Insect nets for crop protection

Growing turnips under insect netting

Insect netting is effective in controlling flea beetles, which produce small holes in the leaves. They also prevent the settlement of the Delia radicum maggot, which is also present on crucifers and radishes. The first damage appears mainly in May. Flea beetles are small beetles that find shelter in grass and wild crucifers. For this reason, all weeds must be removed from the area where the insect netting is to be installed, otherwise the protection will become a flea beetle farm, protected from their predators. Insect netting is necessary throughout the crop to provide particularly effective protection against these devastating pests without using a single drop of organic or synthetic pesticide.

It should be noted that flea beetles may appear in shelters if turnips in pots have been grown in the open air. Flea beetle eggs are very small and cannot be detected. It is best to sow turnip seeds directly under cover.

Celery cultivation under insect netting

Céleris raves protégés par un filet anti-insectes

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

Les légumes racines ne sont pas les seuls végétaux qui peuvent être protégés par des filets anti-insectes. Tous les légumes qui ne nécessitent pas d’être pollinisés peuvent être protégés par ces voiles. Et c’est le cas de toutes les variétés de salades. Celles-ci sont souvent attaquées par des chenilles de papillons (noctuelles défoliatrices) surtout la chenille de l’Autographa gamma qui est un papillon de nuit ; sa chenille de couleur vert clair dévore les feuilles de salade.

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).

D’autres pucerons attaquent les racines de salades (pucerons lanigères de la laitue). Les dégâts sont peu visibles et se caractérisent par une réduction de la croissance du végétal. C’est surtout durant l’arrachage des salades avec leurs racines que les dégâts racinaires sont observés. On découvre alors de très nombreux insectes blanc-jaunâtre le long des racines. Ces insectes portent une touffe assez bien visible ayant l’apparence d’un lainage. Ce puceron est aussi capable de transmettre le virus de la mosaïque de la laitue.