Nets insect-proof

Without crop rotation, there is little point in using these nets, especially if you are installing protection for the first time over soil that has already received infected root vegetables. Inside the covers, when the pest pulps buried in the soil produce adults, they will be protected from their own predators. Any weeds that are thought to harbour pests should be removed from the plot where the protection tunnels will be installed. The cleanliness of the soil is essential to reduce the risk of polyphagous pests appearing inside the protections. This is for example the case of radishes which will still take the maggot if field mustard is present on the ground before the installation of the nets.

For the same reasons, the addition of organic matter is only possible if it does not contain the pulp of a bio-pest; for this, it is necessary to spread refined compost that has undergone a thermophilic phase (see the article on the production of hot compost). Other more or less useful insects whose larvae overwinter in the soil may also appear inside the nets.

Insect nets are all the more useful as some insects have become resistant to certain pesticides. For example, onion and carrot flies are often resistant to chlorinated insecticides. Most registered insecticides that can destroy root vegetable pest eggs and larvae are reserved for professional farmers because of their toxicity. Anti-insect nets thus make it possible to avoid using these phytosanitary products.

These nets allow air and light to pass through and allow watering by sprinkling. Do not buy nets from an internet site if the mesh size is not known. These nets should be wide enough to be held in place by 2-metre hoops so as not to compress the leaves too much. Drip irrigation can also be introduced inside the nets.

Noctuid moth on insect netting to protect carrots

The price and quality of these nets vary greatly from one supplier to another. Some nets have thicker wires than others, which does not guarantee that they are stronger. An anti-insect net must be strong and light (resistant to the clips on the hoops), transparent (the plants inside the protection must be visible) and allow water to pass through easily and avoid excessive temperature rise inside the protection. The mesh size should be regular. Some nets can be reused for several years after deleting any small holes. These openings appear from time to time and can be filled with a drop of PVC glue known to be waterproof, which is available in all DIY shops. This glue does not adhere to the fibres; it seals the small holes by trapping the fibres to form a sufficiently strong and watertight structure. The origin of these small openings is often accidental due to handling by the grower, or caused by animals such as cats, or possibly insects and other animals that try to get inside the protection.

Here is an internet address that I highly recommend where you can get very good quality insect netting as well as bows and fixing clips; click here

It is preferable to use Biotex insect-proof netting - 40gr/m² which has a minimum life span of 3 years.

Note that some growers use anti-insect nets without hoops and placed directly on the crops; more information by clicking here

The celery fly (Philophylla heraclei) is 5 to 6 mm long and the female lays about 150 eggs in small groups on the leaves. The larvae develop in 25 to 30 days. They form excavations that form white spots called mines. The excrement shines through between the two epidermis of the leaf. In the event of a major attack, the larvae dig galleries in the petioles. The first generation of flying adults appears in May and the second in June-July. The nets can be removed around 15 August, but this exposes the celery to carrot flies.

Carrot cultivation under insect netting.

The carrot fly maggot (Psilia rosae) is a serious pest of vegetable crops. The adult is 4 to 5 mm long. The eggs are invisible, isolated or clustered in the soil. The larvae dig galleries in the roots, making them unfit for storage. This pest is polyphagous and can migrate to other vegetables such as parsnips, celery and sometimes parsley. The pulp overwinters in the soil near the cultivated plots it has invaded. The first generation emerges in spring in a staggered manner until July. A second generation emerges from September. There may even be a third generation in autumn. In the Provence-Alpes-Côte d’Azur region, carrot foliage can be attacked by various moths, including the very polyphagous Spodoptera littoralis (Spodoptera exigua).

In winter, carrots keep very well in the field if they are protected from frosts by a cover of straw or lawn mowing. In the Provence-Alpes-Côte region, I have sometimes seen carrot flies emerge in the middle of winter on sunny, warmer days. In the weeks that follow, the roots are invaded by larvae. For this reason, insect netting should not be removed in the autumn and winter until the carrot harvest is complete.

Note that adults of Spodoptera littoralis feed on pollen and nectar and can be found in hedges, especially when they are provided with floral species (such as the oleander, which is very common in the Provence-Alpes-Côte d’Azur region). Abandon all the medieval infusions proposed here and there based on nettles, wormwood, tansy, fern... whose effectiveness is null. Only anti-insect nets will ensure an effective protection during the whole growing period.

A few adult moths may appear under the anti-insect nets, for example from pupae accidentally introduced during compost spreading or from a previous unprotected crop, from egg-laying on the nets and introduction of the larvae through an accidental opening... As the caterpillars are not always visible through the nets, predation is most noticeable when the flying adult tries to get out of the protection. The crop should then be inspected. If defoliating caterpillars are present, an attempt can be made to destroy them by spraying with esterified rapeseed oil, unless you have introduced ladybirds for aphid control (see below: important recommendations). When the carrot plantation is not very large, which is often the case in home gardens, the moth larvae, which are often few in number under the insect netting, can be destroyed by hand.

Growing leeks and other alliums under insect netting.

Leeks and onions are often attacked by the larva of a butterfly, the acrolepiopsis assectella (Acrolepia assectella), or other moths such as the ipsilon (Agrotis ipsilon aneituma) and the harvest moth (Agrotis segetum), which can also be found on sugar beet, potatoes and cereals.

All alliums are threatened by the acrolepiopsis, also known as the leek moth, which can be confused with two other leek bio-agressors: the leaf miner and the onion fly. As far as the leek moth is concerned, the adult moth appears in April-May. The females lay eggs on the leaves of the host plant and then burrow into the stem to form galleries. The caterpillars in turn become adults that will lay new eggs between June and mid-August. Depending on the weather conditions, a third generation can occur between the end of August and the end of September. The leafminer has caused particularly serious damage since its arrival in France.

The onion fly (elia antiqua) is a diptera measuring 5 to 6 mm in length which has the particularity of producing maggots that like the base of roots and leaves. Bacteria settle in the galleries, causing tissue rot. Up to 5 generations can be observed during a growing season.

Alliums are sometimes attacked as early as April - May by the "onion criocene", a beetle that is very recognisable by its red colour. From June, the larvae devour the leaves.

In the Provence-Alpes-Côte d’Azur region, as in the entire Mediterranean region, the brachicera weevil, which affects garlic, but can also attack other bulbs, is rife from May onwards.

In the absence of protective netting, it is very difficult to protect alliums against all these bioaggressors. To avoid the use of pesticides, some amateur gardeners use diluted bleach, which is just as toxic for the soil's biodiversity as chlorinated pesticides, which have been banned in France.

Growing radishes under insect netting.

Radishes are very often attacked by the maggot of a fly (Phorbia floralis) which digs galleries in the roots. Within 15 days, the radishes become unpalatable. For this reason, the cultivation of radishes is often abandoned by amateur gardeners who do not wish to protect their crops with an insecticide. They are not wrong for two reasons:

Radishes have a short crop cycle and a curative treatment with an insecticide is always problematic. The choice of insecticide, the timing and the way it is applied is a matter for a professional.

The use of synthetic or organic insecticides has become obsolete, as it is very easy to protect radish crops with insect netting. It is probably one of the plants that is best protected with insect netting. With this type of protection, you will find that radish cultivation has become an easy crop without any losses, regardless of the variety. As with all other vegetables protected by insect netting, the absence of pests inside the protection does not prevent crop rotation.

Growing lettuce under insect netting.

Root vegetables are not the only plants that can be protected by insect netting. All vegetables that do not need to be pollinated can be protected by insect netting. This is the case for all varieties of lettuce. These are often attacked by caterpillars of moths (defoliator moths), especially the Autographa gamma caterpillar, which is a moth; its light green caterpillar devours the salad leaves.

Salads are frequently victims of several species of aphids such as Nasonovia ribisnigri, commonly known as the lettuce aphid. These aphids can easily pass through insect netting when the mesh size is 1 mm. Some aphid predators should be introduced to neutralise these attacks (see article: Importing beneficial insects against aphids).

Other aphids attack salad roots (lettuce aphids lanigères). The damage is not very visible and is characterised by a reduction in the growth of the plant. Root damage is most noticeable when the lettuce is pulled up with its roots. Many yellowish-white insects are found along the roots. These insects have a conspicuous tuft that looks like a woolly coat. This aphid is also able to transmit the lettuce mosaic virus.