Red spider mite

Bioagressor - (Panonychus ulmi) - Pests - Red spider mite

Spider mites are pests that pose a threat to many crops around the world. Despite their small size, they are capable of causing serious damage very quickly due to their high reproductive capacity. There are over 1,200 species worldwide, many of which are common crop pests. The two-spotted spider mite, Tetranychus urticae, is by far the most widespread species in glasshouse crops and in many outdoor crops.

Recognition

Virtually invisible to the naked eye, the presence of the spider mite can be spotted by the tiny light spots on the foliage that spread, turning the leaves yellow or even drying them out in the event of heavy infestation. Fine webs can also be seen at the ends of the plant. Stems and fruit can also be affected.

Specific attacks

Alternative methods of combating red mites in market gardening

Release beneficials in greenhouses

Phytoseiids are predatory mites that consume other mite species at all stages of their development. In particular, we use Phytoseiulus persimilis or Neoseiulus californicus against spider mites orAmblyseius species against the greenhouse tarsonema or theAculops lycopersici. They are highly effective, but can only be released when there are sufficient numbers of prey, otherwise they will not be able to feed.

The Phytoseiulus needs good hygrometry, at least 75%, and a temperature above 20° to be effective. It attacks all stages of development of the spider mite, devouring its tissues. It is best used in midsummer.

Apply between 5 and 20 mites per m², preferably in the evening when it is cooler.

Amblyseius swirskii is used to control the causal agent oftan spot(Aculops lycopersici). It can be used in any season, as it does not go into diapause in winter, but it can only develop between 20 and 22°C.

However, according to a study by Lambion et al (2022), published by the GRAB in 2023, "theestablishment [of phytoseiids] in summer crops is fairly random, and their maintenance, particularly in the height of summer, is fairly rare (absence of prey, climate too dry ?)". The aim of this same study is to "test the value of plant mulch on the soil as a complement to 2 strategies for releasingbeneficial insects, in comparison with a conventional release without plant mulch. The aim was to coincide with the peak presence of the pest (spider mites) and thebeneficials (phytoseiid mites).

After 3 years of trials, Lambion et al (2022) indicated that the addition of buckwheat hulls in fairly narrow strips (25cm on either side of the planting row) resulted in better establishment of Phytoseiid mites, with higher numbers observed in the crop. The maintenance of beneficials is more durable than in the control with plastic mulch, where Phytoseiid populations decline sharply and rapidly after release.

You can find the Lambion et al. publication (2022) by clicking on this link

Drenching plants

Another available lever is drenching. This technique involves spraying fine droplets of water onto and under the leaves. This operation should be repeated frequently (every day or once every two days) to disturb the insects, which will multiply less quickly.

According to a market gardener in the MSV network, combining the release ofbeneficial insects (Phytoseiid mites) with drenching effectively reduces pest pressure.

Another grower advises the use of a curative biosolution : spidex from koppert.