Cereal Cyst Nematode of Wheat

Heterodera avenae

Family: Heteroderidae

Order: Tylenchida

Description:

Cereal Cyst Nematode (CCN) is a soil nematode causing yellowing or paling of young cereal crops and significant yield losses in some situations. On heavy fertile soils crops tend to lighter green in affected areas whereas on sandy soils the crops tend to be yellow. At early tillering affected plants are pale, slightly stunted with erect and duller leaves and reduced tillering. It often occurs in irregular shaped patches from 1 metre to 100 m in diameter. The roots tend to be tangled into a ball with the roots shortened and thickened and knotted with 1 to many, round, circular, tiny, initially white cysts at some of the knots. The cysts turn brown with age. Root symptoms tend to be seen on the seminal roots (arising from the seed) and sometimes later on the tiller or crown roots. Crops tend to apparently recover in spring when the more crown roots form. On Oat the typical "knots" may not form and the root system may be shallow with missing lateral roots and root hairs.
Each cyst contains hundreds of tiny, oblong, bullet like eggs and egg has a tiny juvenile nematode curled up inside which can only be seen under a microscope.
At 11-13 weeks after germination, female nematodes may be seen at the "knots" or thickened sections of the root.

Species Affected:

Spear, Halberd and Durum Wheat and Echidna Oats are significantly damaged by CCN.
Wild Oats are susceptible.
Barley, Cereal Rye and Triticale are tolerant and yield well despite being attacked.
Frame Wheat, Galleon and Sloop Barley, Wallaroo and Marloo Oats are resistant to CCN and stop it producing eggs.
Barley Grass, Brome Grass and Ryegrass are resistant and reduce soil populations of CCN.
Broad-leaved plants are tolerant.

Biology:

1 generation per year.

Life Cycle:

Eggs survive the summer in the soil in cysts. With the break of the season in autumn, and falling temperatures, around 85% of the eggs hatches over a period of 8-10 weeks to produce larva and the remaining eggs remain dormant. The larvae move in the soil water to penetrate the roots. This feeding causes the knotting symptoms on roots. The adults mate and in susceptible cereals the white females develop and swell with eggs laid inside their bodies producing the white cysts full of eggs that can be seen about 15 weeks after planting. The cysts turn brown and harden for the summer. This completes the cycle.

Origin and History:

Distribution:

NSW, SA, VIC, WA.

Significance:

The damage caused by CCN depends on the number of nematodes present in the soil, the tolerance of the crop, the soil fertility and the level of weeds.
Broadleaf plants reduce CCN populations.

Management and Control:

Do a PreDicta B soil test which is available from SARDI Root Disease Testing Service.
Plant tolerant Wheat varieties or CCN resistant Barley varieties that stop multiplication of CCN in the roots and thus reduce levels in the following season e.g. Sloop SA or Sloop Vic for malting and Galleon for feed.
See Disease Susceptibility of Wheat Varieties and HYPERLINK \l "_Disease_Susceptibility_of_Barley Va" Disease Susceptibility of Barley Varieties.
Control self-sown susceptible cereals and Wild Oats in break crops and pastures for at least 2 years.
Increase time between sowing susceptible cereals to at least 2 years.
Get a CCN Bioassay kit and take soil samples soon after harvest. This will give an estimate of likely damage to cereals in the following summer.
Fallows should commence in early August to prevent CCN reproduction.
Nematicides provide short-term protection and generally only protect the current crop without significantly reducing the population in the following year because late hatching nematodes will escape the nematicide treatment.
Maintain good soil fertility to reduce the impact of the nematodes.
Reduced tillage tends to decrease nematode problems.
Note the difference between resistant and tolerant varieties. Resistant varieties prevent the nematodes building up and affecting following crops and but they may be seriously affected by the nematodes in the current season. Tolerant varieties are not affected by the presence of the nematodes, that is, they tolerate it but may allow numbers to build up and affect subsequent crops.

Related and Similar Species:

Looks like nitrogen deficiency.

References:

1295

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.