- Rhizoctonia
- Rhizoctonia: characteristics and distribution
- Rhizoctonia species and host plants
- Recognize Rhizoctonia: damage and symptoms
- Preventing and avoiding Rhizoctonia
- Control Rhizoctonia
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The famous beet blight is just one species of Rhizoctonia. We show you how to recognize the fungus Rhizoctonia and what to do about it.
Rhizoctonia not only affects our beets, but also causes damage to many other plants. It is a dreaded casserole disease, which is also often called root killer.
Rhizoctonia
The fungus 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 mushroom is Thanatephorus cucumeris - only its asexual or anamorphic form is called Rhizoctonia. 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 Rhizoctonia solani that are only found 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 entered, 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
- Poor soil structure
- oxygen deficiency
- Low pH
Rhizoctonia species and host plants
There is not just one species of Rhizoctonia, but many different ones, each of which differs in their preferred host plant and their harmful effects. Here you will find a brief overview of the various Rhizoctonia species:
- Rhizoctonia solani: 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; unlike other mushrooms, does not form spores
- Rhizoctonia cerealis: Also known as the pointed eyespot and occurs on cereals
- Rhizoctonia crocorum: Also called the purple root killer and occurs on carrots
- Rhizoctonia carotae: Causes storage rot in carrots
Recognize Rhizoctonia: damage and symptoms
Rhizoctonia can cause various symptoms, which we briefly describe below. Symptoms differ depending on which crop the fungus occurs on.
Rhizoctonia on turnips
Beet rot caused by Rhizoctonia solani often occurs on beets such as beetroot, chard or sugar beets 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 when the beet has died, it keeps shrinking.
Rhizoctonia on potatoes
Potatoes can also develop some symptoms if they are infested with Rhizoctonia solani. 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 are also problems with an infestation of Rhizoctonia right from the start of the potato's vegetation, 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 as sunken round spots on the shell, with the tissue underneath mostly being destroyed and sharp from thehe althy tissue is demarcated. These rotten spots can even fall out and then resemble a wireworm infestation.
In particularly humid summers, white thorns also appear, in which a greyish-white fungus lawn forms at the base of the stem. This is the sexual stage of the fungus.
Rhizoctonia on cereals
Rhizoctonia cerealis
occurs on cereals and causes so-called eyespots on the cereal 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 cereals, Rhizoctonia solani can also occur as a dampening disease. The seedlings are already infested in the ground and there is little emergence.
Rhizoctonia on carrot
Purple root killer or Rhizoctonia crocorum is a disease of carrots that covers the beet starting from the top with a purple fungal network, causing it to sink in slightly and rot.
But Rhizoctonia carotae can also occur on the carrot. Here, a white mycelium forms on the carrots, which resembles a spider's web. Later it turns yellowish-brown and yellow drops form. This Rhizoctonia species is a dreaded carrot storage rot pathogen.
Rhizoctonia on legumes
Rhizoctonia solani also occurs on legumes such as garden beans or peas. 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
In tomatoes, Rhizoctonia solani leads to seedling diseases, as the seedlings die before or shortly after emergence. Watery spots can form on the stems, which appear constricted. This will cause the tomato plants to fall over.
Rhizoctonia on lettuce
Black rot in various lettuce is caused by Rhizoctonia solani and causes the outermost leaves of the lettuce that are lying on the ground to either turn brown andbecome 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 is particularly evident at high temperatures.
Rhizoctonia on onion
In bulbous plants, Rhizoctonia solani occurs as a seedling disease and causes damage to the germinating bulbs. Onions suffer particularly great damage if emergence is slow because they were planted too deep or the weather is cool.
Preventing and avoiding 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 he althy soil through thorough tillage. It is also best to add organic matter to keep soil life active.
Fruit rotation in the garden is also particularly important: if you have ever had problems with a root rot pathogen such as Rhizoctonia, you should definitely avoid getting rid of this in the years to come Place plants that can also be attacked by Rhizoctonia. 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, as it is effective against fungi. Find out more about these plant manures here.
In addition, only use he althy 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 there aren't many options for combating an acute infestation with soil-borne fungi such as Rhizoctonia. Rely on plant strengthening and optimal soil conditions to make it not too easy for fungal diseases. In an emergency, you can take the fungus with youchemical pesticides: For example, there are pesticides for allotment gardens that are effective against Rhizoctonia solani. 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 develop a higher tolerance or resistance to fungi such as Rhizoctonia .