These nematodes (eelworms, roundworms, trichinae) belong to the most species- and individual-rich animal group in the world, which comprises up to 20,000 different species. Most of them are very small, ranging from 0.1 to about one millimetre (the largest species, at over 8 m, lives in the sperm whale placenta). In contrast to more highly developed arthropods (such as the earthworm), they do not have any vessels. Usually there are males and egg-laying females, but occasionally there is also a sexless virgin procreation (pathenogesis). Until sexual maturity, four larval skins are passed through. The food is taken in through a hollow mouth spike, which moves rhythmically when sucking. They live with numerous species in the soil and also feed on bacteria or fungi, which is a positive element in the ecological system of a vineyard soil.
It was not until the 1930s that they were recognised as a pest of the vine, until then phylloxera was wrongly suspected. In the vineyard there are two groups in particular which are very dangerous for the vine, directly through feeding damage and indirectly as virus carriers. As directly damaging parasites, the species Meloidogyne, Heterodera and Pratylenchus cause bile at the root tips of the vine as a defensive reaction of the vine, which they then consume. Although this does not have as serious an effect as with phylloxera, it does lead to water stress and an insufficient supply of nutrients. These root bile nodules are found mainly in sandy soil. The species Longidorus maximus and Rotylenchus borealis prick the vine roots directly with their mouth prick without bile formation, suck on them and destroy them. The shoots remain behind in development, in extreme cases the vine dies. However, the frequency of the damage is rather low.
The far more devastating effect occurs indirectly, i.e. through the transmission of dangerous viruses. The two species Xiphinema index (only found on the vine) and Xiphinema vuittenezi transmit the Grapevine fanleaf virus (GFV), the species Xiphinema diversicaudatum the Arabis mosaic virus (ArMV), both of which cause brushwood disease. The use of nematode-resistant grapevine rootstocks is considered a preventive defence measure. These include the American species Vitis acerifolia, Vitis champinii, Vitis cinerea and Vitis mustangensis. A formerly common control with nematicides such as DBCP (dibromochloropropane) is no longer permitted in viticulture.
However, nematodes can also be used as beneficial organisms in the context of biological plant protection, whereby there are special preparations for certain plants or pests such as largemouth weevils and owl caterpillars. One sachet can contain up to 2.5 million nematodes. The preparation is dissolved in water and sprayed. The living nematodes spread in this way actively search the soil for the larvae or caterpillars, infest them and cause them to die within a very short time.