NEWBERRY COUNTY — I love a good tomato. On a big juicy burger or, my favorite, the Mater Sammich, with a slathering of mayo (Dukes, of course). We’re now entering Tomato Season, a time of joy but also of tragedy. Tomato plants like to die. They have a death wish. I get many calls from frantic or sad gardeners asking for help to save their tomato plant from eminent demise. Unfortunately, by the time the gardener realizes there’s a problem, it is often too late to save the patient.
There are a myriad of diseases that beset tomatoes: Late blight (which appears early in the season); Early blight (which tends to show up late); Bacterial Spot and Speck, Septoria Leaf Spot, Fusarium and Verticillium Wilts, Tomato Spotted Wilt Virus and Blossom End Rot. These are some of the more commonly found ailments (though not an exhaustive list). Don’t even get me started on insect pests! The diseases that deliver leaf spots (which includes the blights, the spots and the specks) are driven by the presence of the disease inoculum (perhaps found in the soil, or coming in on the plants), plus splashing water (rain or irrigation) and warm temperatures. To help prevent the spread of disease, it helps to mulch the soil, which prevents the splashing of disease inoculum, stake plants so they are above the soil, and ensure they are as healthy as possible by liming and fertilizing correctly.
To make things more complicated, some diseases are fungal and some are bacterial. The Blights and Septoria Leaf spot are caused by different fungal pathogens. Using a fungicide (labeled for tomatoes) that contains the active ingredient chlorothalonil can help prevent the spread of disease. Just as your doctor doesn’t prescribe antibiotics (which attacks bacteria) for a cold (which is caused by a virus), spraying a fungicide on a bacterial disease will not provide a cure. Bacterial Spot and Speck are, as the name implies, caused by bacteria; spraying with a copper based spray may help manage the disease. Often it is hard to tell what is causing the leaf spot, whether a fungus or bacteria, and you can have both at the same time. One of the (very few) benefits of the drought this year is it may be limiting the spread of foliar diseases, which need splashing water to spread (that’s assuming irrigation is being applied through drip rather than a sprinkler).
Which Wilt
The Wilts (Fusarium and Verticillium) are fungal diseases which can be devastating in the garden: leaves turn yellow and plants rapidly wilt and die. These wilts are caused by soil borne pathogens that clog the internal cells of the plant, preventing water uptake. If this has been a past problem, use disease resistant cultivars such as Celebrity, Big Beef, and others. The plant label will have an F and/or V after the name to indicate the variety is resistant to these diseases. Unlike the foliar diseases, which can to some extent be managed with sprays, there is no cure for the wilting diseases, and the plants will die rapidly. Should this happen, don’t plant tomatoes (or anything in the tomato family like Irish potatoes, eggplant, or peppers) in the soil in that area for at least four years, or move to containers. This gives time for the disease pathogen to die in the soil, without a host to support it.
Another common problem is Tomato Spotted Wilt Virus (TSWV). This disease is spread by a very small insect called a thrip – hard to see unless you’re looking closely at the flower, where they often hide. If you have plants where one or two (more, if you’re unlucky) are failing to thrive, TSWV may be the culprit. Afflicted plants are short, often with distorted growing points, dark green and/or have purplish markings on the leaves. Some years are worse than others for TSWV – this year doesn’t seem to be too bad so far. There’s no cure, however buying resistant varieties – look for the TSWV on the plant label – can help if you are regularly plagued with this issue.
One of the most prevalent tomato diseases is Blossom End Rot. BER causes blackened, sunken areas on the fruit, usually at the bottom of the fruit (the “blossom end”), but sometimes on the sides. BER is an “abiotic” disease, meaning it is caused by non-living factors. The basic cause is a lack of calcium. Calcium is an essential plant nutrient that enables plants to build cell walls and tissues. Without calcium, tissues are weak, turn black and die. Most fertilizers have sufficient calcium. If you have limed your soil, that also usually has calcium included. However, calcium is an immobile nutrient – it doesn’t move easily through the plant. High temperatures and/or irregular soil moisture (dry/wet periods) make it even more difficult for calcium to move through the plant. There isn’t much we can do about temperature, but we can take steps to ensure even soil moisture by watering regularly and sufficiently.