Tomatoes are a garden staple, but sometimes pests or disease can make growing them a bit more of a challenge. With some tips for prevention and a watchful eye you can identify and eliminate any issues that arise right away, which is the most effective time to take action.
6 Essential Steps for Prevention
Prevention is the key to a healthy garden. Follow these steps to prevent pests and disease.
- Water the soil, not the leaves of a plant, and try to prevent splashing. Wet leaves can promote fungus, and soil splashed onto leaves can spreads soil-born diseases.
- Scout plants regularly, every 7 to 10 days. Look for eggs, insects (friends and foes), and signs of disease (like brown spots on the leaves). Take immediate action if a pest or disease is present. Treating early is always most effective and in the case of pest eggs, it is also more efficient (they aren't mobile).
- Avoid stressing plants (e.g., drought, over/under fertilization, transplanting without hardening off) as it is an open invitation for pests and disease.
- Season-long clean-up. Remove any diseased plants to avoid the spread of disease, and keep the garden weeded as weeds may carry diseases that are spread by insects or contact. Do not compost diseased plant material, as it can persist.
- Rotate tomatoes and other crops (e.g., peppers, eggplant, potato) in the tomato family (Solanaceae), so that they are not grown in the same area more than one time in three years.
- Clean up the garden at the end of the season to prevent pests and disease from overwintering on plant debris.
Diseases are often caused by fungus or bacteria. Once a plant has a disease you can generally only manage the spread of the disease, making early identification and treatment so important. Most fungal or bacterial diseases can be organically treated using copper or sulfur. If you must treat for insects, apply organic pesticides in the evening, night, or early morning and avoid applying it to flowers. These practices help keep your garden safe for pollinators.
Blossom end rot is a common but fixable tomato problem. The most obvious symptom is a dark area at the blossom end (bottom) of the tomato, resulting from a lack of calcium in the fruit. The main cause is usually not a calcium deficiency in the soil, but drought stress followed by excessive moisture; this fluctuation reduces the plant's uptake of calcium. Avoid blossom end rot by watering deeply on a regular basis, and mulching after the weather warms up and plants are well established.
Tomato hornworms are green, thumb-sized caterpillars that bore into fruit and strip away foliage leaving just the middle vein. Tomato hornworm can be organically controlled using Bacillus thuringiensis (Bt) or spinosad and/or hand picking. Bt and spinosad kill all types of caterpillars; so avoid spraying unaffected plants or butterfly host-plants.
Flea beetles are tiny, hopping pests that chew small holes in leaves and rapidly skeletonize the leaves, especially in spring when they are most active. They eat a number of crops, but prefer eggplant, tomatoes, and brassicas (alyssum, mustard, broccoli, cauliflower, kale, cabbage, radishes, etc.). Organic controls include: row covers installed immediately at transplanting or sowing which protect young plants, frequent applications of garlic or hot pepper spray, or kaolin clay spray, organic neem or spinosad-based insecticide, trap crops such as nasturtiums or mustard grown nearby, and fall cleanup/tilling to help reduce their numbers.
Thrips cause tiny, beige stippling on leaves and spots on fruit where they have fed. Thrips also spread disease. Spinosad is an organic control.
Cutworms are larvae of the black cutworm moth which feed on stems of vegetable and flower seedlings at night, severing the plants at ground level. During the day, they rest just below the soil surface, curled beside plant stems. As there is usually one generation per year, peak damage tends to occur in the spring; setting out transplants later in the season could avoid damage. Protect transplants with collars made of paper, foil, cardboard, plastic, or tin cans with both ends removed; push collar an inch into soil. A week before planting, scatter moist bran mixed with Bacillus thuringiensis var. kurstaki (Btk) and molasses over surface of beds, or apply neem or parasitic nematodes to soil.
Aphids are among the most common garden pests. They feed by sucking plant sap, which causes distorted leaves, buds, and flowers, sometimes spreading plant viruses in the process. Aphids excrete a sticky honeydew which attracts ants, and is a host for black, sooty mold. Knock aphids off plants with a strong stream of water-repeat frequently as needed. There are many native predators and parasites that can control aphids; attract them by planting pollen and nectar plants. For heavy outbreaks, spray insecticidal soap, neem, or homemade oil sprays. Oil sprays work by smothering the insects and mites they come in contact with; thus, thorough coverage is important.
If you are unsure of the disease, your local agricultural extension office can help identify a disease with a sample of the infected plant.