Botrytis: Gray Mold Detection, Prevention And Control

Botrytis cinerea is one of the most common plant-damaging fungi. We introduce the annoying fungus and show how to fight it successfully.

Who does not know it, the gray mold lawn on the beloved strawberries? This is mostly caused by Botrytis cinerea, the gray mold. With a little knowledge of the fungus, you can prevent or control the infestation. We’ll show you how to do this so that you can enjoy your plants for a long time to come.

The fungus Botrytis cinerea is a wound and weakness parasite and is extremely adaptable, so it has a strong tendency to develop resistance. It is one of the most difficult pathogens to control and can cause concern for various plants in our garden.

Botrytis cinerea: the life cycle

This fungus belongs to the Ascomycetes class and has a large number of host plants. This class got its name from the shape of its reproductive organs. The hose mushrooms comprise 45,000 different species and are therefore the largest and most important group among the real mushrooms. The Ascomycetes also include the apple scab ( Venturia inaequalis ), ergot ( Secale cornutum ), or the brush mold ( Penicillium ), which is known for the production of antibiotics.

The conidia (asexual fungal spores) form in the rotting areas. The conidia of the gray mold are spread by the wind or spray water and thus infect new plant tissue. The infection occurs with persistent moisture. The infection then spreads through the fruit and the plant. You can then observe the familiar gray mold lawn on strawberries. However, the fruits can also be infected directly.

Botrytis: Detecting, preventing & fighting gray mold

The fungus overwinters on organic material and in spring it starts developing again. Sclerotia are formed as a permanent form, but the fungus can also overwinter as a mycelium on dead plant parts. Sclerotia are hard permanent forms of mushrooms that are very resistant to drought or cold, which means that mushrooms can remain in a dormant state for a long time until optimal conditions are restored for them. The development is started by the damp conditions in spring and with it, the growth of the fungus begins again and with it the formation of new spores.

The development cycle of the gray mold at a glance:

  • In the soil, some sclerotia can survive there for a long time.
  • The fungus can also survive as a mycelium on organic material.
  • It is from these sources that the spores spread and infect our plants.
  • It is spread by the wind or splashing water.
  • A gray fungal lawn forms on the plants, on which spores also form.
  • Humidity and temperatures between 20 and 28 ° C are ideal for gray mold.

Botrytis cinerea: recognizing the damage

As its name suggests, a flat, mouse-gray fungal lawn forms when it is infested with gray mold. This mushroom lawn has a habit of being heavily dusted. The tissue of the plants dies and brown spots also form on leaves and fruits. The fruits look rather glassy at the beginning. So-called ghost spots can appear on tomatoes. This creates a bright center and around this center, with a little distance, a bright ring.

The fungus can appear on all parts of the plant, soft fruits and flowers are particularly likely to be attacked, but shoots and woody parts can also come into contact with gray mold.

Botrytis: Detecting, preventing & fighting gray mold

Particularly susceptible crops are tomatoes, cucumbers, onions, and lettuce. When it comes to berries, the gray mold is particularly interested in strawberries, raspberries, gooseberries, and blackberries and does not stop at our ornamental plants. Roses, tulips, rhododendrons, and hydrangeas are just a few of the affected ornamental plants in our gardens.

Botrytis: Detecting, preventing & fighting gray mold

Fight botrytis successfully and drive away gray mold

There are different approaches to combating gray mold. Here we show you tips and tricks for prevention and various control measures.

Fight Botrytis cinerea: Suitable sprays

Chemical control of Botrytis cinerea is somewhat of a problem. This fungus is extremely adaptable and can develop resistance very quickly. Therefore, you should first apply our preventive and natural control measures before resorting to chemical control. Studies on raspberries from northern Germany show that 100% resistance can develop after just five years.

If you don’t see a way out, the following active ingredients can promise success:

  • Trifloxystrobin
  • Cyprodinil
  • Fludioxonil
  • Ground fungus Gliocladium catenulatum

Caution is always required when using pesticides. Always follow the instructions for use, especially the information on personal safety and dosage.

Fighting Botrytis cinerea: Natural Measures

Some methods against gray mold have also proven themselves naturally. On the one hand, the use of various manure and teas for control and prevention should be mentioned here, since many of these remedies are plant tonic. Healthy and strong plants are not affected by diseases as quickly as plants in a weakened state.

Botrytis: Detecting, preventing & fighting gray mold

For example, horsetail broth can be sprayed on for strengthening. In the case of strawberries, the roots are dipped in horsetail broth before planting, later growth is supported with diluted nettle manure and the plants are defoliated a little if the crop is very dense. Here you can find out more about the horsetail broth and nettle manure.

Botrytis: Detecting, preventing & fighting gray mold

But you must look for a new location for the strawberries after three years at the latest. Since the flowers of the strawberries are attacked, they can be dusted with rock flour to reduce the attack. The rock flour can also be applied to the soil as fertilizer – especially on acidic soils as a soil improvement. But you shouldn’t overdo it with fertilization. A lot of nitrogen can be beneficial for fungal infections, so use it sparingly.

Botrytis: Detecting, preventing & fighting gray mold

The clever way to prevent botrytis

Since the fungus survives the winter on organic material, we already have the first point of attack. Remove dead plant parts, they are full of spores and thus only infect more plants. It is important to have a few sources of infection in the garden as possible.

Dealing with moisture is also particularly important, as Botrytis favors moisture. Therefore, the planting distance between your plants should not be too close. A greater distance promotes good air circulation and promotes faster drying. Varieties that develop smaller leaves also help here, as they dry off faster.

You should also pay special attention to your casting practice. Do not water from above; this will moisten the whole plant and create optimal conditions for a fungal infection. Therefore, it is best to water the plants where they really need moisture – namely on the ground. If you work with irrigation systems, rely on drip irrigation.

Botrytis: Detecting, preventing & fighting gray mold

With strawberries, you should be careful when using a straw. Of course, it is useful if the strawberries are not full of soil, but you should not spread the straw around the strawberry plants from the start. It is enough if you spread it on the ground shortly before or during flowering. Unfortunately, there are no strawberry varieties that are resistant to Botrytis.

Botrytis: Detecting, preventing & fighting gray mold

Make sure you have a crop rotation in your garden and change the location of your ornamental plants regularly. In the vegetable patch, a mixed culture with garlic or onions can have a preventive effect. The mustard oils in these plants work against the fungus. You can also leave the harvest residues of the garlic and onions in the garden and put them in the ground. The mustard oils are effective against various pathogens and pests.

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Botrytis: Detecting, preventing & fighting gray mold

If you own a greenhouse, you should make sure that the humidity is not too high and that no dew forms on the leaves. Regular ventilation or the use of automatic window regulators is particularly important.

A special storage tip: Chill harvested fruits, especially berries, quickly to 0 to 3 ° C. This means that they stay fresh even longer, otherwise potentially infected fruits could cover your entire harvest with the gray lawn of mold. Also, try to handle the fruit as little as possible and not to damage it.

Botrytis: Detecting, preventing & fighting gray mold

Preventing botrytis: once again briefly summarized

  • Remove infected and dead plant parts
  • Larger plant spacing
  • Do not pour from above but close to the ground
  • Do not lay the straw on the ground until the strawberry blossom
  • Crop rotation and relocation
  • Mixed culture with garlic

Tip: To strengthen the plants that are most susceptible to botrytis and make them more resistant, we recommend our Gardender organic tomato fertilizer. This is ideal for vegetables and berries and has a high potassium content.

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