The tomato, the unofficial emblem of summer, red and juicy, plucked from the vine on a hot July day and eaten like an apple. Who hasn’t stood in the garden with tomato juice running down their chin? What about a tomato sandwich for lunch, on white bread with mayo (we won’t haggle over brands here), and a glass of ice-cold tea, preferably sweet? Sandwiches, salads, soups, sauces, we use tomatoes in a thousand dishes every year.

We also try to grow them, because homegrown is so much better than store-bought, but sometimes the growing is a lot of work, and the harvest isn’t always successful. Every home gardener has faced the despair of sparse flowering, poor fruit set, blossom-end rot, cracking, zippering, catfacing. Then there are viruses, fungi, and insects like the tomato hornworm that can damage the tomato plants and fruit.

A Gloucester resident recently emailed a question to the Extension Office HelpDesk about a failing tomato plant. The photo she sent showed a weak, spindly ...