Control of Meloidogyne in intensive organic vegetable production in greenhouse

Organic production is soilborne. This is the basis for organic greenhouse horticulture. That is why organic greenhouse growers pay a lot of attention to soil, both soil fertility and soil health.

By growing the same crops over and over, populations of pathogens build up. These pathogens are often related to one or more plant families. Root knot nematodes are an example of this and occur often in heated greenhouses. Meloidogyne incognita is most commonly found, but M. hapla and M. javanica also occur regularly. The generation time or life cycle of root knot nematodes varies per species and depends on the temperature and the host plant. When populations reach a high level, this can cause the death of more than 50% of the plants, and even with lower populations, there will be a serious decrease in yield.

The cause of the problem with root knot nematodes in soil-bound greenhouse fruity vegetable production is in the first place the very tight crop rotation of tomatoes, peppers, cucumbers and aubergines. Especially in heated crops the soil hardly gets time to recover but a broader crop rotation is hardly possible from economic point of view: the expensive infrastructure requires an intensive cultivation method.

Possible control measures such as the use of resistant varieties or soil disinfection are inadequate. Resistance is present in certain crops (including tomato) but this is often incomplete. Soil steaming disturbs the soil and destroys natural resistance.

Using a catch or antagonistic crop to lower the population of nematodes seems more appropriate. However, such crops are not easy to find. In addition, crops with a short growing period, in which quick effects can be seen, have to be economically feasible. Another option is the use of natural resources that work on a vital soil resistance and/or have an (in)direct effect on the existing nematode population.

The objective of the project is to ensure a future for the cultivation of fruity vegetables in organic greenhouse horticulture by developing an integrated control of root knot nematodes (Meloidogyne spp.) based on innovative cultivation techniques. The primary target group are specialized organic fruity vegetable growers in greenhouse in Flanders. In addition, we focus on outdoor organic vegetable  growers, producers of plants (rootstocks and seeds) and natural resources (compost, biocontrol organisms), advisors and the government.

We want to achieve this goal by focusing on:

• Increasing the knowledge of Meloidogyne in fruity vegetables.

• Finding rootstocks of tomato, pepper and cucumber with sufficient resistance levels against different Meloidogyne spp, which also deliver acceptable yield and quality

• Development of alternative cultivation techniques such as cultivation schemes with short intermediate crops to control Meloidogyne

• To gain insight into the effect of organic additives on Meloidogyne populations

• To gain insight into the effectiveness of natural remedies against Meloidogyne populations

• Individual advice and knowledge transfer

Before the start of the project, it was unclear how best to tackle root knot nematodes in heated greenhouses. During the project, it became clear that a combination of different techniques gives the greatest chance of success. These include (1) using resistant rootstocks, (2) incorporating intercropping during or after fruity vegetable crops, and (3) applying chitin-rich material to the soil.

From the rootstock trials conducted during this project, TRC11550 and Ancora seemed the most promising rootstocks for cucumber. For tomato, the rootstocks Fortamino and DRO 141 TX are the favourite rootstocks in the fight against root-knot nematodes, while for sweet pepper these are the rootstocks Taritana and Scarface. Many organic greenhouse growers changed their choice of rootstock in the course of this project due to the knowledge gained. Growers who were still using Maxifort as a tomato rootstock indicated that they would definitely no longer do so in the future because of its strong nematode increasing effect.

In the search for a suitable crop in the winter period, several crops were evaluated: rye, wild rocket, mustard leaf, corn salad and a mixture of 14 varieties. Rucola showed promising results in a first trial to control the nematode population. The trial was repeated which also looked at the effect of destroying and incorporating the crops in the soil. When the crops were not incorporated, a decrease in nematode population was seen in rucola and leaf radish. After crops were incorporated, a stronger decrease was observed in leaf radish and a slight decrease in mustard leaf, although final populations remained quite high everywhere. During the project, several growers have already switched from fallow greenhouses during the winter period to growing a winter crop such as rucola, leaf radish or mustard leaf.

 The possibility of controlling nematode population infestation using intercropping was also explored. Leaf radish, Tagetes patula, Ageratum houstonianum,Cineraria maritima and roller clover were sown under peppers in the double planting row and stem onion, basil and aubergine MAO were planted under/between peppers. Intermediate crops sown or planted between the main crop of fruity vegetables can attract root-knot nematodes more strongly than the main crop, thereby protecting the latter better. They can also act as catch crops, "trapping" the nematodes in their roots. The disadvantage of these intermediate crops was that some such as aubergine, Tagetes, leaf radish and Ageratum had a higher growth rate than the peppers, requiring regular pruning back

The intermediate crops were also found to create a humid microclimate that caused Sclerotinia to develop in the peppers. It is therefore important to choose an intermediate crop that maintains airiness at the stem base to ensure the crop health of the main crop. An additional pot test provided conclusive information on the influence of the intercropping on the nematode population. Most intermediate crops give rise to egg packet formation, with the exception of Tagetesand floss flower (Ageratum). However, in the case of floss flower, it is not yet known whether nematodes are attracted here or not. Tomato, basil and stem onion show egg packets in all plants and also the most eggs per egg packet, so these are not recommended as intermediate crops. Given the possible risks involved in intercropping, not all growers were convinced. However, some of the organic greenhouse growers strongly believe that the benefits of intercropping outweigh the possible risks involved. Tagetes and floss flower are the crops sown under peppers and tomatoes at a number of growers nowadays.

 Several natural soil products were tested in a tomato crop at an organic grower with Meloidogyne infestation. These included CMC and worm compost produced by the grower himself, as well as compost from ILVO. The products chitin and Rootella were also in trial. Rootella inoculates plant roots with endomycorrhiza.Endomycorrhiza improve nutrient uptake, thereby increasing crop yield and reducing stress. Chitin was shown to have a reducing effect on Meloidogynein previous research. The Meloidogyne population increased in all objects during tomato cultivation, due to the use of the non-resistant rootstock Maxifort. Where Rootella or chitin had been applied, this increase was less, while CMC compost actually increased the nematode population the most. A similar trial was laid out in a cucumber crop. In cucumber, all objects caused a marked reduction in nematode population, with the strongest reduction where chitin was applied. There is no clear evidence that applying compost at a dose of 3kg/m² or Rootella are ways to reduce nematode numbers. Some growers indicate that based on the results from these trials, they are convinced of the positive effect of chitin-rich material. Products such as Protix and Servasan currently are applied before and during cultivation on a number of farms.