This is the time of year I have come to dread — Tomato season.
Why would a person dread the approach of summer, representing vacations, beach trips, cookouts and all manner of frivolity? Because of tomatoes. Now, I love tomatoes as much as the next person. Eating them on salads, big juicy burgers, and that Southern classic, the ‘mater sammich, with a slathering of mayo (Dukes, of course).
No, the problem I have with tomato season is that tomato plants like to die. They have a deathwish. I get many, many calls from frantic and sad gardeners asking me to help them save their tomato plant from its imminent demise.
Unfortunately, most of the time the answer is the same: By the time the gardener realizes there’s a problem, it is too late to save the patient.
Let us look at the 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 and Blossom End Rot. These are some of the more commonly found ailments (though not an exhaustive list) that afflict tomato plants. 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 (the pathogen in the soil, from last year’s plants, perhaps), plus splashing water (rain or irrigation) and warm temperatures.
To help prevent the spread of disease, it helps to mulch your plants (this prevents soil — with disease inoculum — from splashing onto plants), stake them 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 attack 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, which is why I often have dying tomato plants in my office this time of year.
The wilts (Fusarium and Vertillium) 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) for at least four years. This gives time for the disease pathogen to die in the soil without a host to support it.
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 they are used properly. However, several factors may contribute to BER, even if fertilizer is used.
Our acid soils, if not adequately limed, prevent plants from taking up nutrients even if they are available in the soil. Lime needs to be applied to the soil 4-6 months prior to planting to raise the pH sufficiently. Other factors are heat and water. 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.
The Cooperative Extension office has many resources to help you grow your best tomatoes. Call or stop by our office at 123 Caroline St. to learn more.
Paige Burns is assistant horticulture agent at the N.C. Cooperative Extension’s Richmond County Center. Extension At Your Service appears each Wednesday in the Daily Journal.