Green manure mixes and nematodes: a risky combination

Sowing green manure crops offers many advantages. Green manures can be used, among other things, to combat certain types of nematodes.  When choosing a mixture of green manures, keep in mind that some crops  can be host plants for harmful nematodes.

Green crops offer many benefits. One of these is the ability to control soil diseases and nematodes. For example, certain varieties of fodder radish and yellow mustard are able to control beet cyst nematodes. Fodder radish is able to disrupt tobacco rattle virus transmitted by Paratrichodorus teres   and reduce the population of root knot nematode Meloidogyne chitwoodi / fallax . The root lesion nematode Pratylenchus penetrans cannot reproduce on Japanese oats and is actively suppressed by the marigold species, Tagetes patula .

If harmful nematodes lead to yield and / or loss of quality, or are not allowed to be present during the cultivation of propagation material, do not sow green manure on which these nematodes can multiply. You actually help these nematodes through the winter. When a green manure is not a host plant, the decrease is equal to black fallow.

Green manure mixture

Sowing a mixture of different green manure crops offers additional benefits: 

• Mixtures increase the diversity of soil life
• Mixtures develop more root biomass 
• Mixtures are often more stress resistant

Known combinations in a green crops mix are, for example, a fast germinating cruciferous variety (suppresses weeds) with a grassy variety (many roots, poor weed suppression). Or a grain (lots of roots) in combination with a nitrogen-fixing legume.

Host plant in mixture

While mixtures have many benefits, a mixture can be detrimental if the goal is to control certain nematodes. Research by Wageningen UR shows that mixtures can lead to the same multiplication of nematodes as a single green manure that is a good host plant for the nematode. Three green manures were sown on a plot with the root lesion nematode Pratylenchus penetrans : Japanese oats, Tagetes (marigold) and a mixture of seven green manures. Some were also kept fallow. 

The study showed that the non-host plant Japanese oats causes a similar decrease to black fallow. An active decrease was measured after the cultivation of Tagetes. However, a much higher population was measured in the mixture containing a combination of host and non-host plants for P. penetrans . This shows that nematodes actively search for their host plant and can multiply on it (see figure 1).

Make the right choice

Mixtures with green crops offer many advantages, but can also result in a strong multiplication of harmful nematodes. When choosing a green fertilizer mixture, it is therefore important to know the situation of the soil. Know which nematodes are present and adjust the green manure (mixture) accordingly. If a mixture is chosen, make sure you know which green manures are occurring and what the host plant status is for the nematodes present. Table 1 provides insight into the host plant status of a number of commonly used green manures. 

Nematode research

Autumn is a good time to conduct nematode research. Eurofins Agro analyzes the living nematodes using DNA research, which means that the nematodes are always identified by species. The chance of detecting the most harmful nematodes is highest in the autumn. This is because root knot nematodes (Meloidogyne) and root lesion nematodes (Pratylenchus) can strongly decrease in numbers in winter. The low numbers in the spring are more difficult to demonstrate, but can multiply quickly and cause problems when a host plant is being grown.

Table 1: Propagation of nematodes per green manure. Source: Aaltjesschem 2020

Legend
 + = little propagation, ++ = moderate propagation, +++ strong propagation, – = active decrease, o = natural decrease. R = breed dependent, i = limited information,? = unknown

More information:

Green manure fertilizer
manual Nematode scheme

Order nematode research

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