The Great Tomato Challenge

John Wilson

Over the years, I’ve observed an informal competition between gardeners to see who can produce the first ripe tomato. I’ve actually had people stop me in the post office or grocery store to tell me how close they were to having that first tomato… or first BLT sandwich! Their “green thumb” efforts are being challenged again this year by Mother Nature.

We’ve had a lot of rain and driving winds, perfect conditions for early blight to develop. Early blight usually starts on the lowest leaves and gradually moves up the plant. Once a leaf is infected, you cannot cure it, but you can prevent it from spreading to other parts of the plant with a fungicide labeled for use in the garden. You will need to repeat these applications every 10 to 14 days… or more frequently if it rains… to protect the new growth. Always observe the waiting period between a fungicide application and when you can safely harvest and eat your tomatoes.

Other things you can do to help prevent the disease this summer is to mulch your tomatoes if you haven’t done so already. In addition to helping keep a more constant moisture level in the soil and preventing the soil from getting too hot around the roots which injures them, mulching also reduces the likelihood of soil particles containing this disease from splashing onto the leaves.

That leads to the second thing you can do to help prevent this disease… always water tomatoes at the base of the plant, not with a sprinkler. A sprinkler, or rain, splashes soil on the plant… and they also keep the foliage wet. The disease needs moisture on the leaf surface for the spore to germinate and infect the leaf. You can’t control the rain, but don’t add to the problem with overhead irrigation.

Staking or caging tomatoes will help reduce the severity of this disease because it keeps the plants upright and promotes better air circulation which causes the foliage to dry faster which reduces the possibility of infection occurring. It also prevents the fruit from coming in contact with the soil which may lead to blemishes or decay… and it makes harvest much easier.

To prevent this disease in future years, clean up all plant debris from tomatoes, potatoes, peppers and eggplant this fall and remove it… because the same disease can infect all four of these plants. Don’t put this plant material in your compost pile or till it into the soil. The disease overwinters on plant debris and could infect these plants next year. Also rotate where you plant these in your garden so you don’t plant any of them in an area next year where any were planted this year.

One other thing that occasionally foils competitors in the great tomato challenge is when they fertilize their plants, particularly with a nitrogen fertilizer. It’s almost amusing (to me, not to them) when someone calls in and asks why their dark green, healthy looking, six foot tall tomato plants are not putting on any tomatoes. These calls usually come with a statement like, “These are the best looking tomato plants I’ve ever grown… and they aren’t setting any tomatoes!”

Tomatoes like nitrogen fertilizer and applying it early will promote these monster plants… BUT… nitrogen fertilizer also keeps plants in a vegetative state (growing leaves and stems) rather than letting them transition to a reproductive state (setting on fruit). Delay fertilizing your tomatoes until they have already set on a couple tomatoes that are the size of a marble. Then fertilize in moderation because overfertilizing is one of several factors that contributes to blossom end rot. We’ll talk more about blossom end rot another day as tomato harvest draws nearer.

For more information on disease control in tomatoes, or other vegetables in your garden, contact your local UNL Extension office.