Stem nematode

LEFT: Close-up of stem nematode affecting oat plant, showing stunting and multi-tillered effects with some death of leaves. RIGHT: Close-up of oat plant with abnormal bulb-like base of stem.

The value of pulses and oats as disease breaks to cereal cyst nematode and other major cereal root and leaf diseases is threatened by the spread of stem nematode in SA.

Stem nematode feeds on the emerging shoot, crown and above-ground parts of host plants, resulting in distorted and stunted growth. The population can build up rapidly as the nematode can reproduce four or five times in a season.

The nematode can survive and spread between districts in infected hay. It can also survive in the seed of some crops, especially faba beans. Localised spread is possible by soil contamination of stock and machinery and in surface water, wind-blown stubble or soil.

Stem nematode can survive in a dehydrated form in hay and seed for 10 years or more. Weeds can play a key role in the survival of stem nematode when there are no host crops. This explains why the nematode can recur after paddocks have not grown susceptible crops for a number of years.

The oat race of stem nematode has the widest host range including oats, peas, chickpeas and faba beans. High numbers can cause crop failure. Small numbers of the oat race can sometimes be found in Blanchefleur, Languedoc and Namoi vetch and lentils. Wheat, barley and triticale varieties are resistant.

Bettong and Echidna oats are both resistant and tolerant. All other oats are susceptible and intolerant.

Wild oats and cleavers are major weed hosts. Minor hosts include ryegrass, brome grass, soursobs, wild turnips and poppies.

The lucerne race (of stem nematode) attacks lucerne, onions and garlic.

What to look for

  • distorted and stunted plant growth — patches of 1-100 m in emerging crops
  • a plant or seed test is available through the Field Crops Pathology Unit, SARDI; contact Sharyn Taylor 08 8303 9381, or Chris Wilmshurst 08 8303 9384.

What to do

  • include resistant crops and varieties in planned rotations
  • control host weeds
  • observe farm hygiene
  • growers with a stem nematode problem should not grow oats in succession with faba beans or peas.

Stem nematode invades and sometimes damages resistant varieties like Echidna. Resistance starts to operate for to six weeks after emergence. The nematodes leave or die and the plants recover

However, if the plants are also invaded by CNN, Echidna will remain susceptible to stem nematode, resulting in crop failure. For further information contact Ms Sharyn Taylor, phone 08 8303 9381, fax 08 8303 9393.