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If you have been out and about in your garden you have probably noticed that there are several diseases of plants beginning to rear their ugly heads after our warm, damp weather. I have noticed this weekend that a little blight has started to show up on the bottom leaves of some of my tomato plants. There are several diseases that can attack tomatoes, usually early blight is the leading problem this time of year, along with septoria leaf blight and some of the wilts such as Verticilium and Fusarium. If your tomato plants start to yellow and wilt out of the blue and just up and die chances are you have one of the wilt diseases and actually there is nothing you can do now, the answer to that problem is cultivar selection, that is picking tomato varieties that are resistant to these diseases. For this usually hybrids are the only way to go.
Now, as for the blights or leaf spot diseases there are actually a few things you can do. First of all you need to keep soil from splashing onto the tomato stems and leaves. With all the rain we have had lately there is really only one way to do this, mulch! Whether it is plastic, bark, straw, or even grass clippings mulch will retain moisture, inhibit weed growth, and keep soil from splashing onto the leaves. Many of our tomato diseases over winter in the soil and as soon as they come into contact with tomato tissue they start to grow.
Plant tomato plants where they get good air circulation. Ideally you should be able to walk between plants. This is not always an option when you have limited space however. Some people like to sucker tomatoes, this might help increase air flow, however it will reduce leaf area for shading fruit and decrease the number of tomatoes. I like a big harvest so I let my tomatoes grow as large as they want to. If too much sun shines on a tomato fruit it will sunburn especially in hot dry weather. This doesn’t happen to plants that aren’t suckered!
As soon as you notice a few spots on the leaves of tomatoes pick those leaves off. Many people even pick the oldest lowest leaves off before a problem begins because they are usually going to be the first to develop a problem and these leaves usually aren’t doing much for the plant anyway.
When you water tomatoes don’t overhead water. The longer tomato tissue is wet the more chance there is that a disease can infect the leaves. Many of the fungal diseases need excess water on the leaves to actually start growing. Use soaker hoses under mulch. This will conserve water because there will be less evaporation, it will put the water directly on the roots, and the plants will get water without getting the leaves wet.
The last thing you can do to combat diseases on tomatoes is fungicides. I tell people all that time that fungicides will not keep their tomatoes from getting disease but it will reduce the amount of disease damage and give you healthier productive plants later into the season. However, no matter what you do you will have some if not a lot of disease problems on your tomato plants regardless of what you do. Personally I have found that a few sprays of fungicides allows me to get larger harvests for longer which allows me to have more tomatoes to can and eat! Fungicides for tomatoes are protectant fungicides only; this means that you must spray all surfaces of the tomato plant to reduce the amount of disease pressure. Fungicides labeled for tomatoes include daconil, mancozeb, maneb, and captan. Personally I like the first three more than captan which can cause some foliar burn in hot dry weather.
If you have any questions about tomatoes, give me a call at the extension office at 336-7741.