Phytophthora infestans: Recognize & combat

Phytophthorainfestant is one of the most feared fungal pathogens. Here's how to identify and fight the infestation.

Suddenly your plants begin to wither, although nothing unusual can be seen at first glance? Strange spots form on the leaves and only rotten tubers are found at harvest? The cause of this could be a representative from the genus Phytophthora be.

Phytophthora: characteristics and origin

The Egg Mushroom Phytophthora infestans originally comes from Central America and in the 19th Century already caused epidemics in Europe. A well-known example of the devastation caused by this fungus is the Great Famine in Ireland between 1845 and 1852. At that time the potato was one of the staple foods and in Ireland at that time there were only two varieties of potatoes that were very susceptible to this egg fungus. Coupled with Ireland's humid climate

Phytophthora infestans optimal conditions and the resulting crop failures cost the lives of around one million people. This probably proves what kind of damage this egg mushroom can cause - especially in damp weather. Incidentally, egg fungi are not “real” fungi, but a separate group of organisms that are more closely related to algae than to fungi, for example.

Temperatures of 15 to 23 °C and high humidity are ideal for the egg fungus to start growing. We find these conditions outdoors mostly in June. If the egg fungus, which has overwintered on crop residues, has moisture for ten hours at a time, the permanent spores begin to grow and germinate. The spores can be spread by the wind or find their way into your garden through the patter of rain on your plants. When the spores hit the plant, they need moisture to germinate and penetrate the plant. There they form spores and infect the entire plant from there. Potato tubers become infected with the rot either this way or through spores that have already been in the soil.

Phytophthora is extremely adaptable and can even survive longer periods of drought without any problems. It can also quickly adapt to control methods, which means that resistance to certain pesticides that are used over and over again develops in no time at all.

Phytophthora: host-specific species

the Phytophthora-Fungi are a very large group of fungi. Most species specialize in certain plants or plant families. The egg mushrooms not only attack our vegetable crops in the garden, but also trees and shrubs.

A few examples:

• Phytophthora infestans: Late blight on potatoes; Late blight and late blight on tomatoes
• Phytophthora cactorum: Leatherberry disease on strawberries; twig dieback on rhododendron; Collar rot on apple
• Phytophthora cinnamomi: heather death
• Phytophthora fragariae: Red root rot on strawberries
• Phytophthora sojae: Crown and shoot rot on asparagus
• Phytophthora ramorum: Dying shoots on rhododendrons;. oak dieback
• Phytophthora syringae: lilac wilt
• Phytophthora rubi: dying roots of raspberries

Phytophthora infestans: The late blight

This type of egg fungus has a narrow range of host plants: it only affects nightshade plants (Solanaceae). The infestation usually causes yield losses of 8 to 10%. In rainy years, the fungus can spread like an epidemic and destroy up to 70% of your harvest.

Late blight on potatoes

at potatoes (Solanum tuberosum) infected with late blight, petioles and stalks turning brown can be seen. In addition, yellow-green to later brown spots can appear on the leaves. These spots appear water-soaked and start at the edges of the leaves. When the humidity is high, a white fungal coating also forms on the underside of the potato leaves. Eventually the leaves will dry up and rot. The symptoms of the tubers are superficially sunken, gray spots and brown discoloration inside the tubers, which cannot be clearly differentiated from the healthy tissue. The tubers also turn brown and rot at the end.

Late blight and late blight on tomatoes

If your tomatoes (Solanum lycopersicum) with the Late blight and late blight are infested, it can easily be that the infection started in an infested potato patch. The egg fungus usually grows first on the potatoes and the spores then often infect your tomatoes as well. The first signs are wilting leaves, which turn grey-green and die off. You can also see a white fungal coating on the leaves. The stalks can show dark spots, but often the egg fungus can only be recognized when the tomatoes are ripe. The tomato fruits become dull and hard spots form that begin to wrinkle. The tomatoes then rot and are inedible.

Phytophthora detect

If you notice the above symptoms on your plants, you can assume that they are Phytophthora is in your garden. However, there are also possibilities for confusion:

• Rotting your potato tubers can also cause early blight. However, the rotten spots on the tubers are clearly separated from the healthy tissue and show rings. at Phytophthora the rotten tissue is not clearly demarcated from the healthy tissue. Spray spots appear on the leaves and these can fall out.
• You can with tomatoes Phytophthora confused with blossom end rot. This rot is caused by a lack of calcium and always starts at the point where the calyx has separated from the ovary. There is only a large, brownish, sunken rotten spot on the fruit.

Phytophthora prevent successfully

The most important thing in the prevention of Phytophthora is the use of healthy seedlings and less susceptible varieties. Unfortunately, there are not many varieties of it on the market at the moment. Waxy varieties of potatoes are less at risk.

As already mentioned, moisture is very important for the egg mushroom. This means that plants that form dense stands, such as bush tomatoes, are more at risk. Denser stocks dry more poorly - this promotes fungal infestation.

It is also important to follow crop rotation in the garden. Should ever Phytophthora appeared in your bed, it is advisable not to plant nightshades (Solanaceae) to grow more.

Since the spores are spread by rain and spray water, care must be taken to water the plants carefully. If you work with irrigation (for example in your greenhouse) you should rely on drip irrigation instead of sprinkling. Since moisture and splashing water are the biggest problem in the treatment of egg fungus, it is recommended to use a Put up a small canopy for your tomatoes or place the plants in a rain-protected, sunny spot to set up. A terrace or the wall of a building is suitable for this, in order to raise the tomatoes in a protected manner.

More tips to prevent Phytophthora:

• Do not overdo with the fertilizer:
  Do not use too much nitrogen fertilizer, over-fertilizing can encourage the growth of the egg fungus. A potassium-rich slow-release fertilizer like ours Plantura organic tomato fertilizer is a very good choice for prevention.
• Avoid waterlogging:
  Drain your garden or work in some gravel or sand to loosen the soil. This promotes the drainage of water and improves the water and air balance in your garden.
• Be careful when harvesting:
  Be careful not to damage anything when harvesting and also check your stored tubers for infestation.
• Dispose of crop waste:
  Since the egg fungus overwinters in infected parts of the plant, such crop residues and parts of the plant should be removed as a precaution to prevent an infestation next year.

Phytophthora combat efficiently

Has it now happened despite all precautions that? Phytophthora occurs in your area, it is important to remove the infected, diseased plants. Don't dispose of infected plants in your compost - these diseased plants belong in the household waste, where they can no longer infect other plants. Since this egg fungus overwinters on the crop residue, these parts should not end up on the compost or be left in the garden.

Also thoroughly clean and disinfect any equipment that has come into contact with the diseased plants. If the infestation is very severe, you can also replace the contaminated soil with fresh one. Be careful not to spread the infection further.

Another control option is fungicides. However, most of these crop protection products have a preventive effect and should be used in damp weather.

When using pesticides, careful handling is the most important thing. Always read the instructions for use before use and follow the instructions.

Another fungus that troubles many plants is the egg fungus pythium. We have information for you on how to recognize and combat Pythium.