Shrivelled Tomatoes

‘Dear Dr Kris,
I have been trying to grow tomatoes many times here in Bali with very little success. Using seed I bought, or using seed from a fresh tomato washed and dried. Usually the plants start well, then when it’s almost ready to bloom, some leaves show tracks like a tiny insect is burying tuners inside it. This goes on until the plant shrivels and dies. I have tried many things, like always using a new pot, new soil, and new location, the end result is always the same. Can you explain what is happening.
Thank you, Jules.’

Growing tomatoes in a tropical climate can have its difficulties. The tomato, originally from South America, can grow year round in warm climates though dry season crops are definitely much easier to deal with compared to growing them in the wet season. The humidity of the wet season can cause so many problems, so if you’re not experienced it is much better to try and grow them in the dry season.

It sounds like your plant either has fusarium or verticillium wilt, which display similar symptoms and are both caused by different types of fungus that live in the soil. The fungus starts by attacking the plants at the roots and then gradually works its way up to the top of the plant. The first visible signs of infection are just as you describe, you will notice that the foliage becomes wilted, yellows and then dies eventually leaving all of the foliage brown, dry and shrivelled. Though fusarium and verticillium may be found in many places and environments, development of the disease is favoured by high temperatures (20-30 degrees) and warm moist soils.

Trying a new pot with new soil is the best strategy. You need to makes sure you don’t put new soil in the old pot, or the old soil in a new pot. Start with everything all new, and also wash all of your garden tools. Using a hand spade in infected soil will transfer the fungus to the new pot, and anywhere else around the garden. Now that these aspects are taken care of, and you are still having problems then what could be causing it?

Plants in poorly drained soil are more susceptible to infection than those in well-drained soil. Wet soil allows the fungus to multiply rapidly and move up through the xylem (the plant’s water-conducting tissue).Infection occurs when the fungus enters the root hair after which it spreads rapidly up the xylem, with the result that it restricts the normal upwards movement of water and nutrients. The fungus produces a toxin that contributes to the wilting and spotting of the leaves.

A definite diagnosis involves making a vertical cut of the main stem just above the soil line. To confirm infection you will observe a brown colour in the conducting tissues under the bark. This discoloration can be traced upwards as well as downwards into the roots. In contrast to fusarium wilt, verticillium wilt discoloration rarely extends more than 25 centimetres above the soil line, even though its toxins may progress further.

Fusarium and verticillum wilt affects 200+ plant species, but in particular tomatoes, chillis, cucumber, potatoes, eggplant, and strawberries. Corn, cereals and grasses are resistant. Its wide host range allows it to remain in the soil for very long periods, possibly several years. It stays alive for long periods of time by living on the dying underground parts of infected plants and can attack and multiply in a number of common weeds, which is just another reason for you to keep the garden bed weeded.

There are steps that you can take to try and control the fungus, but the easiest strategy for now would be to start your tomatoes over in new pots and use new uncontaminated soil, that obviously doesn’t come from the affected garden beds. Remove all of the plants that are affected by the disease and either burn them and throw them in the rubbish, but definitely don’t dispose of them in your compost.
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Fusarium and verticillium wilt thrive in moist conditions, and once the fungus is present in the soil it could take years to eradicate it. Some gardeners try to kill the fungus through a process called solarisation, which involves removing the affected plants, and covering the affected plot with thick black plastic sheeting for 2-3 months, though this is not guaranteed to kill the fungus which is most vigorous. Others have had success in controlling the condition by continually adding compost to the soil. It’s believed that the organisms in the compost can help to inhibit the growth of the fungus. There is no chemical treatment available. To slow the disease, use fertilizer lower in nitrogen and higher in potassium.

There are further preventative measures that you can take to ensure crop health into the future. First, don’t plant tomatoes (or any other plants of the Solanaecae family – potato, tomato, chilli, cucumber or pepper and eggplant) in the same position for at least three years. This will allow the fungus in the soil to reduce enough (without tomato roots or other Solanaecae family members to feed on) to make it safe to grow there again in the future. Use long crop rotations (3+ years) with nonrelated crops, well-drained soils, and soil moisture kept to the allowable minimum for good growth. Also avoid the use of strawberries which are highly susceptible. Rotate with cereals and grasses wherever possible.

There are varieties of tomato that are resistant to fusarium and verticillum wilt, the seed packet would normally be marked with an F for fusarium, and V for verticillium resistance. Better still look for tomatoes that have VFN on the packet as these tomatoes are resistant to verticillium wilt, fusarium wilt (both of these will take out your whole crop) and nematodes. A full resource list of tomato types and their resistance to certain types of diseases can be found online at http://vegetable mdonline.ppath.cornell.edu/Tables/TomatoTable.html

Important points to remember
– Remove and destroy infested plant material.
– Appropriate fertilization and irrigation, avoid over watering.
– Plant disease resistant tomato varieties, labelled VFN.