Diseases and Prevention
The good news is that simple management practices are usually sufficient to hold back full-blown infections in tomato plants and keep them healthy enough to produce a good crop.
Hopefully, you’ve started the season off right by planting disease-resistant varieties. And hopefully, you’ve followed the instructions on the seed packet and planted seedlings with plenty of space between them (good airflow is key to preventing fungal disease).
- Minimize Irrigation. Tomato plants have surprisingly low water needs and over watering can promote disease. Once the fruit has started to form, water only when the top three inches of soil becomes dry and the leaves look limp in the heat of the day.
2. Water at Ground Level. Little can be done about water that falls from the sky, but don’t add insult to injury by showering your tomatoes with a sprinkler—fungal diseases only spread when the plants are wet. Instead, use drip irrigation or a soaker hose to water at ground level.
3. Water in the Morning. This way, the moisture will evaporate quickly from the surface of soil, giving the roots the water they need, but keeping the humidity down around the plants.
4. Remove Infected Leaves Immediately. Don’t hesitate to clip off leaves as soon as any spots or deformation is apparent—it may save the rest of the plant from succumbing to the disease. Dispose of these clippings far away from your tomato plants.
Now let’s look at some diseases with the prevention in mind.
1. Early Blight
It can affect the foliage, stems and fruit of tomatoes.
Symptoms: Dark spots with concentric rings develop on older leaves first. The surrounding leaf area may turn yellow. Affected leaves may die prematurely, exposing the fruits to sun scald.
Management: Remove affected plants and thoroughly clean fall garden debris. Wet weather and stressed plants increase the likelihood of attack.
2. Gray Leaf Spot
Gray Leaf Spot affects only the leaves of tomatoes, starting with the oldest leaves.
Symptoms: Small, dark spots that can be seen on both the top and bottom surfaces of the leaves.
The spots enlarge and turn a grayish brown. Eventually, the centers of the spots crack and fall out. Surrounding leaf areas will turn yellow and the leaves will dry and drop. Fruit production is inhibited.
Management: Remove all affected plants and fall garden debris. Select resistant varieties.
3. Septoria Leaf Spot
Septoria Leaf Spot is sometimes mistaken for Late Blight.
Symptoms: The papery patches on the leaves develop tiny, dark specks inside them. Older leaves are affected first.
Management: Copper sprays and Serenade are somewhat effective at halting the spread of symptoms.
4. Southern Blight
Southern Blight manifests as a white mold growing on the stem near the soil line.
Symptoms: Dark, round spots will appear on the lower stem and both the outer and inner stem will become discolored. Southern Blight fungus girdles the tomato stem and prevents the plant from taking up water and nutrients. Young plants may collapse at the soil line.
Management: Crop rotation seems to help. There has also been some evidence that extra calcium and the use of fertilizers containing ammonium offer some protection
Anthracnose is a very common fungus that causes tomato fruit to rot.
Symptoms: Small, round, sunken spots appear on the fruit. The spots will increase in size and darken in the center. Several spots may merge as they enlarge. The fungus is often splashed onto the fruit from the soil.
It can also take hold on Early Blight spots or dying leaves. Wet weather encourages the development of Anthracnose. Overripe tomatoes that come in contact with wet soil are especially susceptible.
Management: Copper sprays offer some resistance. Remove the lower 12″ of leaves, to avoid contact with the soil. Don’t water the leaves, just the base of the plant.
6. Bacterial Speck
There are several bacterial problems that affect tomatoes including Bacterial Speck.
Symptoms: Tiny, raised, dark spots, usually with a white border.
Management: Copper fungicide at first signs of symptoms.
7. Blossom End Rot
Blossom End Rot is as good a description as any.
Symptoms: Dark brown/black spots develop at the blossom end of the fruit and enlarge as the fruit rots. Management: Generally attributed to a lack of calcium during fruit set. This could be caused by too much high nitrogen fertilizer or uneven watering, resulting in fluctuations of nutrient availability.
Management: Remove affected fruit and provide regular, deep waterings.
8. Buckeye Rot
Buckeye Rot is more common in Southern states, especially during wet periods.
Symptoms: Buckeye Rot is similar to Blossom End Rot, except on green fruit. On ripened fruit, the rotting area will appear water-soaked, but not dark in color. The rot develops on the area of the fruit that touches the soil. The spot will enlarge and develop concentric rings that resemble a buckeye. The affected area is smooth, distinguishing it from Late Blight, which has a rough surface.
Management: Remove affected fruit and keep future fruits from contact with the soil.
References: modernfarmer, wikipedia, thespruce