Anyone who knows the taste of a freshly harvested tomato from their own garden will never want to eat other tomatoes again. In principle, the plants are easy to care for and promise a rich harvest. In some years, however, this does not work at all. Instead, within a few days, the leaves and fruits of one or more plants will turn brown. They fall off and there is no harvest.
Late Blight - Emergence
What causes late blight in tomatoes?
Late blight is an infection with the fungus Phytophthora infestans. In order for this fungus to be able to spread, two factors are needed above all: the fungus or its spores must be present and your tomato plant must be exposed to moisture for a longer period of time. In addition, medium temperatures of around 15 °C are helpful. Dry, warm summer weather with temperatures of 20 °C and more gives late blight no chance.
Development of late blight/brown rot on tomatoes
potato plants
Incidentally, the fungus also feels at home on potato plants or seed potatoes. A potato field next to your garden is therefore definitely a risk of disease. The spores can be carried by the wind from potatoes to tomato plants if they are too close together. Infection through tools, buckets, soil or trellis is also quite possible.
damage picture
What does brown rot on tomato plants look like?
The first signs of disease are brown spots, which usually appear first on the leaves but can also appear on the stems. In a short time, the leaves turn black, curl up, and then fall off. Then the tomatoes also get brown to blackish spots. They become hard and inedible due to the fungal attack. Both ripe and unripe fruits are affected. Since brown rot spreads very quickly, you should fight the fungus as quickly and radically as possible.
Tomato plant with mottled leaves
Happen
When and/or where does late blight occur most frequently?
Like most mushrooms, the Phytophthora infestans loves a humid climate. Therefore, it occurs mainly in rainy summers. Temperatures of around 15 °C and occasional drizzle are ideal for the spread of Phytophthora infestans, i.e. a typical northern German summer. Outdoor tomatoes are affected more often or more severely than plants in greenhouses. But even there, their tomato plants are not really safe from the fungus. In dense plantings, the fungus can spread particularly quickly from one plant to the next.
Tomato mixed culture in the garden
Requirements for a good tomato harvest:
- warmth
- Sun
- dry air or dry leaves
- pour copiously
combat
How can I safely combat late blight?
If your tomatoes are already infested, then late blight can hardly be combated. Your only chance is to discover the infestation at an early stage and immediately and radically remove all infected parts of the plant. However, do not dispose of the clippings in your compost, as you will never get rid of the fungus. He winters there very well. Spread the mature compost later in your garden at some point, spreading the fungal spores all over the place. As soon as you plant potatoes or tomatoes, the fungus spreads further and you have to fight it again.
prevention
How can I prevent late blight?
It is much easier to prevent late blight than to fight it. The most important preventive measures against late blight include sun and wind. Both prevent the tomato leaves from staying wet for a long time after a rain shower. Unfortunately, both are little to influence by the gardener. However, you can choose an appropriate location for your tomato plants: sunny and not sheltered from the wind. With a roof you can also protect the plants from rain. Loose soil prevents waterlogging. A minimum distance of about 50 to 70 centimeters between the individual plants helps to prevent the plants from touching and infecting each other.
control
Check your tomatoes regularly so that they can react in good time to any fungal infestation. You can start with the young plants, but no later than June. Remove the lower leaves of the plants up to the first shoot, where fruit clusters form. This reduces the risk of fungal infestation and the spread of spores through the irrigation water. As a precaution, you can dust the tomato plants with non-toxic algae lime or rock dust, which protects the leaves from the penetration of fungal spores and reduces moisture.
Algae lime as an ecological fertilizer
field horsetail
A few times a week spray your tomato plants with a chilled horsetail tea. To do this, pour about a liter of boiling water over five grams of dried field horsetail. Let the tea steep for five to ten minutes and then strain it. Alternatively, you can use a tea bag. If you want to use fresh field horsetail, you need about 100 to 150 grams for one liter of tea. The tea must only be sprayed when it is completely cool, otherwise your tomato plant will suffer burns. Stop spraying the plant a few days beforehand so that the taste of the horsetail does not transfer to the harvested fruit.
watering rules
Do I have to pay attention to something when watering my tomato plants?
The spores of Phytophthora infestans are not only spread by wind but also by water, for example by rain but also by improper watering. It is best to use low-lime water to water your tomato plants, preferably from a rain barrel. Water directly to the roots of each plant with a soft stream. The less water hitting the leaves, the better.
Resistant Varieties
Are there brown rot resistant varieties?
Since late blight can quickly become a problem and, in the worst case, threaten the entire crop, breeders have developed resistant varieties. Unfortunately, these are not completely resistant either. With good care, however, you have a real chance of getting a bountiful tomato crop despite the inclement weather, without having to constantly fight fungal infections or other diseases. Inquire about resistant varieties when purchasing your young plants or seeds.
protective measures
How do I protect my tomatoes from reinfestation?
If you've ever had to deal with brown rot, you should do everything you can to protect your tomatoes from it in the future. This applies not only to the plants of the current year, but especially to the years to come. Disinfect any tools that may have come into contact with the fungal spores. Likewise, treat buckets and climbing aids if you have used them. You do not need a special disinfectant for this, boiling water is sufficient. If available, you can also use a gas burner for this. However, caution is required.
Tomatoes as a mixed culture
relocation
Plant your tomatoes in a different spot next year. This should be as far away as possible from last year's location where your tomatoes with late blight were. Equally important is the distance from areas where you planted potatoes last year, because the soil here could also be infected with brown rot.
Glasshouse
If you live in an area with occasionally wet and/or cool summers, it is best to plant your tomatoes in a greenhouse, where the risk of late blight infestation is significantly lower. Replace the soil as a precaution every spring. Also remember clean tools (spade, wheelbarrow, shovel, etc.). If you don't have a greenhouse, build a small roof over your tomato plants. This offers at least minimal protection against fungal spores and can also be built quickly if a longer rainy period is announced.