Soil infestations

Biological control of soil infestations

Subjects:
Slug control
Vine wevil control

Biological control is usually associated with the aboveground distribution of natural enemies. Not without reason, really, since the aboveground parts of the plants can be affected by hosts of enemies, the damage is often directly visible, and in hydroponic cultivation, soil-related pests are often unable to access the roots. In the cultivation of soil-based crops, however, the underground parts will equally be exposed to damage caused by harmful organisms. Traditional examples would include molluscs, vine weevil, sciarid flies, nematodes, et cetera. All of these organisms will include one or several stages in their life cycle where they parasitize on the root system of the plants, or even cause damage to aboveground parts. Yet another phenomenon that may occur in soil cultivations, is the increased speed in population build-up of – particularly – leaf miners and thrips. Both these types of insects will naturally complete their pupal stages in the top layer of the soil. Contrary to soil cultivations, in hydroponic cultivations a certain percentage of the pupae will shrivel up on the foil.

Even these soil-related pests find their solution in nature, in the form of their natural enemies. For the pests mentioned above, the solution can mainly be found in a number of beneficial nematodes and a predatory soil mite. The nematodes are real parasites, penetrating the body of their host and reproducing there. The predatory soil mites can feed on the larvae of pest organisms, including, for example, thrips nymphs. These natural enemies to, among others, soil-related pests, are produced by BioPol and commercially applied in cultivations. We will now proceed to introduce these natural enemies to you briefly.

Nema Slug to control slugs

This is a preparation based on the insect parasitic nematode Phasmarhabditis hermafrodita. These nematodes are active in the soil and will gain access to the body of the slug via the pallium, or mantle of the slug. Once they arrive there, bacteria from the body of the nematodes will ultimately kill the slug, but before this happens, the mantle of the slug will typically bloat. Just a few days after infection, the parasitized slugs will stop feeding. The nematodes will feed and reproduce on the dead body of the slug and subsequently set out to find new prey. Nema Slug is effective against the gray fieldslug (Limax agrestis) and related species. Nema Slug should be dissolved in water, and can subsequently be poured or sprayed onto the soil, using a spray or a watering can. Dosages of approximately 300,000 nematodes/m² are the most common, with a repetition after 14 days if necessary. However, the soil should be kept moist until 14 days after application to ensure optimum effect of the nematodes. Nema Slug is most effective at a soil temperature of 15°C (5°C minimum, 20°C maximum).

Heterorhabditis megidis to control vine weevil

Heterorhabditis is an insect parasitic nematode against the larvae of snout beetles or weevils such as the vine weevil. The nematodes actively search the soil for larvae and penetrate them. Here, too, penetration of the nematodes will be followed by the release of bacteria that are lethal to the host. Tissues of the vine weevil larvae will be converted by the bacteria into substances the nematodes can easily digest. The nematodes will procreate and their offspring can set out to find new prey.

Infected larvae will show a discoloration from white to a pinkish red-brown hue, and they will die within a few days. For adequate effect the soil should be sufficiently moist, at a soil temperature between 10 and 25°C. Heterorhabditis as a preparation is dissolved in water, and can be added to the soil using a spray or a watering can. For slight infestations a dosage of 500,000 nematodes/m² will suffice, while more serious infestations will require 1,000,000 nematodes/m². One single application will usually be enough to yield the desired controlling effect.