These nematodes (eelworms, roundworms, trichinae) are among the most species- and individual-rich animal group in the world, with 20,000 different species. Most are very small, ranging from 0.1 to around one millimetre (the largest species, at over 8 m, lives in the sperm whale placenta). Unlike more highly developed arthropods (such as the earthworm), they have no vessels. Usually there are males and egg-laying females, but occasionally there is also a sexless virgin-breeding (pathenogesis). Four larval moults are undergone until sexual maturity. Feeding takes place through a hollow mouth spine that moves rhythmically while 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.
As a pest in the vineyard
In the 1930s, they were recognised as a pest of the grapevine; until then, phylloxera had been mistakenly assumed. In the vineyard, two groups in particular occur, 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 galls on the root tips as a defensive reaction of the vine, which they then consume. Although this does not have as serious an effect as phylloxera, it does lead to water stress and insufficient nutrient supply. These root galls occur mainly in sandy soil. The species Longidorus maximus and Rotylenchus borealis sting the vine roots directly with their mouth spines without forming galls, suck on them and destroy them. The shoots are retarded in their development, and in extreme cases the vine dies. In terms of frequency, however, the damage is rather minor.
The far more devastating effect occurs indirectly through the transmission of dangerous viruses. The species Xiphinema index (only found on grapevines ) and Xiphinema vuittenezi transmit the grapevine fanleaf virus (GFV), the species Xiphinema diversicaudatum the Arabis mosaic virus (ArMV), both of which cause twig disease. The main preventive measure is the use of nematode-resistant vine rootstocks. These include the American species Vitis acerifolia, Vitis champinii, Vitis cinerea and Vitis mustangensis. Control by nematicides such as DBCP (dibromochloropropane), which was common in the past, is no longer permitted in viticulture.
As a beneficial insect in the vineyard
However, nematodes can also be used as beneficial inse cts within the framework of biological plant protection. There are special preparations for certain plants or pests, such as the pine weevil and owl caterpillars. One sachet can contain up to 2.5 million nematodes. The preparation is dissolved in water and sprayed. The live nematodes spread in this way actively search for the larvae or caterpillars in the soil, attack them and cause them to die within a very short time. See also a list of all pests under vine enemies.
Graphic: By Uwe Gille - Own work, CC BY 2.5, Link
(modified by Norbert Tischelmayer - May 2019)
Nematode: By Agricultural Research Service, Public domain, Link
Largemouth weevil: www.re-natur.de
