Fight nematodes: recognize & get rid of - Plantura

Some nematodes harm plantzen, while others are useful against plant pests. We show how harmful nematodes can be combated.

The nematodes, also known as roundworms, are extremely problematic pests, both for the hobby gardener and for the farmer. While in the past it was still allowed to fight the nematodes living in the soil with very environmentally harmful nematicides, combating them with chemical pesticides is now prohibited. Of course, after this ban, the nematodes did not disappear, which is why new, biological ones are now being introduced Methods must be used and tested so that nematode control can continue to be possible is.

harmful nematodes

All relevant plant-damaging nematode species live in the soil and infest the roots of their host plants in different ways. What all species have in common is that they are microscopic and can occur in millions in one cubic meter of earth. Some nematode species remain in the soil, pierce root cells and feed on the exuding plant sap. Some other species, on the other hand, penetrate the plant roots and form typical root galls or cysts. The formation of cysts is one of the important reasons why nematodes are difficult to control. In these cysts, the roundworms are well protected and can survive for about 20 years without food.

In addition to their stubbornness, the different nematode species are also capable of infesting almost any of our delicious garden plants. If carrot, celery, pea, Spinach, cucumber, tomato or potato - the list could be extended indefinitely. In principle, no crop is safe from the eel-like pests. However, as you will see below, there are plants that have developed defense mechanisms against root-damaging nematodes in the course of evolution.

detect nematodes

A nematode infestation is not so easy to recognize. While the typical galls and cysts can be easily located by digging up the roots, symptoms caused by other nematode species are difficult to identify. So that you can quickly see if your garden is infested, we have summarized the most important symptoms that indicate a nematode infestation:

• Root beard: Very many fine and strongly branched roots, which resemble a beard
• Root rot: Resulting from subsequent infections that can enter through the punctured root cells
• An overall short root system, which has many lateral roots
• Growth depression, wilting and loss of yield due to the damaged roots
• In larger vegetable beds, a nest-like occurrence of the symptoms described above is a sure sign of a nematode infestation

Nematodes on potatoes

Especially in potato cultivation, the two potato cyst nematodes do Globodera rostochiensis and Globodera pallida big problem. An infestation is easy to recognize by the small white-yellow, pin-sized cysts on the potato roots. Typical of infested potatoes is reduced growth, small leaves and increased formation of side shoots. Overall, the symptoms lead to severe yield losses. In addition to the potato, the two nematode species also eat other nightshade plants such as aubergine, tomato and nightshade weeds. Although the cysts of the nematodes can survive in the soil for about 20 years, a break in cultivation of 4 years is enough to starve out the majority of the nematodes. In addition to potatoes, no other nightshade plants should be cultivated on the bed during the break in cultivation. In addition, there are other practical ways to combat nematodes in the soil:

• resistant potato varieties Use in case of nematode infestation: Christa, Firstling, Gloria, Ukama or Quarta (maybe in stores soon: Trabant, Valdivia)
• During a break in the cultivation of nightshades, not only volunteer potatoes but also nightshade weeds such as black nightshade or bittersweet nightshade must be removed
• In the case of extreme damage caused by nematodes, so-called fallow land can help - you can find out what a fallow land is in the chapter Fighting nematodes in the soil
• Tagetes do not help against the "potato nematodes"

Nematodes on tomatoes

Unfortunately, tomato roots are also one of the favorite foods of nematodes. In contrast to the potato, however, tomatoes are preferred by gall-forming nematodes such as Meloidogyne hapla and Meloidogyne arenaria infested. Above-ground symptoms are often not properly recognized in tomatoes. However, if the yield from your tomato plants is declining year after year and the tomatoes are grown in the same location, gall nematodes may be to blame. Unfortunately, one of the tomato roots has to be dug up to check. The galls are located directly at the roots and appear like small (2 to 4 mm) ulcers. Against the nematode species commonly found in the field M hapla Unfortunately, only consistent crop rotation helps. For control, the 2- to 3-year cultivation of maize is recommended. Corn does not serve as food for the nematodes, so growing it consistently starves them. Many other vegetables like carrots, leeks and celery However, they are host plants and must therefore not be cultivated on the same area.

On the other hand, there are varieties that are resistant to heat-loving gall nematodes, which prefer to attack tomatoes in greenhouses and under foil, for example:

• Caprese, Corianne, Ducati, Dolcevita, Matias, Picolino and Zebrino.

And another piece of good news for lovers of others tomato varieties: With the rootstock Vigomax you can in principle make all tomato varieties resistant to the heat-loving gall nematode. More tips on the topic Pests on Tomatoes you'll find here.

fight nematodes

When combating nematodes, the focus is not on completely eliminating all pests. This goal is utopian and cannot be achieved with practically any countermeasures. Rather, it is about reducing the nematode population to such an extent that the small number of roundworms no longer causes any visible damage. In the next few years, it is very likely that new biological control measures will come onto the market, which are currently being researched. The focus of science is primarily on fungi, which the nematodes with microscopically small capture lasso-like threads and then render them harmless, or the eggs of small nematodes infested.

Control nematodes in the soil

As a rule, nematodes can be controlled very effectively by starving them out - but how does that work? In principle, it is only necessary to ensure that no host plants are available for the harmful nematodes to feed on a bed infested with nematodes. However, that is easier said than done. Since it is not possible to determine the individual nematode species in practice, it is usually difficult to choose the right crop rotation. Because the different species can infest a large number of plants and also use a wide range of plant species as hosts. So if you are not sure which nematode species affects your plants, then we recommend black fallow. With this biological control measure, the bed is kept free of plants over a longer period of time. This measure is particularly effective if you observe the following points:

• For nematode control, the bed should lie fallow for at least 4 - 5 months
• In summer, nematodes are particularly dependent on food, so starvation tactics work particularly well during this period
• Weeds should also not grow in the field during this period, so rake them out regularly
• Disadvantage: the open ground is unprotected during this period and threatened by wind erosion

Thermal control measures are also available to horticulture. Like all soil dwellers, nematodes are very sensitive to high temperatures. Using special steam devices, the soil can be heated to such an extent that even deep-seated nematodes are effectively combated. However, this method is very expensive and unfortunately not practical for us hobby gardeners.

Fight nematodes chemically?

Our garden soil is inhabited by an almost innumerable number of microorganisms. In addition to its sheer mass, the variety of species is almost inexhaustible. All of these soil creatures take on essential functions in the nutrient cycle. Plants decompose and the nutrients released as a result can be reabsorbed by other plants. Microorganisms such as earthworms literally till the entire soil and thus ensure good ventilation of the plant roots. If pesticides against nematodes in the soil were used on a large scale at this point, everyone can imagine what the consequences would be. The long-term damage to other organisms would be difficult to calculate, as would the risk of groundwater contamination.

One of the ways in which nematodes were fought was with toxic gases that were injected into the soil. However, these control measures also had significant side effects on other organisms and sometimes even on humans. For this reason, the use of chemical pesticides, so-called nematicides, is generally prohibited throughout Germany.

Marigolds against nematodes

As mentioned at the beginning, there are plants that form antibodies against nematodes and can thus fight them. One plant that has perfected this mechanism is tagetes. The plants form so-called terthiophenes, which have a toxic effect on nematodes. If a nematode gets to a marigold plant and wants to absorb the plant sap at the roots, it will be killed by the toxins it contains. And this is exactly where the limitation in the effectiveness of marigolds lies. Only species of nematodes that regard marigold plants as host plants and puncture their root cells are controlled. For this reason, gall and cyst nematodes are almost never combated by marigolds. Free-living nematodes from the Pratylenchus genus can be recorded all the better. These free-living nematodes like to infest vegetable crops such as carrots, celery, beans, salad, onions, peas and leeks and can become a major nuisance in the vegetable patch. You can best combat large accumulations of nematodes with an area-wide intercropping of marigolds. Proceed as follows:

1. Use a 1:1 mix of Tagetes patula and Tagetes erecta; these two strains are very effective in nematode control
2. Keep in mind that marigolds are not frost hardy and should be left on the bed for at least three months to have a sufficient effect.
3. In addition to caring for the marigold plants, all weeds must be removed regularly if possible

This biological control method can reduce a nematode population by up to 90% in the long term so it is an effective biological measure against free-living nematodes such as Pratylenchus.

Nematodes can do much more damage than just your plants: some of the roundworm species also fight other pests. Here you will find all information about the use of Nematodes as beneficial insects in the garden.