Tackling tomato troubles

The most phone calls I receive from homeowners are for three issues. One is lawn care – people who are unhappy with the condition of their grass. Two is weeds – often connected with number one. Three: tomatoes. It’s that time of year again, when the phone calls and the plant samples start rolling into the office, to get help with dying tomato plants.

Without a doubt, for many gardeners growing great tomatoes in the summer is an annual goal. “This is the year,” is the internal dialogue, “I’m going to grow the BEST tomatoes!”.

I get many, many calls from frantic and sad gardeners asking me to help save their tomato plant(s) from eminent 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, Early blight, Septoria Leaf Spot, Fusarium and Verticillium Wilts, all of which are fungal diseases. There are bacterial Spot and Speck, caused by bacteria, as the name suggests. These are just a few of the problematic disease tomatoes are vulnerable to. Then there’s Blossom End Rot, which is an “abiotic” disease, meaning it’s not caused by a living organism.

Don’t even get me started on insect pests! The diseases that cause leaf spots (which includes the blights, the spots and the specks) are driven by the presence of the disease inoculum (the pathogen, whether fungal or bacteria), plus splashing water (rain or irrigation) and warm temperatures. To help prevent the spread of disease, it helps to mulch your plants, which prevents soil – with disease inoculum – from splashing onto plants, infecting them, stake them so leaves are above the soil, and then ensure plants are as healthy as possible by liming and fertilizing correctly.

Controlling diseases requires spraying as soon as possible in the disease cycle. Generally speaking, sprays man prevent diseases from becoming established but cannot cure existing diseases. For fungal diseases, using a fungicide (labeled for tomatoes) that contains the active ingredient chlorothalonil can help prevent the spread of disease.

If the problem is a bacterial disease, a fungicide will not be effective. Using a copper based spray for bacterial spot and speck may help manage the disease if applied timely. Often it is hard to tell what is causing the leaf spot, whether a fungus or bacteria, or a plant may have more than one disease, adding to the confusion. If using a copper spray, use with care as copper may damage leaves under certain conditions.

The Wilts (Fusarium and Verticillium) are fungal diseases which can be devastating: 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 or Big Beef, to name a few. 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 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 common 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. Low soil pH may 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 and high temperatures and/or irregular soil moisture (dry/wet periods) make it even more difficult for calcium to move through the plant. We can’t do about temperature, but we can ensure good soil moisture by watering regularly and sufficiently. There are foliar sprays that claim to help with BER, however research has shown that while calcium is taken up by the leaves it is not transported to the fruit, and such sprays are not effective in managing the disorder.