Rhizoctonia: Avoid & fight beet rot

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

Rhizoctonia not only affects our beets, but also damages many other plants. It is a dreaded emergence disease, which is also often called the root killer.

Rhizoctonia

The mushroom Rhizoctonia is on everyone's lips when it comes to root and emergent diseases. We explain below what the fungus is and how you can fight and avoid it.

Rhizoctonia: characteristics and distribution

The correct name of this mushroom stand is

Thanatephorus cucumeris - only becomes its asexual or anamorphic form Rhizoctonia called. Among other things, the fungus can cause late beet rot, white hatred or potato pox. It is widespread worldwide and is native to the world. There are a couple of subsets of Rhizoctoniasolanithat only occur in certain parts of the world, such as the Philippines, Japan or the USA.

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

The outbreak of the disease is triggered by external factors. The fungus is present in all soils, but warm temperatures and waterlogging promote the infestation. Rhizoctonia also very often causes seedling diseases and casserole damage. Conditions conducive to 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 is not just one type of Rhizoctoniabut many different ones, each of which differs in its preferred host plant and its harmful effects. Here is a brief overview of the various Rhizoctonia-Species:

• Rhizoctonia solani: Often occurs on beets, legumes, cereals, tomatoes, salads, and potatoes; can survive as mycelium or form so-called sclerotia, which serve to persist the fungus in the soil; In contrast to other mushrooms, it does not form spores
• Rhizoctonia cerealis: Also called an acute eye spot and occurs on grain
• Rhizoctonia crocorum: Also called the purple root killer and occurs on carrots
• Rhizoctonia carotae: Is a storage rot agent in carrots

Recognizing 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 beets

The late beet rot often occurs Rhizoctonia solani on beets like Beetroot, Swiss chard or sugar beets and causes the beet plants to wither from the outside in. The leaves then turn yellow and lie in a wreath around the beet on the ground. On the beets, dark brown, dry rot spots can also be seen that extend far into the beet. Even if the beet has already died, it continues to shrink.

Rhizoctonia of potatoes

Also on potatoes some symptoms can develop if they are affected by Rhizoctonia solani are infested. For example, dark brown to black potato poxes form on the skin, which you can easily scrape off and which, luckily, do not penetrate the potatoes. The tubers can also remain small and deformed in the event of an infestation. There is also an infestation of Rhizoctonia Problems at the beginning of the vegetation of the potato, as it can lead to overrun damage. 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, rounded areas on the shell, whereby the tissue underneath is mostly destroyed and sharply demarcated from healthy tissue is. These rotten spots can even fall out and resemble one Wireworm infestation.

In particularly humid summers, whiteness is also evident, in which a grayish white fungal lawn forms at the base of the stem. This is then the sexual stage of the fungus.

Rhizoctonia on cereals

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

You can also use grain Rhizoctonia solani appear as a disease of emergence. The seedlings are already attacked in the ground and there is little emergence.

Rhizoctonia on carrot

Purple root killer or Rhizoctonia crocorum becomes a disease Carrots called, which covers the beet starting from the tip with a purple fungal network, so that it begins to sink in and rot.

But you can also use the carrot Rhizoctonia carotae appear. Here, a white network of mushrooms 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 Haricot beans or peas occurs Rhizoctonia solani also on. Growth is delayed, the leaves turn yellow and the plants wilt. Often the base of the stem also begins to turn black and rotten.

Rhizoctonia on tomatoes

When it comes to tomatoes, it leads Rhizoctonia solani to seedling diseases, since the seedlings die before or shortly after emergence. Watery spots that appear constricted can form on the stems. This also causes the tomato plants to tip over.

Rhizoctonia on lettuce

The black rot in various salads is through Rhizoctonia solani causes and causes that the outermost leaves of the lettuce, which lie on the ground, either turn brown and wet rotten or dry and wafer-thin. This rot then extends into the heart of the head of lettuce. This disease is becoming more and more important in salads and occurs particularly at high temperatures.

Rhizoctonia on onion

Occurs in onion plants Rhizoctonia solani emerges as a seedling disease and causes damage to the germinating ones Onions. The onions suffer particularly great damage if they emerge slowly because they have been set too deeply or the weather is cool.

Prevent and Avoid Rhizoctonia

Rhizoctonia prefers moist soil conditions. You should therefore make absolutely sure that no waterlogging forms in your garden. Avoid compaction and try to have well-ventilated healthy soil through thorough tillage. It is also best to bring in organic matter to keep the soil life active.

The crop rotation in the garden is particularly important: If you have ever had problems with a root rot pathogen like Rhizoctonia, you should absolutely avoid in the next few years planting plants that are also from Rhizoctonia can be infested. Since the perennial organs of the fungus can survive in the soil for up to three years, there is a risk of renewed infection. To protect your plants, you can also use plant-strengthening liquid manure, which increases the resistance of your plants in the garden. These include, for example, nettle or field horsetail manure. Field horsetail manure is particularly suitable for combating Rhizoctonia, as it has an effect against fungi. You can find out more about this plant manure here.

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

Fight Rhizoctonia

Unfortunately for soil-borne mushrooms like Rhizoctonia not many ways to combat an acute infestation. Rely on plant strengthening and optimal soil conditions to prevent fungal diseases from becoming too easy. In an emergency, you can attack the fungus with chemical pesticides: For allotment gardens, for example, there are pesticides that counteract Rhizoctonia solani Show effects. At the moment we are also working on a seed treatment with which the seed can be treated before it is sown and thus an infestation can be prevented. In addition, there are already resistance breeds so that the plants independently have a higher tolerance or resistance to fungi such as Rhizoctonia to develop.