence and poor survival of seedlings. A brown rotting at the base of the plant appears as the season progresses and by the end of the season crops may lodge.

Bulbs

Brown rotted rings or stripes can be seen in infected bulbs when they are cut in half. New leaves are twisted and distorted and have raised ridges that may be yellow and are called spikkels and are full of nematodes.

On Tulips symptoms are more difficult to see and may show as grey to brown spongy areas on the outside of the bulb. Pale streaks and distortion may appear on the flower stem and flowers. Blisters and splits may also appear.

In Chives, Garlic, Leeks, Onions and Shallots seedlings may fail to emerge or have thick, distorted leaves or the plants may be stunted and wilted with later infections.

Canola

Leaves of young plants are distorted and compacted giving the crown a swollen appearance. It usually occurs in patches and in severe cases emergence may be reduced. Older plants are relatively tolerant. It looks like hormone herbicide injury especially when it affects large areas.

Species Affected:

Bedstraw, Beetroot, Cleavers, Canola, Common Chickweed, Daffodils, Faba Beans, Field Pea, Hyacinths, Jonquils, Lentils, Lucerne, Mouse-eared Chickweed, Oats, Onions, Parsnips, Peas, Potatoes, Strawberries, Teasel, Thyme-leaved Sandwort, Tulips, Vetches, Wild Oats and probably other plants as well.

The Oat race has been found on Oats, Bedstraw, Beetroot, Cleavers, Common Chickweed, Faba Beans, Hyacinths, Mouse-eared Chickweed, Onions, Parsnips, Peas, Potatoes, Teasel, Thyme-leaved Sandwort, Vetches and Wild Oats.

Avon, Irwin, Swan and West Oats are susceptible and intolerant.

Dolphin and Echidna Oats are intolerant.

Cassia, Marloo, Moore, N.Z. Cape, Saia, Sual, and Wallaroo Oats are tolerant to medium populations of the nematode.

No Oat cultivars exhibit high levels of tolerance and resistance. Tolerant varieties are used in the UK.

Field Peas and Faba Beans have no known resistant varieties.

It does not reproduce on Wheat or Barley and reproduces at low levels on Cereal Rye.

Beetroot, Cabbage, Cauliflower, Lettuce, Spinach and Triticale is also tolerant.

Daffodils are relatively tolerant to the Onion race of the nematode.

Biology:

4-5 generations per year.

Lives in the soil.

Attacks the above ground parts of the plant and doesn't attack roots but will attack bulbs.

It requires moisture to move in the soil.

The main method of spread between districts is probably in oaten hay. Local spread may be due to soil movement on stock or machinery or in water flows.

Wild Oat populations that have been exposed to the nematode develop a high level of tolerance within 10 years.

May be introduced by planting infected bulbs in gardens.

Resting nematodes are tolerant to frost, desiccation and high temperatures.

There are number of different forms.

Survives in stubble, plant tissue and the seed of Beans.

Life Cycle:

The young nematodes emerge from infected stems in autumn after the rains and swim in the soil moisture to infect the coleoptile of germinating seedlings. This may cause the coleoptile to lie flat on the ground. Once inside the plant it mates and reproduces, completing a life cycle in around 20 days. It survives over summer in a resting state in straw, seed or plant tissue and many can aggregate to form "eelworm wool". In this state it can withstand, drying and high temperatures for many years.

Origin and History:

Distribution:

Usually a patchy distribution within the crop but occasionally rather uniform over the whole paddock.

The Oat race of the nematode occurs in SA. An unknown race occurs in Victoria. Stem Nematode has not been seen in NSW or WA.

Significance:

May cause total crop failure in Oats and Peas.

Management and Control:

Cereals

Sow resistant Oat varieties.

Rotate to resistant crops to reduce nematode numbers.

Don't move infested plant material to clean areas. For example don't feed infected Oaten hay in clean paddocks.

Test Faba Bean seed for nematodes before planting.

Control Wild Oats and Bedstraw.

In infested paddocks don't plant Oats, Peas or Faba Beans for several years.

Systemic nematicides are effective but rarely economic.

Bulbs

Destroy badly damaged bulbs.

Treat with hot water.

Use a nematicide on infected soil.

Rotate to tolerant plants.

Related and Similar Species:

It looks similar to hormone herbicide injury and some viral infections. (Viral infections often cause pod distortions which helps distinguish them.)

References:

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Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 for more information.