Pythium: Detect the Root Fungus Fight &

Pythium is an egg fungus that can damage plant roots and 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. You can find out everything you need to know about this "fungus" and how to fight and get rid of it 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 downy 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 can also be favored by cooler temperatures (10 to 17 °C) and periods of poor light. The egg fungus is one of the typical causative agents of casserole diseases. Damping diseases often cause seedling tipping over or seedling death before they even break the surface. The following conditions favor the occurrence of Pythium:

• Waterlogged, moist soils
• Low Oxygen
• 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. If theDevelopment conditions improve, the second phase of development begins, that of growth and dissemination. 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 at 25 °C in combination with moisture.

Pythium: Damage 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" are left, i.e. the inner part of the root.

But 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 sprout 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 their stability decreases.

Warning risk 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

On the pea (Pisumsativum) the species P. ultimum., P. debaryanum, P. aphanidermatum and P. arrhenomanes occur in particular. 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 beneficial effect.

Pythium on cucumber, melon, pumpkin, zucchini and tomato

Pythium can also cause seedling damage on fruiting vegetables such as cucumber, melon, pumpkin, zucchini and tomato. The species P. aphanidermatum, P. debaryanum, P. myriotylum, P. ultimum and P. uncinulatum are particularly responsible for this.

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.

Tomatoes (Solanum lycopersicum) develop a watery zone on the stalk 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. ultimum.

Pythium on Parsley

If the parsley (Petroselinum crispum) falls over or wilts, Pythium may be the cause. P. mastophorum in particular is particularly aggressive on parsley, but P. ultimum, P. irregulare, P. paroecandrum and P. sylvaticum can also 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, such as the carrot (Daucuscarota) or radishes (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 f alter and the leaves change color. Lateral roots are increasingly formed and the root tissue is soft and rusty red in colour.

Pythium water spot causes translucent and sunken infestations that can reach 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.

Pythium on Celery

Seedling disease and root rot is caused by P. mastophorum and some other species in celery (Apium). 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 eventually die.

Pythium on lettuce

Also in lettuce (Lactuca sativa) there are seedling diseases caused by Pythium infestation (P. irregulare, P. sylvaticum). Lettuce wilt in lettuce and endive (Cichorium endivia) is also caused by Pythium in spring and autumn. P. tracheiphilium damage is evident in hot and dry weather. 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 heavily 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: fight biologically”

Research shows that there are bacteria and fungi that are goodare 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 permitted for domestic use.

Successfully avoid 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 drain water.

You can use compost soil in the garden as a preventive measure… This soil often contains useful fungi that fight 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 reduce the risk of a Pythium infection: The temperature should be around 19 °C, the he althy substrate must be as dry as possible. It is best to plant your little protégés in the evening. The water should not be too cold either. If you use drip irrigation, make sure that theIrrigation is not aimed directly at the stem.

You can also use horsetail plant strengtheners (Equisetum arvense). 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 fungus when they are released, you can treat the seedlings to a short root bath in horsetail manure. You can also water the plants with this manure in the morning as a preventive and direct defense against fungi.

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

Prevention in a nutshell:

• Keep your garden beds dry and airy
• Use compost
• When growing plants:
  • Enough light
  • Clean cultivation vessels
  • Cultivation temperature approx. 19 °C
  • Do not water too cold
  • Plant out in the evening
• 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 stagnant, low-oxygen soils and cause seed toppling and root rot.

You cannot tell the two pathogens apart from the externally visible 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, for example Pythium ultimum or Phytophthora infefstans on a wide variety of cultures.

You can find out here how Phytophthora develops and what you can do best against this fungus.