Tomatoes can develop a variety of diseases including early blight, late blight, Septoria leaf spot, Anthracnose, and Fusarium and Verticillium wilt. Many of these diseases are caused by moisture on the foliage, soil touching the foliage, poor air circulation, or infected diseased plant material left in the garden beds. The best defense against these diseases is prevention, but there are also some things you can do once disease is present.
- Water the soil and avoid getting moisture on the leaves, especially avoiding splashes off the soil.
- Water early in the day so that any moisture that does get on the leaves can dry more quickly.
- Keep leaves from touching the soil through staking, caging, and/or mulching.
- Rotate tomato plants by planting in a different area at least every two years. Once a disease is present, avoid planting in that bed for 2-3 years.
- Remove all dead and diseased plant material throughout the growing season and at the end of the season. Dispose of diseased material and do not place in compost pile.
- Weed around plants to promote air circulation.
- To properly identify a disease, check the UW Plant Disease Diagnostic Clinic website for information or to submit a sample.
- Remove diseased leaves and dead plant material, and in some cases, the entire infected plant
- Spray with Bonide Copper Fungicide or Bonide Tomato and Vegetable 3 in 1, depending on the disease present.
Blossom End Rot
Blossom End Rot is a disorder that occurs on the fruit, creating a brown spot at the blossom end. The spot enlarges to cover the bottom portion of the tomato, where the tissue shrinks and becomes tough. It’s usually caused by uneven watering, a calcium deficiency, or too much nitrogen through over-fertilizing, so be careful not to fertilize too much or too often.
Oftentimes, maintaining even soil moisture through proper watering and mulching is enough to prevent or remedy the issue. You can also add calcium by applying Espoma Tomato-tone, or by adding ground up eggshells to the soil before planting. Calcium can also be applied with a spray solution called Bonide Rot-Stop, which can also be used on other vegetables that sometimes have the same issue.
Failure to Set Fruit
Tomatoes can fail to set fruit due to a any number of factors. It can be caused by lack of pollination, too much nitrogen fertilizer, extended periods of cloudy weather, nighttime temperatures under 50 degrees or over 70 degrees, or irregular watering. Try using Bonide Tomato & Blossom Set Spray, or hand pollinating with a soft bristled paintbrush.
Sunscald can occur when immature fruits are exposed to direct sunlight, causing discoloration. Plants usually grow so the fruits are somewhat covered by leaves, so do not remove leaves that protect fruit from direct sun.
Fruit Skin Cracking
Fruit skin cracking is generally caused by a shortage of water while the fruit was developing, followed by excess water as the fruit is ripening. Try keeping the plant moderately watered, neither too dry or too soggy.
Catfacing is a large fruit browning and deformity, generally caused by cool temperature when the flowers are pollinating. The best way to avoid this problem is by planting tomatoes later in the season.
Herbicides can drift, causing damage to tomato plants that may resemble a disease with stunted or distorted leaves. Drift can occur up to a half mile from the source in agricultural fields or from neighboring yards. Avoid spraying broadleaf weeds around tomatoes and only spray herbicides when there is no wind.
Large caterpillars of the hawk moth that can cause great damage to tomato leaves if unchecked. It’s best to pick off and dispose of the caterpillars, or for a large infestation spray a Bt spray such as Bonide Thuricide (Bt) or Bonide Captain Jack’s Deadbug Brew.