Biological control of root knot nematodes in organic greenhouse horticulture remains difficult
A simple, straightforward technique or method for effective control of root knot nematode problems in organic greenhouse horticulture is not yet available. This is the message of a research report by the Plant Sciences Group of Wageningen UR.
Photograph: Root knot nematodes are causing root malformation. This prevents the plants from taking up water and nutrients, sometimes causing death.
Techniques and methods such as biofumigation, different cultivation systems and the use of biocontrol agents were compared in the study. According to the coordinator of this research, Andr?? van der Wurff, the solution is ??? for the time being – consisting of a package a measures with growers choosing an approach on the basis of type of root knot nematode, crop, type of holding, and soil composition.
Van der Wurff, who is working for Wageningen UR Greenhouse Horticulture of the Plant Sciences Group: ???Currently, steaming of the soil is seen as the most effective method for controlling root knot nematodes (Meloidogyne species). But this technique has major disadvantages: all other soil life is killed as well and the method requires a lot of energy. This is why the study focused on alternative techniques for restricting the damage caused by nematodes.???
The scientists tested a large number of means and methods for biological control of root knot nematodes. Only boron and some still unauthorised plant extracts showed some degree of effectiveness but none of the products could fully control the nematodes.
The study into biological soil disinfestation showed that withdrawal of oxygen from the soil, by incorporating fresh organic matter, yielded the best predictable results. Biofumigation, by isothyonate gas released after the incorporation of, e.g., cabbage leaves, does not simply lead to predictable results. This is caused by the large effect of, e.g., age of the leaves and cabbage type.
Use of the biocontrol agent Pasteuria penetrans, a bacterium originating from Japan, was found to be effective against various types of root knot nematodes. The study showed the pasteuria bacterium to be effective against the nematode species Meloidogyne javanica and Meloidogyne incognita but it was insufficiently effective against all nematodes. In addition, the use of the bacterium is not yet authorised in the Netherlands.
The use of special cultivation systems can also contribute to controlling root knot nematode problems. The so-called Baijens cultivation system was found to offer good possibilities for the control of nematodes in cucumber cultivation. In this cultivation system the number of cucumber plants of two rows is planted in one row with the plants being separated above the ground. This leaves much wider soil strips between the rows; these can then better be used for measures to control the nematode problems, e.g., by cultivating nematode-controlling plants or biological soil fumigation during cultivation.
Considering all results, the scientists conclude that no ready-made method is available for the organic control of root knot nematode problems in organic greenhouse horticulture. Van de Wurff: ???organic growers will have to analyse their own situation carefully and then choose the best approach, usually involving more than one technique.???