Capsicum diseases

Spotted wilt, which was covered in a previous article, is but one of 17 viruses found in peppers worldwide.

Capsicum diseases
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Five, including spotted wilt, occur in South Africa and each can wipe out a capsicum crop. We’ll look at two of these viruses in this article.

Pepper mild mottle Virus

The main way in which pepper mild mottle virus (PMMoV) is spread is via seed collected from the previous crop. The severity of symptoms varies from one cultivar to another, with some showing only a slight susceptibility. The infected plant is slightly stunted and noticeably lighter in colour, especially on the leaves between the veins. The fruit is also deformed.

The virus is carried on the seed coat and one infected seed can spread the virus to other seeds in the container. However, PMMoV is unlikely to come in with hybrid seed from reputable seed companies. The virus is easily spread from plant to plant by farm workers through their hands and clothing. Samples of other varieties from across our borders can also carry the disease. The virus can even be spread by sauces containing chilli or paprika, such as Tabasco. Farm workers using
chilli products on their food at lunch break can be a source of infection. It can even remain viable after passing through the human intestine.

If you collect your own seed and find symptoms in the land, you can easily get rid of the virus through seed treatment. In fact, if there’s any risk at all of PMMoV being present, treat the seed anyway. Make up a 10% solution of trisodium phosphate (TSP) with water and soak the seed for two hours, stirring occasionally. Then rinse it in running water – using a hosepipe and a bucket – for 45 minutes, and dry or plant immediately to ensure quick germination.

Tobacco mosaic virus

Unlike PMMoV, tobacco mosaic virus (TMV) is not confined to capsicums, but is also a major disease of tomatoes, tobacco and several weeds. However, with modern seed production methods it’s highly unlikely to come from seed, even though it is also seed-transmitted. TMV is more likely to be introduced by workers using snuff, or through physical contact with plants such as tobacco, tomatoes or (rarely) weeds.

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The latter could have acquired the disease from the previous generation. As its name suggests, TMV is usually more of a problem in areas where tobacco is grown. As with PMMoV, certain capsicum varieties are more susceptible than others to TMV. Given a susceptible cultivar and the odd infected plant, TMV can spread rapidly, especially with frequent handling.
Affected plants are stunted, paler and have distorted leaves.

Prevention and treatment
As with PMMoV, this virus can be spread via seed collected from the previous crop. It can also be treated in the same way, with equally satisfactory results. If you have an outbreak of TMV, rinse the equipment and staking poles in a solution of household bleach. If there is a risk of this virus on your land, choose a TMV-resistant variety if possible.

General guidelines to prevent the spread of viruses
It’s good practice to remove plants displaying symptoms of any virus. While doing this, avoid all physical contact with healthy plants. Place the infected plants in a heap and burn them – even dead, dry plants can infect healthy ones. If you have been in contact with the virus, wash your hands in milk or a solution of household bleach, and remember to wash your clothes too.