Cucumber mosaic virus of lupins
Cucumber Mosaic Virus (CMV) is a very damaging viral disease of lupin crops. It can also infect a large range of non-cereal crops and pastures.
Recognising disease symptoms and taking appropriate control measures will reduce the risk of crop damage.
What to look for
The disease causes a stunting of any new growth produced after the plant is infected. If the virus is carried in the seed the entire plant will be stunted and may die before maturity.
A plant infected late in the season may have normal sized leaves at the bottom but those near the top, above the point of infection, will be less than half normal size.
The leaves on infected plants become bunched, curled down and chlorotic (pale in colour), particularly at the growing shoots.
Infected plants may occur randomly throughout the paddocks. Often they will be in small patches, 1–2 metres in diameter (Figure 1.)
Yield losses of almost 100 per cent can occur if most plants are infected at an early stage of growth.
The later the plants are infected the less effect the disease will have on yield. Yield reductions of 10 to 40 per cent are common in infected crops.
The disease is introduced to properties through infected seed.
Aphids then transmit the disease from infected plants to healthy plants in the crop. Aphids can transmit the disease up to 0.5km, although the usual distance for aphid transmission is far shorter.
Seed for sowing may have only a low percentage of infected seed (less than 1 per cent), but when aphids are present they can spread the disease from infected plants to other plants resulting in a rapid increase in the proportion of plants infected.
Approximately 10 per cent of seeds harvested from infected plants will carry the virus and, when sown, start the infection in the next crop. This may result in very large yield losses within 1 to 2 seasons unless control measures are taken.
The purchase and use of disease-free seed is the only practical option.
It is usually not economic to spray a crop for aphids to prevent CMV spread as the chemicals available have a short residual activity of 5 to 7 days. The repeated applications necessary to achieve the length of control required would be too expensive in most situations.
Any narrow leaf lupin crops that are harvested for seed should be examined for signs of CMV and classified into one of the following 3 categories.
- Signs of infection obvious – if CMV infection is obvious in a crop the harvested grain should not be used as seed. It may be sold through normal outlets for feed purposes. A new supply of clean seed should be purchased. The results of a CMV test on the seed should be requested from the seller.
- Possible low level of infection – grain needs to be tested to determine its suitability as seed. If no infection is found by the test then the grain may be used for seed purposes. If infection is detected then it is desirable that option 1 be adopted.
- No infection obvious
If there is any doubt then option 2 should be considered. Otherwise retain some of the harvested grain to sow your next crop and minimise chances of undetected infection spreading by using the following techniques:
- Grade out the small seeds before sowing as these are more likely to carry infection. The disease is not spread by grading or in grader dust.
- Use a high seeding rate (120kg/ha). A high plant density will help to crowd out the smaller plants which grow from infected seed and reduce the chance of aphids finding the infected plants and spreading the disease. Research indicates these seeding rates are an advantage with modern varieties regardless of disease.
- Ensure good broadleaf weed control as some of these weeds can harbour the disease and infect the crop.
- Grow a cereal barrier around the outside of a paddock which will reduce the chance of aphid transmitted infection from adjacent crops or pasture hosts.
Broadleaf (albus) lupin is not a source of seed-borne infection.
Practices now accepted as standard methods to minimise other diseases should also be used for CMV. These include:
- a 2-year break, or longer, before the same crop is sown in the paddock again
- barriers of distance between paddocks which prevent trash blowing or washing from this year's crop into the paddock which will be sown to the same crop next year
- controlling self-sown plants which can harbour the disease after harvest.
There are a number of varieties that are moderately resistant to CMV seed infection. However, they are still susceptible to CMV by aphid transmission, but have a reduced risk of transmitting CMV through infected seed.
See the Pulse disease guide for information on resistance.
A sample of grain can be submitted for a test that will show the percentage of seeds that carries the CMV disease. It is vital that seed purchased does not introduce CMV to the property.
Seed tests can be obtained by sending a representative sample of seed for CMV seed testing.
Seed testing laboratories
- Crop Health Services, Agriculture Victoria, (03) 9032 7515
- DDLS Specimen Reception, DPIRD, (08) 9638 3351, DDLS@dpird.wa.gov.au
The CMV can be combined with other tests such as germination, seed weight and other seed borne diseases. Seed test results will be available within 2 to 3 weeks.
It is sensible to only sow seed with no detectable level of CMV. Even infection levels of less than 0.5 per cent have resulted in substantial yield reductions in the subsequent crop. Assistance in interpreting the results of tests can be obtained from the department.
- Pulse disease guide
- Victorian crop sowing guide
- Seed health testing in pulse crops
- Winter Pulse Disorders: The Ute Guide
- Lupin Southern Region – GrowNotes
- DAFWA Cucumber mosaic virus in narrow-leafed lupins
Dr Piotr Trebicki
Virologist – Horsham
03 5450 8301
Field Crops Pathology
Grains Innovation Park
110 Natimuk Rd
03 5450 8301
Or call the Customer Service Centre, 136 186
Ivan Mock (Future Farming Systems Research), Frank Henry (Farm Services Victoria). Support by the Grains Research and Development Corporation is gratefully acknowledged.