Growing your own tomatoes means you get to customise their delicious flavours – and reap the enormous satisfaction of watching them grow into big, juicy baubles. But you’re up against competition – tomato plant diseases such as fungal, viral and bacterial diseases.
1. Septoria Leaf Spot
This is one of the most common tomato leaf diseases, caused by your patch being overcrowded meaning poor air circulation. As well, the fungus is given the ability to thrive if you water the plant instead of the soil, allowing water to linger on leaves. It appears during warm, wet weather as small spots with reddy-brown margins and lighter coloured centres. These spots can join up and form large blotches. The spots first appear on the lower leaves and spread up the plant and, if left untreated, causes leaves to yellow and wilt. If you get in early, you can treat it with an organic copper-based fungicide. Otherwise, remove the plant and destroy it. Don’t grow tomatoes in the same spot for the next 3-4 years.
2. Anthracnose
Basically this is fruit rot, where the fungus causes round, sunken lesions on both green and mature fruit. As the disease progresses, the lesions get larger, deeper and darker. The flesh may rot completely through, especially on overripe tomatoes. It thrives in old plant debris, but it can also be contained in seeds. Watering the plant rather than the soil means water lingers on the leaves and encourages the disease, especially in warm, wet weather. It’s very contagious and it’s best to remove infected fruit immediately. Treat plant with an organic copper-based fungicide. Wear protective gear such as gloves and goggles, follow label instructions carefully and apply only as needed.
3. Fusarium and Verticillium Wilt
The fungi that causes these two wilting diseases enter the plant through the roots, then move up the plant’s vascular system. The lower leaves begin to go brown, wilt, then die and the disease continues to spread up the plant. Salvage any fruit you can then pull out the plant and destroy it (though not in your compost). As the fungi remains in the soil for many years, grow future tomatoes in a container with sterile potting mix. Or, if you have the time, cover the soil with black plastic for 10 weeks – the heat build up will destroy the fungus. Heirloom tomatoes are most susceptible to attack.
4. Early Blight
The fruit is set, the weather is warm and the humidity is high – that’s when early blight hits and ruins your crop. Caused by the fungus Alternaria, the spores settle on older leaves, creating ugly brown or black markings, and the stem ends of the fruit, creating large, depressed black sores. Fortunately, it doesn’t kill your plant, just reduces your yield. Remove infected fruit and leaves and put in the rubbish, not the compost. Prevent it occurring by not overcrowding your patch and allowing for plenty of air movement. Treat it with a fungicide – you can make your own with a solution of equal parts water and milk, or three teaspoons of bicarbonate of soda in a litre of water with a dash of fish emulsion.
5. Mosaic Virus
Plant debris is the most common form of infection, but it can also come from other plants, insects (aphids, whiteflies and thrips) and infected seeds. It’s very contagious and can linger in the soil for two years, entering the plant through small wounds caused by chewing insects, pruning or even by a hand that picks up the virus from the soil. Once infected, leaves become mottled with pale yellow patches. Fruit set is significantly reduced and those that do mature can be dotted with yellow spots and the flesh inside is brown. There’s no treatment for this virus, so the plant should be removed and destroyed – don’t put it in your compost. Prevention is the best option by making sure your tools are always clean and sharp.
6. Bacteria
The most common bacterial tomato diseases are bacterial spot, bacterial speck and bacterial canker, all of which appear as spots on leaves and fruit, even though they are quite different. The bacteria enter any small flesh openings so avoid pruning or wounding the plant with ties. They mostly affect heirloom tomatoes that haven’t been bred for disease resistance. Treat immediately with an organic copper spray and don’t plant in the same spot or where you’ve been growing peppers or capsicums for 3-4 years.
Preventing tomato diseases is better than the cure
The most common tomato diseases are fungal and it’s so easy to prevent. Here are 4 ways you can garden better and have the best tasting salads or pasta in your neighbourhood!
- Don’t overcrowd your plants. Tomatoes need lots of air circulation and overcrowding gets in the way of air movement.
- Don’t water the plant – water the soil! Water resting on tomato leaves is a leading contributor to fungal diseases.
- Trim the lower branches and leaves of the plant so they are not sitting on the soil.
- Keep your garden tools clean.
