What’s wrong with my tomatoes?
Even the best-cared-for tomato plants can be plagued by problems once in a while. Diagnosing the culprit is the first step to a solution. Here are six common tomato plant problems that can crop up and what you can do to help avoid them in the future.
Blossom end rot
When the bottom of a tomato blackens into a sunken, ugly, leathery spot, you’re looking at blossom end rot. It’s caused by insufficient calcium levels in developing fruit due to a lack of water, which prevents plants from taking in calcium. You can eat the fruit but may have to cut off a good portion of it.
What to do about blossom end rot
- Water regularly and use a fertilizer that contains calcium.
- Apply a couple of inches of organic mulch to keep the soil evenly moist during the growing season.
- If it's still a problem check the soil's pH — a range of 6.5 to 7 is best. Too high or low and blossom end rot may crop up.
If you go out to harvest your tomatoes and see a black hole near the base of the fruit stem, that's a sign that tomato fruitworms (Helicoverpa zea) are around. Cut the tomato open and you'll see tunnels — you might even find the culprit there, too. Tomato fruitworm is a 1 ½- to 2-inch long caterpillar that varies in color, so you'll see it in light green to brown or black with stripes running the length of its body. Once mature, the larva drops to the soil to pupate and in a couple of weeks emerges as a yellow-tan moth that starts the life cycle all over again by laying eggs on tomato foliage. The fruit is usually a mess once fruitworms have been visiting so you won't want to eat it.
What to do about tomato fruitworm
- Interrupt the life cycle of tomato fruitworm by collecting infested fruit before the caterpillar emerges and sending it away in the trash.
- Till the soil in fall to try and expose overwintering pupae.
- Try Bt (Bacillus thuringiensis). It's an organic pesticide that's fatal to caterpillars and is safe to use on edibles. Just be sure to wash fruit thoroughly before eating. However, Bt can also kill butterfly larva so use it sparingly if you know you have desirable caterpillars, as well.
In early to midsummer, these big (up to 4 inches long!) caterpillars can quickly strip a plant of foliage and may sometimes even chew on green tomatoes. Small tobacco hornworms (Manduca sexta) are plain yellow or white with no markings. They gradually turn green, develop white stripes and the namesake "horn" on the last abdominal segment as they mature. Tobacco hornworms are the larvae of the sphinx moth.
What to do about tobacco hornworms
- If numbers are small, handpick caterpillars and drop them in soapy water to kill them.
- Grow sweet alyssum (Lobularia maritima), dill (Anethum graveolens) or Shasta daisy (Leucanthemum x superbum) to attract braconid wasps, which lay eggs on the tomato hornworm, parasitizing and killing it.
- Bt is also effective. Thuricide®, which contains the kurstaki strain of Bacillus thuringiensis, works well on tobacco hornworm and is safe to spray right up to harvest, but be sure to wash fruit well before eating it.
Cracking or splitting
When dry weather gives way to a rainy period or you've watered sporadically, cracks or splits show up in tomatoes — the sudden increase in water uptake by the plant makes the skin split. The tomatoes don't look good, but you can still eat them.
What to do about cracking and splitting
Tomatoes do best with 1 to 1½ inches of water a week. You can avoid cracked and split fruit by watering plants regularly throughout the growing season and applying an inch or two of organic mulch, such as straw or bark chips, to conserve water.
Late in the growing season you may come across tomatoes that look like this one. It's caused by stinkbugs feeding on the fruit. The spots are soft and spongy but superficial so you can still eat the tomato.
What to do about cloudy spot
Are there weeds growing near your tomatoes? That's usually where these pests make their home so if you get rid of the weeds, the stinkbugs will likely relocate and leave your tomatoes alone.
This unusual-looking condition happens when flowers don’t develop properly. It’s usually caused by low nighttime temperatures (below 55 degrees) or strong winds. Catfaced tomatoes may look deformed, but they are still OK to eat.
What to do about catfacing
Shelter plants from strong winds and protect them from low temperatures by covering them at night with row cover or an old sheet.