2009-09-03 / News

Backyard tomato troubles

The Island Garden
By Roger Marshall

We talked about tomato late blight a few weeks ago, but lately, I’ve been getting a lot of questions about other tomato problems. Most of the questions are about disease, but one or two have been rather intriguing and I thought they’d be worth a mention.

One gardener asked why her tomatoes had crumpled leaves and dark green areas on the foliage, but otherwise, the plants were fine. After a lot of perusing of gardening books, I found the only thing that looked like the symptoms she described was cucumber mosaic virus. When I later saw that the plants were next to the cucumbers and other squash, it seemed the likely culprit.

Smokers can transmit tobacco mosaic virus to their tomato plants. Smoking and then handling the plants, or picking tomatoes while smoking, can transmit the disease, which shows up as yellow, brown or dark green spots on the leaves, depending on what strain of virus the plant has. Feeding the plant with a good tomato fertilizer will usually save a good crop, but the plants can die. Any infected plants should be thrown in the trash rather than put in the compost pile as some viruses can survive the heat of the compost pile.

Another gardener had perfectly tasty tomatoes, but with green shoulders. This condition is known as greenback or green shoulders, and can be caused by either a lack of potash in the soil or too high a temperature in the greenhouse before the plants were sold to unsuspecting buyers. There is not much you can do about high temperatures, except hope that it is a lack of potash and dig some into your soil this fall.

Blossom end rot is another tomato disease that is often seen on the first tomatoes on the vine. There’s not much of that around this year because we’ve had so much rain. It is caused by irregular watering while the plant is growing. If you’ve seen it on your plants in past years, make sure you water them regularly until after they set fruit. Usually, blossom end rot shows up on the first tomatoes on the vine and doesn’t appear again. Infected tomatoes should be thrown out, as the rot usually goes well into the core.

If you see a totally stripped top portion of a plant with its leafy matter missing, look for a large, green-striped caterpillar with what appears to be a horn on one end. This caterpillar, the tomato hornworm, grows from three to five inches long and can trash a plant in almost no time. It also likes other plants, such as potatoes, peppers and eggplants. Control the insect by picking the caterpillars or by spraying the plant with Bacillus Thuringiensis (BT).

Though it’s a nuisance, there’s a slight dichotomy about this insect. The moth looks like a hummingbird moth and is often attracted to buddleia and other plants that attract hummingbirds. So you can put up with the caterpillar (move it to another plant some distance from your tomatoes) and enjoy the moths, or eliminate the caterpillar and have no moths.

If you see a tomato hornworm with what looks like dozens of egg cases on its back, leave it. It is being attacked by a parasitic wasp and will die soon. The wasp eggs will hatch and leave the dead caterpillar to look for other hornworm caterpillars.

I don’t know about you, but I find it fascinating to understand how nature controls insects and parasites. The hornworm caterpillar is a good example. While we enjoy seeing the moths flitting around the buddleia, we don’t want the caterpillars on our garden plants. Nature, in its own way, says, “That’s OK, neither do I,” and uses a tiny wasp to keep the hornworm population in check.

By understanding how nature works, you can often use natural controls to avoid spraying pesticides in your garden.

Return to top