Velvet spot disease is widespread and only affects greenhouse tomatoes. You can prevent the fungal disease with a few simple measures.
Velvet spot (Cladosporium fulvum) only affects greenhouse tomatoes. The disease is favored by heat and high humidity. Not all varieties are affected, but the disease is on the rise and is spreading. Only the leaves are affected. The fruits remain intact and can be harvested and used as usual.
Infestation was first detected in 1883 on tomato plants from South Carolina. South America, the original home of the tomato, is believed to be the place of origin of the fungus.
Detect velvet spot disease
The first signs of velvet blotch become visible at the earliest one week after infection. Greenish or yellowish spots form on the leaves of the tomato plant. At a humidity of 90 percent and more, the disease can spread within a few hours. As the infestation progresses, the leaf spots fuse together and the leaves die.
The undersides of the leaves are covered with a whitish lawn of fungi. In an advanced stage, the mold turns brownish. The spores are spread further via this fungal covering. They can survive for up to a year and defy cold and drought. The fungal spores are spread by water and wind.
Tip: In the greenhouse, it is also possible for contaminated tools to spread.
Fighting Velvet Blotch
In order to be able to combat the infestation in the long term, tomatoes in the greenhouse must be checked regularly for possible damage. Infested plant parts must be disposed of completely and do not belong in the compost.
Tip: The fungus could survive in the greenhouse and damage the young plants next spring. If young plants are attacked, this also affects the later yield.
Biological agents or household remedies for pest control have so far remained ineffective. For combat is a suitablefungicide needed. Preparations with the active ingredient azoxistrobin have proven themselves. The fungicide penetrates the leaves and fights the fungus at its roots. In order to be able to combat the velvet spot disease completely, the spraying should be repeated after about ten days.
Prevent velvet spot disease
1. Decrease Humidity
You can prevent the fungus from appearing if you permanently reduce the humidity in the greenhouse to less than 85 percent. Avoid watering the tomato plants through the leaves to prevent leaf wetness. It is better to choose a suitable irrigation system that supplies the plants with water from below. Drip irrigation has proven itself. Since only a small amount of liquid is used, only small amounts of water evaporate and the humidity can be kept low.
By applying a layer of mulch, you reduce the frequency of watering. However, you cannot pour the irrigation water directly onto the mulch layer. Watering is therefore more complex, because you have to remove the layer of leaves first.
2. Ensure adequate ventilationIn order for the air in the greenhouse to circulate well, you have to ventilate it frequently. It is therefore an advantage if the greenhouse has sufficient ventilation flaps. Alternatively, fans can be used.
When planting, make sure that the tomato plants are not too close together. In dense stands, the velvet spot disease multiplies extremely quickly. A planting distance of at least 70 centimeters prevents moisture from accumulating between the plants. Regular pinching of side shoots counteracts leaf density.
Tip: Remove the lower leaves for better air circulation between the plants.
3. Choose robust tomato varieties
If you decide to buy resistant tomato varieties, you can specifically counteract an infestation. However, the market situation is somewhat confusing.
In recent years, the infestation has increased significantly, especially in organic horticulture. There has been increasing success in breeding plants that are resistant to velvet spot disease. However, some of them also became victims of the disease after a short time.
The following tomato varieties are considered resistant to velvet spot disease:
-
- Tomosa
- Vanessa
- Moravi
- Concorde
- Bolzano
- Favorita
- Culina
The Phantasia tomato and the Cherry tomato Philovitaode have proven to be resistant to an infestation. proven.
An overview of the most important preventive measures
| Measure | Explanation |
|---|---|
| Reduce Humidity | Humidity should be constantly between 60 and a maximum of 80 percent |
| Avoid leaf wetness | Do not water tomatoes from above |
| Mulching | if a layer of leaves is brought to the ground, the moisture can stay in the ground longer and less watering is required |
| Airing | Air the greenhouse regularly so that heat and moisture do not build up inside |
| Note the planting distance | at a planting distance of between 60 and 70 centimetres, air circulation is ensured and the fungus can multiply less quickly |
| choose robust varieties | Some varieties are unaffected by velvet spot disease |