Pythium: Recognize & combat the root fungus

Pythium is an egg fungus that severely affects plant roots and can even kill the plant. We show what you can do against Pythium.

The names root rot or blackleg denote the same as Pythium. A soil-borne, fungal-like pathogen that causes rot on our garden favorites. Everything you should know about this "fungus" and how you can fight and get rid of it can be found here.

Pythium: way of life and life cycle

Pythium belongs to the order Oomycetes and family Phytiaceae and has a very wide host range. Pythium is a so-called egg fungus or pseudofungus. Egg fungi are actually more closely related to algae than to real fungi, and they also include plant diseases such as

Phytophthora infestans or the wrong one mildew. The egg fungus prefers moist soil with a low oxygen content, so plants on soil prone to waterlogging are particularly threatened by Pythium. Depending on the stage of development of the egg fungus, the germination of the spores and the subsequent infection of a host plant is also favored by cooler temperatures (10 to 17 °C) and periods of low light will. The egg fungus is one of the typical causative agents of casserole diseases. Damping diseases often cause seedling toppling or seedling death before they even break the surface. The following conditions favor the occurrence of Pythium:

• Waterlogged, moist soil
• Low oxygen level
• soil compaction
• High pH
• lack of light
• Daytime temperatures above 30°C and nighttime temperatures above 20°C

The development cycle of Pythium

The egg fungus develops in two phases: In the first, sexual reproduction takes place and oospores are formed. These thick-walled oospores are designed to survive unfavorable conditions. These permanent spores survive in the soil, in plant tissue or in water and can also stick to garden tools. As developmental conditions improve, the second phase of development, that of growth and dispersal, begins. The permanent spores of the egg fungus then form so-called swarming spores. These spores seek out the host plants and penetrate the roots through injuries or soft stretching zones. There is a strong increase there. If the roots dry out, the egg fungus dies and outlasting spores form. These can then germinate again under favorable conditions. This egg fungus can only occur in the soil or in underground plant parts. Favorable conditions for swarming spores are at temperatures of 10 - 17 °C and for persistent spores 25 °C in combination with humidity.

Pythium: damage patterns and symptoms on plants

Like all root diseases, Pythium causes wilt, yellowing, stunted growth and brown rotten roots. The roots rot from the root tip and the bark peels off. You can even strip the bark off the roots so that only the so-called "rat tails" remain, i.e. the inner part of the root.

However, a special feature of Pythium ultimum is that the infestation causes constriction in the area between the root and the stem. This area usually turns brown, the base of cuttings turns black and they tip over. Hence the name blackleg. Of course, it can also lead to a complete failure. The egg fungus can also attack the seedlings and prevent them from opening at all.

Onions become watery and rotten when infested. In the worst case, your plant will even die. Unfortunately, this happens because the rotten roots can no longer absorb water and nutrients and the stability also decreases.

Beware of confusion: There is also a strain of the soil fungus that does not cause any damage, i.e. is not a plant pathogen. On the contrary, the M1 strain of Pythium oligandrum is an extremely helpful and legal plant strengthener. The spores of this fungal strain are the active ingredient in the plant strengthener Polyversum and help against various fungal diseases. Pythium oligandrum suppresses other harmful fungi by feeding on them - it is therefore also called a hyperparasite. The fungus also colonizes the plants and increases their defenses against fungal infections. This remedy is used especially against Fusarium and root diseases.

Pythium on the pea

At the pea (Pisum sativum) especially the species P. ultimate., P. debaryanum, P. aphanidermatum and P. arrhenomanes before. The seedlings are damaged before emergence and then fall over. Older plants can also suffer damage to the roots. P ultimum can also cause shoot tip burns in older plants. The tips look watery at first, then begin to dry up and die off. However, the whole pea plant rarely dies. High humidity and temperatures between 24 and 28 °C have a positive effect.

Pythium on cucumber, melon, pumpkin, zucchini and tomato

Also on fruit vegetables like cucumber, melon, pumpkin, zucchini and tomato can cause Pythium seedling damage. The species P. aphanidermatum, P. debaryanum, P. myriotylum, P. ultimate and P uncinulatum responsible.

Pythium can also cause stem rot on these types of vegetables. The damage occurs after planting out. There is a glassy, ​​grey-green discoloration of the base of the stem, which later turns brown. The stalk constricts and begins to rot, right between the ground and the cotyledons. As a result, hardly any roots grow and the plants die within 2 weeks.

For tomatoes (Solanum lycopersicum) creates a watery zone on the stem near the ground after planting. This point then also constricts and causes the tomatoes to tip over. A lot of moisture and little light are particularly beneficial. Stem bottom rot is caused by the Pythium species P. aphanidermatum, P. irregulare, P. sylvaticum and P. ultimately caused.

Pythium on parsley

If the parsley (Petroselinum crispum) falls over or withers, Pythium may be the reason. Especially P mastophorum is particularly aggressive on parsley, but P. ultimate, P irregulare, P. paroecandrum and P. sylvaticum can cause damage. Constrictions also appear on the stems of the seedlings of parsley, and older plants that have already reached a height of 10 cm are also affected. Grey, brown or rust-brown spots appear on the roots. If the infestation is severe, the lateral roots are missing or only brown stumps remain. The parsley will begin to turn yellow and eventually die.

Pythium on the carrot

Root and tuber vegetables, like that carrot (Daucus carota) or radish (Raphanus sativus) are particularly threatened by Pythium root rot on waterlogged soil. The first signs appear at a carrot size of 10 to 15 cm. The carrots look limp during the day, but recover at night. Growth begins to falter and the leaves change color. More lateral roots are formed and the root tissue is soft and discolored rusty red.

Pythium water spot disease causes translucent and sunken infestations that can be up to 5mm deep on the beet. If you remove the skin of infected carrots, you can see black wart-like formations. This disease (cavity spot) is an important issue in carrot cultivation and is caused by P. violae and P sulcatum caused.

pythium on celery

The seedling disease and root rot is at celery (Apium) by P mastophorum and some other species. During cultivation, the seedlings wilt like nests and turn yellowish. In addition, the cotyledons begin to fall off and the seedlings are squashed. Because their roots shrink, the seedlings are also easy to pull out of the ground. The roots turn rusty brown, even in older plants, causing them to rot and ultimately die.

pythium on the salad

Also at salad (Lactuca sativa) there are seedling diseases caused by Pythium infestation (P irregulare, P. sylvaticum). The lettuce wilt in lettuce and endives (Cichorium endivia) is caused by Pythium in spring and autumn. In hot and dry weather, the damage of P. tracheiphilium. The lettuce has a reduced growth, if you cut through the head of lettuce, you can see brown vessels. Necrosis is visible on the petioles, and yellowing and dying of the leaves can even occur. The lettuce can be pulled out of the ground without tearing off the roots. These appear strongly necrotic.

Pythium: What to do?

There are a few ways to get rid of this dreaded fungus. For a long time, "hygiene" in the garden was the most important control strategy against damp-off diseases. Everything was sanitized and still root diseases like Pythium found their way to the plants. In the following section we will tell you which methods work better.

“Pythium: Combat Biologically”

Studies show that there are bacteria and fungi that are good antagonists to soil-borne pathogens. Therefore, these organisms can be used for biological control of Pythium. For example, you can apply the hyperparasitic fungus Trichoderma harzianum. But also Gliaocladium sp. manages to displace the harmful fungus.

The biological fungicide Prestop can be used against various Pythium species on young plants, vegetables and ornamental plants. It is applied by pouring or spraying. This biological fungicide is based on the hyperparasitic soil fungus Gliocladium catenulatum.

The agent has three mechanisms of action: It parasitizes the harmful fungus and kills it. In addition, the drug produces enzymes that suppress the growth of the fungus. The last mechanism of action works through competition. Due to its strong growth, the fungicide displaces the harmful fungus because it deprives it of its habitat. Preparations with Trichoderma also work using this mechanism of action.

“Pythium: fight chemically”

For larger-scale cultivation, the seed is often treated with special agents to prevent fungal infection. Dressing means that the seed is coated with a crop protection product before it is sown - this protects it. However, such agents are not approved for home use.

Successfully avoiding Pythium

The key to avoidance and prevention is controlling your location. Humidity is particularly favorable for this egg fungus, so you should try to keep your garden dry and especially avoid flooding. If you have particularly heavy and wet soil, try incorporating sand or gravel to help the water drain better.

You can use compost in the garden as a preventive measure. Beneficial fungi are often found in this soil, fighting harmful organisms through competition and parasitic behavior.

As already mentioned, lack of light encourages the growth of Pythium. Therefore, your sowings in particular should always get enough light. Do not grow your darlings in a dark corner, but on a sunny windowsill in clean planters. When growing plants, you can also pay attention to a few things to avoid the risk of a To reduce Pythium infection: the temperature should be around 19 °C, the healthy substrate must be as dry as to be possible. It is best to plant your little protégés in the evening. The water should not be too cold either. If you are using drip irrigation, make sure the watering is not aimed directly at the stem.

You can also use plant strengtheners from field horsetail (Equisetum arvense) use. The field horsetail broth has a preventive effect against soil fungi and also serves as a tonic for our plants. Field horsetail manure can be used, especially in the case of seedling diseases, and the manure can be poured over the growing soil beforehand. To protect the seedlings from soil fungi when they are released, you can treat the seedlings to a short root bath in horsetail manure. As a preventive and direct defense against fungi, you can also water the plants with this liquid manure in the morning.

Here you can find out more about the field horsetail and its possible uses.

Prevention in a nutshell:

• Keep your garden beds dry and airy
• Use compost
• When growing plants:
  • Enough light
  • Clean growing vessels
  • cultivation temperature approx. 19ºC
  • Do not water too cold
  • Plant out in the evening
• Field horsetail manure for plant strengthening (and fungus control)

Pythium or Phytophthora: The difference

Pythium sp. and Phytophthora sp. both belong to the class Oomycetes and therein to the family Pythiaceae, but to different genera. Nevertheless, these two fungi often occur as a mixed infestation. However, Pythium is less host specific than Phytophthora. Phytophthora is also more aggressive than Pythium because Phytophthora can also attack and kill mature plants. Both fungi prefer waterlogged soils with low oxygen levels and cause seed toppling and root rot.

The two pathogens cannot be told apart from the externally recognizable symptoms of rot alone. The exact distinction can only be made by examining the spores of the fungi - especially since these pathogens have many different representatives, on different cultures, for example Pythium ultimum or Phytophthora infefstans.

How himself Phytophthora developed and what you can do best against this fungus, you can find out here.