Root lesion nematode
Grant Hollaway (Victorian Institute for Dryland Agriculture)
Root lesion nematode (RLN) can cause large grain yield losses, particularly in wheat and chickpea crops. At least 20% of cropping paddocks in south eastern Australia have populations of RLN high enough to reduce yield. RLN can be effectively managed with rotations.
Root lesion nematodes (Pratylenchus species) are worm-like organisms less than 1 mm in length which feed on root tissues. Unlike cereal cyst nematode (CCN), RLN has more than one generation per season and is able to migrate between and within the roots and soil. These nematodes survive over summer in a dehydrated state, becoming active again once moisture is available.
There are two species of Pratylenchus that are important - Pratylenchus thornei and P. neglectus. The two species of nematode often occur together. Both species are common in the Wimmera, while in the Mallee, even though P. neglectus is more common, P. thornei does occur.
RLN is not a new problem. They have been present in the soil for many years, but have not been recognised as a serious problem because their effects are difficult to measure. Also changes in crop rotations have favoured increases in RLN populations.
In the field, symptoms include stunted growth, uneven patches or waviness across the paddock.
The two main root symptoms include lesions or discolouration of the roots and lack of branching along the main roots. Unlike CCN, root lesion nemtodes do NOT cause the roots to swell or knot and no cysts are produced.
Yield losses are related to the initial populations of RLN in the soil at sowing and the tolerance of the crop to RLN (Table 1). In Wimmera grey soils infested with P. thornei, grain yield losses in wheat of 20% were measured in 1999. P. neglectus can cause yield losses greater than 20% in intolerant crops.
Surveys in the Victorian Wimmera showed high populations were present in some soils associated with a broad range of cropping programs. However wheat and chickpeas were implicated as the most significant contributors to population increases.
Surveys of cereal crops in south-west Victoria have found that RLN is of less importance than in other cropping regions.
Control of RLN is based on crop rotation. Rotations including resistant crops reduce the nematode population.
Susceptible crops are good hosts of RLN. When grown consecutively susceptible crops can lead to high nematode populations. However, there are variations in the hosting ability between different crops (Table 1).
- Rotations are the only practical way of managing RLN.
- Growing resistant crops can reduce nematode populations by up to 50% per year. Where levels are high, two or more years break may be necessary to minimise yield penalties.
- Tolerant crops suffer less yield loss than susceptible crops.
- Early sowing minimises yield losses.
- Fertile soils will increase the ability of crops to tolerate damage.
A soil test is essential to identify paddocks with high populations. Contact your local agronomist or Bayer Crop Science representative (03-54416932) for a Predicta B root disease soil test.
- Information notes series: Crops and Pastures, Cereals
- Hollaway G (2005) Agriculture note AG1160: Cereal Disease Guide
- Wallwork H (2000) Cereal Root and Crown Diseases.
- Wallwork H (1999) Cereal Disease: The Ute Guide.
|P. thornei||P. neglectus|
A - Resistant lines minimise nematode multiplication (R- Resistant, MR - Moderately Resistant, MS - Moderately Susceptible, S - Susceptible)
B - Tolerant lines suffer minimal yield loss in the presence of the nematodes (I - Intolerant, MI - Moderately Intolerant, MT - Moderately Tolerant, T - Tolerant). Many crops vary in their resistance/tolerance (eg wheat S-MR) depending on the variety.
C - Ratings for more wheat and barley varieties are available in a current “Cereal Disease Guide”
* Based on limited data. Table compiled using information of G. Hollaway, S. Taylor (SARDI) and V. Vanstone (University of Adelaide).