Rarely does a tomato growing season go off without a hitch. You’re not the only one in your garden looking for a healthy tomato plant and juicy red fruit. Numerous pests, pathogens and funguses are all looking to benefit from the hard work you’ve put in. But, with each new issue you face you’ll learn a little bit more about your garden and what you can do in the future to be more successful.
Though every situation calls for a different action there is at least one gardening principle you should stick by to maintain a healthy garden: cleanliness. Always remove all disease or pest affected plants either immediately or at the end of the season, never leave them in your garden to compost as this will nearly guarantee you will encounter the same problem next year, and always clean your garden tools after use to prevent the spreading of disease. Below is a list of some of the more common issues you might run into while growing tomatoes. Use the table to try to match up what you see on your tomato plant with the issue most likely causing it and what you can try to do.
| What it looks like: | What it’s called: | What to do about it: |
| Seedlings wilt and die soon after germination. | Damping Off | Damping off can be caused by many pathogens founds in your soil. Make sure to use new or sterilized seed starting mix. Cold and overly moist conditions lead to more occurrences. Start seeds indoors in a warm locations, do not overwater, and once seedlings are established allow soil to dry out between waterings. |
| Fruit with large cracks along the fruit’s skin. | Uneven irrigation, High temperatures |
If the cracks are in concentric circles around the stem, uneven irrigation is to blame. Plants in soil that quickly goes from dry to saturated absorb this moisture into the fruit, causing the cracks. Water less and more evenly. Vertical cracks along the height of the fruit are more likely due to high temperatures. Pick fruit as soon as it’s ripe and in the hottest areas, provide a light shade cloth for your plants. |
| Blossoms Drop Off | Extreme temperatures, lack of sun, young blossoms |
Temperatures below 55 and above 95 degrees will often cause blossoms to drop. Provide shade or cold protection as needed. If plants are in part shade they are most likely not getting enough sun to produce blossoms and fruit. Only plant tomatoes in full sun. The first blossoms of many young tomato plants are often unsuccessful. The next set should do much better. |
| Wilted looking leaves thicken and curl upward. Sometimes remaining green, often yellowed with purple veins. | Curly Top Virus | This virus is spread by the leafhopper, a small ¼ inch insect living throughout the plant. Affected plants should be removed immediately and sealed in a plastic bag to prevent the leafhopper from spreading. Treat neighboring plants with strong water spray to knock off insects, insecticidal soap, or neem oil. Some evidence suggests denser plantings or areas with less bare soil are less desirable to leafhoppers. |
| Light green coloring between veins of young leaves turning into a “mosaic” pattern throughout leaves. Leaves may become wrinkled with new growth becoming stretched out and elongated. | Tobacco Mosaic Virus | The virus is not transmitted from plant to plant by insects, but by direct contact with neighboring plants or indirect contact by the gardener through hands or garden tools. This virus is much less likely to occur in plants started as seeds at home. Store bought transplants are handled much more and are more likely to be affected by the virus. Carefully remove affected plants. Do not handle plants more than necessary. Do not smoke tobacco around plants or before working in the garden. Many hybrid tomato varieties are resistant to TMV. |
| Entire leaves and sections of the plant turning completely yellow. Spreading to and killing entire plant. | Fusarium Wilt | Caused by a soil fungus that can live in the soil for many years. Improve tilth and drainage of poor soils to prevent spreading of the disease. Remove all affected plant material. In heavily affected soils plant resistant varieties. |
| Older and lower leaves begin to turn yellow and die. Entire plants usually are not killed. | Verticillium Wilt | Caused by a soil fungus similar to Fusarium Wilt. Plants usually survive but their production and vigor is greatly reduced. Try not to plant tomatoes in the same area as previous years. In heavily affected soils plant resistant varieties. |
| Light brown or yellowed spots on sides of fruit facing the sun. | Sun Scald | Caused by the fruit being overexposed to the sun. In the hottest months of summer provide shade cloth for your plants. Maintaining a healthy tomato plant with sufficient leaf cover also helps. |
| Small yellow blotches appear on leaves, turning brown. White powder covers affected leaves. | Powdery Mildew | Caused by a fungus most prevalent later in the season. Spreads by wind and direct contact, moving quite easily from plant to plant. The disease will decrease the vigor of the the plant but is usually not severe enough to stop production. Certain organic sulphur based sprays can be effective. |
| Small black or brown spots on leaves, stems and upper portions of fruit. | Early Blight | Caused by a fungus early in the season where cool, humid and rainy weather persists. The disease will stop once temperature increases and humidity decreases. |
| Water-soaked/ oily purple-brown areas on leaves, stems, and upper portions of fruit. Grey fungus on underside of leaves. | Late Blight | Caused by a fungus that favors high humidity and mild temperatures. Avoid overhead irrigation to keep plant material dry, as the the fungus needs moisture to grow. Remove all affected plants immediately. |
| Brown or blackish spots on the bottom (blossom end) of fruit. | Blossom End Rot | Not caused by any pathogen. Typically due to low levels of calcium in the soil or uneven watering. If possible test your soil for calcium levels and fertilize if needed. Apply irrigation evenly. Fruits will still be edible and often times even sweeter than unaffected fruit. |
| Small black or brown slightly sunken water soaked spots on ripe fruit. | Anthracnose | Generally occurs on ripe or overripe fruit in moist conditions. Make sure to pick fruit as soon as it is ripe. Remove any affected fruit immediately. Avoid overhead irrigation or overly moist soils. |
| Younger plants or seedlings have small holes in leaves. Small insects jump from plants when touched. | Flea Beetles | Flea beetles are small (up to ⅛ inch) insect that commonly feeds on tomato and other veggie foliage. Damage to more mature plants is usually insignificant and an otherwise healthy plant will be just fine. Younger plants and seedlings can be protected with row covers. Insecticidal soaps or neem oil can be used in severe cases. |
| Groupings of small grey, yellow or green insects on underside of leaves. Leaves may be yellowed and curled. | Aphids | Aphids are typically an early season pest that dissipate as plants grow larger and the season progresses. Ladybug larvae are a common predatory pest to aphids and can be introduced with store bought ladybugs. Try not to spray insecticides too early in the season to allow beneficial insects to develop. |
| Young plants cut off at the soil line. Fruit touching the ground has tunnels/holes. | Cutworm | Cutworm larvae are what do the damage. Usually growing to 1 to 2 inches long, they are active at night and often curl into a spiral when disturbed. Till your soil at least two weeks before planting your tomato transplants to discourage larvae from staying around. Collars can be placed around young transplants to prevent damage. |
| Leaves, blossoms and fruit eaten with no damage to stems. Large caterpillars and droppings are present. | Hornworm | Hornworms are large green caterpillars with distinctive patterns and large horn on rear end. The caterpillars can easily be hand plucked off the plants and killed. Their small white to light-green eggs are laid one per leaf and should be removed as well. Insecticides are not typically needed. |
| In warmer climates, pin holes appearing in leaves, stems and fruits | Tomato Pinworm | Pinworms propagate very quickly, causing the damage to increase rapidly as the season progresses. Try not to plant tomatoes in same location as previous years. Clean up all infested foliage well at the end of the season. Insecticides are somewhat effective. Fortunately, affected tomatoes are perfectly safe to eat. |