Rhizoctonia: prevent & combat beet rot

The famous beet rot is just one type of Rhizoctonia. We show how to get the mushroom Rhizoctonia recognize and what can be done about it.

Rhizoctonia not only affects our beets, but also causes damage to many other plants. It is a dreaded casserole disease, which is often called root killer.

Rhizoctonia

The mushroom Rhizoctonia is on everyone's lips when it comes to root and casserole diseases. Below we explain what the fungus is and how to fight and avoid it.

Rhizoctonia: characteristics and distribution

The correct name of this stand mushroom is

Thanatephorus cucumeris – only its asexual or anamorphic form becomes Rhizoctonia called. Among other things, the fungus can trigger late blight, white trotters or potato pox. It is distributed worldwide and is native to the soil. There are a few subgroups of Rhizoctoniasolani, which only occur in certain parts of the world, such as the Philippines, Japan or the USA.

Rhizoctonia can survive on soil organic matter for up to three years. When the soil temperature rises above 15°C, the fungus becomes active and begins to grow. The mycelium then, for example, grows over the beet in the soil and the hyphae penetrate the beet through cracks and injuries. However, Rhizoctonia can also invade the beet directly because it produces enzymes that can dissolve cell walls. Once the fungus has invaded, it spreads throughout the plant.

The onset of the disease is triggered by external factors. The fungus is present in all soils, but warm temperatures and waterlogging promote infestation. Rhizoctonia also very often causes seedling diseases and emergence damage. Favorable conditions for infestation with Rhizoctonia are:

• Waterlogging and high soil moisture
• High temperatures
• heavy soils
• Bad soil structure
• lack of oxygen
• Low pH

Rhizoctonia species and host plants

There isn't just one type of Rhizoctonia, but many different ones, each of which differs in terms of their preferred host plant and their harmful effects. Here is a brief overview of the various Rhizoctonia-Species:

• Rhizoctoniasolani: Often occurs on beets, legumes, cereals, tomatoes, lettuce and potatoes; can survive as mycelium or forms so-called sclerotia, which enable the fungus to survive in the soil; In contrast to other fungi, it does not form any spores
• Rhizoctonia cerealis: Also called the eyespot and occurs on grain
• Rhizoctonia crocorum: Also called the Violet Root Killer and occurs on carrots
• Rhizoctonia carotae: Is a storage rot pathogen in carrots

Recognize Rhizoctonia: damage and symptoms

Rhizoctonia can cause various symptoms, which we briefly describe below. The symptoms differ depending on which culture the fungus occurs on.

Rhizoctonia on turnips

Late beet rot often occurs Rhizoctoniasolani on turnips like Beetroot, chard or sugar beet and causes the beet plants to wilt from the outside in. The leaves then turn yellow and lie on the ground in a wreath around the beet. Dark-brown, dry rotting spots that extend far into the beet also appear on the beets. Even if the beet has already died, it will continue to shrink.

Rhizoctonia of potatoes

also on potatoes some symptoms can develop when Rhizoctoniasolani are affected. For example, dark brown to black potato pocks form on the skin, which you can easily scrape off and fortunately do not penetrate the potatoes. The tubers can also remain small and deformed when infested. There is also an infestation of Rhizoctonia problems as early as the beginning of the vegetation of the potato, since damage to the roots can occur. In this case you will find missing spots on the tuber, dark spots on the seedlings and dead shoot tips.

A very well-known symptom is called "dry core": This shows up with sunken round spots on the shell, with the tissue beneath mostly destroyed and sharply demarcated from healthy tissue is. These rotten spots can even fall out and then resemble one wireworm infestation.

In particularly humid summers, white thorns also appear, in which a grayish-white fungus lawn forms at the base of the stem. This is the sexual stage of the fungus.

Rhizoctonia on cereals

At grain occurs among other things Rhizoctonia cerealis and causes so-called eyespots on the grain stalks. A pointed spot with a brown edge and a light inner surface forms at the base of the culm. If you cut open the stalk, you can then find a cotton-like mushroom mycelium. In Germany, the damage caused by this fungus is rather low, the danger is only slightly higher in cool and damp weather.

On grain can also Rhizoctoniasolani occur as a casserole disease. The seedlings are already infested in the ground and there is little emergence.

Rhizoctonia on carrot

Violet root killer or Rhizoctonia crocorum becomes an illness carrots called, which covers the beet from the top with a violet mushroom network, so that it begins to sink in slightly and to rot.

But you can also use the carrot Rhizoctonia carotae appear. Here, a white mycelium forms on the carrots, which resembles a spider's web. Later it turns yellowish-brown and yellow drops form. These Rhizoctonia-Art is a dreaded storage rot pathogen in carrots.

Rhizoctonia on legumes

On legumes such as kidney beans or peas kicks Rhizoctoniasolani also up. This slows down growth, leaves turn yellow and the plants wither. Often the base of the stem also begins to turn black and rotten.

Rhizoctonia on tomatoes

Leads in the case of tomatoes Rhizoctoniasolani to seedling diseases, since the seedlings die before or shortly after emergence. Watery spots can form on the stems, which appear constricted. This causes the tomato plants to tip over.

Rhizoctonia on lettuce

The black rot in various salads is through Rhizoctoniasolani causes and causes the outermost leaves of the lettuce, which are lying on the ground, to become either brown and wet-rotten or dry and paper-thin. This rot then extends to the heart of the head of lettuce. This disease is becoming more and more important in lettuce and occurs especially at high temperatures.

Rhizoctonia on onion

Occurs in bulbous plants Rhizoctoniasolani as a seedling disease and causes damage to the germinating onions. The onions suffer particularly great damage when emergence is slow because they were planted too deep or the weather is cool.

Prevent and avoid Rhizoctonia

Rhizoctonia prefers moist soil conditions. Therefore, you should make sure that no waterlogging forms in your garden. Avoid compaction and try to have a well-aerated healthy soil through thorough tillage. It is also best to bring in organic matter to keep soil life active.

Crop rotation in the garden is also particularly important: If you have ever had problems with a root rot pathogen such as Rhizoctonia you should absolutely avoid planting plants in this place in the next few years that are also from Rhizoctonia can be attacked. Since the outlasting organs of the fungus can survive in the soil for up to three years, there is a risk of reinfection. To protect your plants, you can also use plant-strengthening manure, which increases the resistance of your plants in the garden. These include, for example, nettle or horsetail manure. Horsetail manure is particularly suitable for combating Rhizoctonia, since it shows antifungal activity. You can find out more about these plant manures here.

In addition, only use healthy plants and high-quality seeds, because sickly plants can bring many pathogens into the garden and you may not be able to get rid of them. At the beginning you should also make sure that the seed germinates quickly, because the longer the germination takes, the more time the fungus has to attack the seedlings. Of course, you can also pregerminate the seedlings to give your plants a head start in development.

Control Rhizoctonia

Unfortunately for soil-borne fungi there are such Rhizoctonia not many ways to combat an acute infestation. Rely on plant strengthening and optimal soil conditions to make it not too easy for fungal diseases. In an emergency, you can tackle the fungus with chemical pesticides: for the allotment garden area, for example, there are pesticides that combat Rhizoctoniasolani Show effects. At the moment, work is also being done on a seed treatment with which the seed can be treated before it is sown, thus preventing infestation. In addition, there are already resistance breeds so that the plants independently have a higher tolerance or resistance to fungi such as Rhizoctonia develop.