Q How do I recognise virus infection?
A Initially the symptoms can be very subtle – a gradual decline in the crop, perhaps a little stunting, distortion or discolouration.
As the disease builds up, the symptoms become pronounced and crop production may suffer. The leaves become mottled, with yellow patches between the veins.
Caption: Virus stunts or distorts the plants and reduces the crop
Q This symptom sounds very similar to mineral deficiency. How can I tell them apart?
A Leaves suffering from iron or magnesium deficiency can look like those with a virus infection. It is more likely to be a deficiency if all the plants are affected, regardless of variety, or if the problem occurs within the first year or two of planting.
It is more likely to be a virus if the plants are also stunted or are distorted, and if the crop is very poor. Another factor that suggests a virus infection is when some varieties are affected more than others.
Q Tell me more about viruses
A All cane fruit can be affected, but raspberries are particularly susceptible. The most common problem is raspberry mosaic disease, caused by a combination of viruses spread by aphids. The plants may still crop reasonably at first. Leaf symptoms can be varied but typically consist of angular, yellow areas between the veins.
Raspberry yellow dwarf virus is caused by arabis mosaic virus, spread by eelworms in the soil. Plants are stunted with little fruit. The leaves have small yellow spots and yellow patches along the veins. Scottish leaf-curl disease is caused by raspberry ringspot virus. It causes yellowish rings on the leaves, which curl downwards and may be brittle or stunted.
Q How do I control them?
A There is no treatment for virus-infected plants. They should be dug out and burned.
Q What can I do to prevent viruses?
A If you are buying new plants, ask for certified stock; thus should be virus-free. When planting a new raspberry bed, site it away from soil where they have grown before; eelworms can survive for years and travel up to 15m to infect new plants. If this is impossible the only alternative is to replace the soil, taking out a trench 60cm wide and 45cm deep. The infected soil is safe for all other plants except strawberries.