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March 2006. In New Caledonia, the roots of guava trees are infestated with Meloidogyne sp. Therefore, galls and abnormal roots are observed as well as the decline of the entire tree. Fungal infections of Fusarium moniliforme and Botryodiplodia theobromae also occur, but Meloidogyne sp. is the primary cause of the decline. Several questions were asked:
- Are there resistant (or tolerant) root stocks to Meloidogyne spp.
- What type of crop rotation would help to reduce the Meloidogyne population
- The address of the institute that could identify the Meloidogyne species on the guava
- What chemical treatments can be used?
There has been research on Meloidogyne spp. on guava in Venezuela. Good results are also reported from Mexico against Meloidigyne javanica on guava using Furadan (carbofuran) at 250 to 300 gms of the commercial product per tree. But be careful when handling it. Alternatively, prepare a plot totally free of all live plant material for 6 or 8 weeks, and then plant it with guava raised in sterile soil. Meloidogyne spp. can’t survive for long without living plant material to feed on.
Root-knot nematode is also an important problem in Palau. Woodashes are used, mixed with the soil before planting or diluted with water (a handful to a gallon of water), and also applied once a month in water during the dry. In addition, each tree is given a handful each month, but be careful not to put it too close to the trunk. Using charcoal in the same way, was also said to be effective.
A long term solution is to use biocontrol agents, such as Paecilomyces lilacinus and Pochonia
chlamydosporia (formerly Verticillium chlamydosporium) singly or in combination, with and without crop
rotation, in vegetable crops. Success comes very slowly, but surely.
P. liacinus (strain Pl-251) is available commercially. This strain is widely adaptable and should help. With
P. chlamydosporia the trick is to find a ‘virulent’ strain locally, which can then be multiplied. At the University of Reading, UK, a technique has been developed whereby bulk production on locally available grain/compost media is possible.
In guava, crop rotation is not an option. Using ‘suppressive’ or ‘non-host’ crops (e.g., sorghum, sesamum, marigold) as intercrops will probably increase the pressure of infestation on the ‘host-crop’, guava. However, it is possible to use a susceptible crop like tomato: any variety without any commercial value will do. The aim is to allow infestation of root-knot on tomato and to remove the seedlings before egg-laying (in about 3 weeks) commences. Try this in a small patch initially, to be sure that it works. In combination with one or more of the biocontrol agents, it will help to manage the situation in the long term.
For an immediate effect on population, Furadan is of great use, as is neem cake (the left over after neem-oil extraction). Members were also remined of the benefits from increasing the organic matter content in the soil through mulching and composting; this can help negate the effect of nematodes simply by improving the availability of nutrients to plants; it is also possible that antagonistic microbial organisms in the compost will reduce nematode numbers.
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