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Dear Top Gardening Friends

Checking the e-mailbag and the electronic pile of tweets that we receive here at @Toporganicguru  will show that at this time of year, with the sun shining in most places and big bowls of salad replacing stodgy meals, people are concerned with their tomatoes. We have all planted the seeds in the early spring and then dreamt of plucking bushels of huge fire-engine-red fruit.

However, the path from seed to salad can be a rocky one. The weather. Lack of sunlight. Drought. Bugs, a fascinating topic we will address later in the month (and about which we’d like your thoughts). And, as we will discuss today, wilt.

As much as you might be watering your tomatoes, they may still be thirsting, due to one of the two most prevalent wilt diseases: Fusarium and Verticillium. These fungal diseases live in the soil, enter the tomatoes through the roots, and interfere with the water-conducting tissues of the plant. Even if the rain in your area has been steady, your plants might look like they haven’t had a drink in days.

Fusarium wilt is the more common fungus, and also affects eggplant, peppers and potatoes. It generally occurs in midsummer when air and soil temperatures are high (over 80 F/27C).  Older leaves near the ground will go golden first, and sometimes the yellowing is restricted to one side of the plant. The affected leaves soon wilt and dry up, but they remain attached to the plant. When the younger leaves begin to turn yellow, the plant is on its last legs and there’s no saving it. To be sure of what has happened, you can do an ”autopsy”, cutting through the stem at ground level and looking at the inside. If there is a narrow column of brown between the center and the outer green portion, there is a great chance you are dealing with Fusarium.

Fusarium’s close friend is Verticillium wilt, who likes to ruin your tomatoes earlier in the year when the soil is a bit cooler (55-70 F/13-22 C).  Other plants in the garden that might be affected are  basil, beans, strawberries, peas, and watermelon. The wilt starts as yellow, V-shaped areas that narrow at the leaf margins. These yellow areas grow larger over time, turn brown, and then the leaf drops off. Often although entire branches are infected, surprisingly the diseased plant continues to live, but will be stunted and weak and produce small fruit. After you’ve removed it from the garden, you’ll see that the stem will display the same symptoms as fusarium wilt and it would take a laboratory analysis to tell the difference. If you do get some puny tomatoes, and it is not yet the height of summer, you can make an amateur guess that the culprit is Verticillium.

Both wilts can be introduced into your garden by contaminated seed or infected transplants – do yourself a favour and check the stem of one of any gifted tomato plants. Once in your garden, these fungi can survive in the soil for many years.

The worse news: there is no cure for wilts, only hopeful control. Here are three easy to remember tips:

Sanitation: Remove and destroy diseased plants at the end of the season. Clean stakes, cages, tools and anything that came into contact with the soil or debris in the infected area with hot soapy water. Dig out the soil that was around the roots and replace with fresh.

Rotation: Switch to vegetables or fruits that are not hosts to wilt diseases in place of tomatoes. Move the tomatoes to a new location for four to six years.

Modification: Scientists have been working to breed tomato varieties that have a resistance to wilt diseases. Many tomatoes today will come with a notation in the catalog or on their label such as “VF12.” meaning it’s  resistant to verticillium and fusarium Races 1 and 2. Some suggestions we have received from you are Ferline, Mountain Glory, Amelia, Fantasio F1 and the rather sinister sounding BHN 602. Check your local supplier to see which might suit your garden the best.

We’ll be discussing tomatoes frequently in the next few weeks, so please do email or tweet your comments and suggestions to @toporganicguru or toporganicguru@gmail.com

Love the life you live

Team Arabella

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