Pest and Disease Management in Market Gardening

Technical articles - Diseases

Market gardening Market gardening Soil regeneration

The work of John Kempf shows that the plant first produces simple sugars and then, if it needs to defend itself and is well nourished, it produces increasingly complex carbon chains: proteins (level 2), lipids (3), and secondary metabolites (4: essential oils and tannins).

Many questions arise regarding the issue of diseases and pests :

• Should we fight or coexist?
• What is their ecological role?
• Are they a sign of imbalance?
• Why is this balance broken?
• How do the predators of the pest develop?

Physiological approach

Since it has been demonstrated that the use of powerful insecticides and/or fungicides is harmful to soil biodiversity and therefore contradictory to the development of good self-fertility, it is necessary to approach the question differently.

To guide us, the work of Olivier Husson shows the importance of the plant's health status, measurable by pH and redox potential, on pest development.

The figure below shows the pH-Eh zone of pathogen development and plant balance. John Kempf shows that the plant first produces simple sugars and then, if it needs to defend itself and is well nourished, increasingly complex carbon chains : proteins (level 2), lipids (3), and secondary metabolites (4 : essential oils and tannins). Proteins are difficult to digest by larvae and sucking insects. Lipids protect against bacteria and oomycetes (such as late blight). Essential oils and tannins provide resistance against nematodes, viruses, beetles, and fungi. Kempf thus describes the natural defense mechanisms of plants from a different perspective.

Thus, Olivier Husson and John Kempf explain that it is possible through good plant nutrition to prevent pest development. Poor plant health can be measured by : its pH, its Eh redox potential, and mineral deficiencies (foliar measurements by Novacrop - 20 €).

Significant work remains to establish the reference values of good health (pH, Eh, minerals) for each vegetable. The methodology and management of plant health are now validated for other crops such as rice, wheat, or rapeseed.

pH-Eh zone of pathogen development and plant balance. See Redox Potential.

Management strategy

To prioritize the market gardener's action, we propose a management approach in the following order :

1. Have well-nourished soil for well-nourished and therefore resistant plants (cf Husson and Kempf)
2. Create a balanced ecosystem (grass strips, hedges, ponds).
3. Understand the needs (food and habitat) of pests and respond accordingly.
4. Set a reasonable loss threshold (about 15%) and accept damage below this threshold.
5. React in case of emergency.

The market gardener can lose a lot of time if he does not react : replanting several times a series of lettuces or cabbages eaten by slugs, letting late blight develop on tomato without taking preventive measures (see below), or seeing Colorado potato beetles completely destroy the foliage of potatoes.

The difficulty of pest management is therefore to react proportionally to the damage it can cause : accept its presence if it is not very aggressive but actively react if the risks are too high; experience will play a major role here.

Preventively, the use of natural products has a significant impact on pest management, however, if an economically important crop is heavily attacked, the timely use of more powerful products can curb proliferation and save the crop despite the side effects caused.

Pests	Favorable development conditions	Simple management method
Fungal diseases
Tomato late blight	Plant imbalance. Excess moisture AND coolness	Good ventilation, reduced watering, pruning in drying conditions. Whey spraying.
Late blight on cucurbits	Fragile plants. Moisture on leaves.	Spraying only if drying weather. Curatively, unfortunately only copper works.
Botrytis and Sclerotinia	Too humid conditions, fragile plants	Ventilation of shelters, reduced planting densities
Powdery mildew	On cucurbits, heat and high relative humidity, without free water	Misting, sulfur, bitter orange essential oil
Verticillium wilt	Unbalanced plants Keep moist and not too ventilated to reduce climatic demand.	Preventive : grafting on certain species.
Aerial pests
Cabbage white, or caterpillars in general	Poor nutrition of cabbage	Net if possible, Bacillus thuringiensis (BT) curatively on young individuals
Tuta Absoluta on tomato	Unbalanced plants?	Combination of methods : traps, pheromones and auxiliaries
Carrot fly	High pressure except on Blood Red variety	Net from sowing until the end of flights (September).Varietal selection
Leek fly	Fly present but minor damage if leeks are healthy	Net during flight period (August to November)
Colorado potato beetles	Develops if no rotation	Handpicking with shovel and brush, managed by rotationsor spraying of Bacillus thuringiensis (BT)
Flea beetles	Dry weather and fragile seedlings at early stages	Net from sowing, garlic decoction
Aphids	Plant imbalance	Ladybugs intervene quickly in a rich ecosystem. Spraying black soap, garlic or bitter orange essential oil
Mites	Dry and hot	Maintain humidity, release of auxiliaries, curative treatments, bitter orange essential oil
Thrips	Hot and dry	Misting
Green stink bug on tomato	Under greenhouse	Net at greenhouse entrances, no effective chemical treatment authorized in organic farming
Soil pests
Wireworms & craneflies	Excess water and/or poorly aerated organic matter	Aerate with living plant cover Chickens short term
Nematodes	Soil poor in organic matter, low organic farming	Input of energetic organic matter
Others
Slugs	Humid weather and lack of food	Use anti-slug (Ferramol or Sluxx especially in humid conditions), provide fresh food to slugs, presence of livestock animals.
Voles	Few predators due to weak ecosystem	Cats short term, destruction of burrows with tools, chicken coop
Woodlice	Lots of wood or compost not moistened and lack of water	Fresh food, moisten the soil

Pest sheets

Vole

• Presentation : The terrestrial vole (or mole rat) is a stocky rodent with a short, furry tail and very small ears. It is a burrower (digs holes or tunnels).
• Habitat : It lives in underground tunnels (sometimes borrowed from moles) and is attracted to permanent grasslands on agricultural surfaces.
• Feeding : It is vegetarian and eats every day its equivalent in weight of vegetable roots or fruit trees. It causes significant damage on the farm, especially to potatoes.
• Predators : weasel, stoat, grass snake, viper, eagle, buzzard, hawk, fox, chicken, domestic cat, owl, polecat, wild boar, heron.
• Characteristics and key figures : It lives about 2 years and has an impressive reproductive potential, up to 100 young per pair per year.
• Management method : Regulation is aimed for by predators, weasels, birds of prey, reptiles, foxes and cats.

Flea beetle

• Presentation : Small jumping beetle about 2 to 5 mm, dark colored.
• Habitat : Nicknamed “ground fleas”, they proliferate in tilled and crusted soils, where they love to lay eggs.
• Feeding : Larvae negligibly consume roots then adults feed on leaves. The flea beetle attacks many crops, especially brassicas like turnips or cabbages; some flea beetles attack potatoes. Their attacks are especially problematic for young plants.
• Predators : Birds (tit, robin), toad, ground beetle, lacewing, ladybug.
• Characteristics and key figures : Flea beetles are mainly active in May and June.
• Management method : Installing a net from sowing is advisable.

Carrot fly

• Presentation : Dipteran whose adult measures 4.5 to 6 mm with mainly yellowish head and black body. Mature larva measures 7.0 mm and has a spindle-shaped cream-white body.
• Habitat : Apiaceae crops.
• Feeding : Females, guided by odors, lay eggs in the soil nearby then, after hatching, larvae parasitize roots which become more susceptible to rot.
• Predators : Poorly documented, ground beetles and rove beetles.
• Management method : Specific nets for the carrot fly are the best protection. Installed from sowing until the end of flights around September-October. Resistant varieties (Blood Red) can also be favored.

Leek fly

• Presentation : The adult is a small grayish fly about 3 mm, with a yellow forehead and underside of the abdomen. The larva is pale yellow and about 6 mm.
• Habitat : Allium crops.
• Feeding : The female feeds by sucking sap, causing white punctures on foliage. She lays eggs in outer leaf tissues and larvae mine the green part and the stem.
• Predators : Poorly documented, hoverflies and micro-wasp parasitoids.
• Characteristics : For leek, the first flight occurs between April and June. The second between August and November.
• Management method : Place nets, avoiding contact with foliage during flight periods, i.e., late winter and autumn. It is not necessary to keep nets during the winter harvest period. Many market gardeners do not use nets because the fly only causes superficial damage requiring removal of a maximum of 3 leaves.

Slug

• Presentation : Terrestrial pulmonate gastropod without external shell. The most common species are the slug, the horticultural slug, and the large red slug. Active in the top centimeters of soil, the slug is often very voracious and thus troublesome for crops.
• Habitat : Active in the top centimeters of soil, it mainly comes out at night around 18°C and needs moisture to produce mucus and move.
• Feeding : Very varied, mainly plant tissues (especially damaged plants) but also fungi or animal waste. It ingests 30 to 40 times its own weight in 24 hours. They especially like lettuce and young plants.
• Predators : Toad, slow worm, staphylinid beetle, song thrush, duck, chicken, goose, firefly, hedgehog, ground beetle.
• Characteristics and key figures : Under ideal conditions, a slug can live up to 18 months. Its reproduction period is autumn and spring.
• Management method : Use of molluscicides authorized in organic farming is a good compromise between effectiveness and labor time : Sluxx and Ferramol whose active ingredient is ferric phosphate. The presence of certain livestock animals may be a solution (rooster, duck).

Colorado potato beetle

• Presentation : Beetle about 1 cm long, recognizable by its yellow elytra striped with black.
• Habitat : Able to fly hundreds of kilometers, it covers large areas. Adults hibernate in the soil (25-40 cm deep) and emerge in spring, after the first rains, when temperatures approach 14°C.
• Feeding : It is phytophagous and mainly consumes solanaceous plants. Also called the potato beetle, it preferentially attacks this crop, devouring leaves, stems, and tubers. Adults can eat 10 cm² of leaves per day.
• Predators : Ground beetles and rove beetles for larvae. Birds, shrews, hedgehogs, grass snakes.
• Characteristics and key figures : The Colorado potato beetle reproduces very quickly; a female can lay up to 2500 eggs which hatch after 10 days into very voracious larvae. It lives between one and two years.
• Management method : Respect crop rotations that hinder them and especially pick them up with a shovel and brush.

Aphid

• Presentation : Small insect, winged or not, 1 to 3 mm. Lives in dense colonies and is active as soon as temperature reaches 5°C.
• Habitat : Lives on plants. Some aphid species develop on a single host plant, others are migratory. Winged aphids, attracted by plant colors, enable colonization of new plants to settle.
• Feeding : Sucks plant sap to extract necessary nutrients. Particularly likes sap rich in soluble substances present in young plants and vegetables with unbalanced nutrition. Aphids attack many crops such as tomatoes, zucchinis, cucumbers, eggplants, melons, or beans.
• Predators : Ladybugs, hoverflies, bugs, wasps, spiders, ground beetles, lacewings and various birds (blue tits and great tits).
• Characteristics and key figures : An aphid lives one or two months. It multiplies rapidly alternating sexual reproduction and parthenogenesis : in one year, a single individual could produce 600 billion.
• Management method : Well-established biodiversity nearby is a good management method. Additionally, spraying black soap and garlic can be used.

Late blight

• Presentation : These are cryptogamic diseases caused by different species of pathogenic oomycetes depending on host species. These diseases manifest as brown spots or a white, cottony mold appearance.
• Habitat : The disease develops mainly in humid conditions and at temperatures above 17°C : greenhouse crops, especially tomato and other solanaceous plants, are its preferred targets.
• Feeding : Parasite of the host plant.
• Characteristics : The risk is mainly for solanaceous and cucurbitaceous plants.
• Management method : The year 2021 was particularly difficult for many market gardeners facing late blight on tomato, however some, thanks to adapted measures, were able to ensure a sufficient harvest : respect rotations for sensitive crops, select resistant varieties, promote good ventilation of crops (shelters, soil watering, air circulation between plants), reduce watering during rainy periods, maintain plants (pruning, harvesting, defoliation) in good weather conditions with destruction of crop debris and affected plants. Especially preventively, the use of manure, decoctions, and essential oils can yield results (diluted goat whey, horsetail manure, rosemary cineole essential oils). If the disease develops worryingly, the use of fungicides such as Bordeaux mixture can curb the disease (beware of significant side effects). Good feedback has been given for goat whey diluted half with water sprayed on leaves to strengthen tomato immunity.

Wireworm

• Overview : Beetle with more than 8000 species. Those with a long cycle live 5 years, including 4 years as yellow larvae; those with a short cycle live 2 to 4 years.
• Habitat : Adults are attracted to legumes and grasses. Meadows thus constitute an ideal egg-laying site. Eggs are laid in the soil, especially if rich in organic matter, where the future larvae live and move vertically. They can go as deep as 60 cm.
• Feeding : It is in the larval form that the wireworm causes the most damage. It is polyphagous and attacks many plants, notably tubers and root vegetables, but also lettuce, which it attacks at the root.
• Predators : Mole, shrew, ground beetle, birds, chicken.
• Characteristics and key figures : The wireworm develops mainly in summer. Humidity and poorly aerated organic matter favor the appearance of larvae.
• Management methods : The presence of chickens can solve the problem in the short term. A dense vegetative cover that aerates the soil can be recommended.

Crane fly

• Overview : Known as the “daddy longlegs,” it is a dipteran resembling a huge mosquito.
• Habitat : Its larva, a “grey worm”, develops underground, preferably in cool soils, and comes to the surface after winter.
• Feeding : The larva consumes fine roots of plants, particularly young plants, lawns, flower meadows, but can also attack rhizomes and other tubers, reducing the efficiency of the root system.
• Predators : Chickens, hedgehogs, frogs, moles, birds, ...
• Characteristics and key figures : The crane fly develops mainly in summer. Humidity and poorly aerated organic matter favor the appearance of larvae. A female lays 300 eggs each time she lands on the soil.
• Management methods : A dense vegetative cover that aerates the soil can be recommended and limiting watering which favors their molting.

Cabbage white butterfly

• Overview : Butterfly with white or yellowish wings, varied with black such as the cabbage white, whose caterpillar is harmful to various types of cabbages.
• Habitat : Present everywhere, even in cities, the cabbage white especially likes crucifers as host plants, but also nasturtiums. Its eggs are laid on the underside of the food leaves, in batches of 20 to 50 units. The caterpillars then remain on the leaves before leaving to pupate.
• Feeding : The caterpillar feeds on peripheral leaves. It is mainly troublesome because it causes an accumulation of droppings in the folds and crevices of the plant.
• Predators : Hoverfly, lacewing, wasp, gastropods, birds (tit), parasites (Apanteles glomeratus, Pteromalus, ichneumon, tachinid fly).
• Characteristics and key figures : Up to 3 generations per year.
• Management methods : Nets are preferred and in case of outbreak, they are crushed by hand. When the system is balanced, netting is not necessary.

Cutworm

• Overview : Nocturnal moth. The 750 species in France are divided into two main families : soil-dwelling and defoliators. The caterpillars, gray, measure 5 cm long.
• Habitat : For soil-dwelling species, larvae live on and in the soil, moths are sedentary. For defoliators, larvae develop on the foliage of vegetable crops and moths are migratory.
• Feeding : Cutworms are mostly polyphagous. Very voracious at the caterpillar stage, defoliators attack foliage or fruits, soil-dwellers attack the collars of crops.
• Predators : Blackbird, crow, tit, mole, ground beetle, bat, chicken, parasitic nematodes.
• Characteristics and key figures : Caterpillars overwinter and develop in March-April. Larvae appear from June to July. A female lays between 800 and 1200 eggs and there can be two generations, especially during dry and hot summers.
• Management methods : As soon as you observe the first damage, look for larvae in the soil within a 20 cm radius around the plant using a knife and destroy them. Attacks are rare with healthy soils.

Mite

• Overview : More precisely Tetranychus urticae for pest mites, these are tiny arachnids.
• Habitat : Particularly present in dry and warm environments, such as for solanaceous and cucurbitaceous crops under cover.
• Feeding : Mites pierce the leaves on the underside causing drying of the foliage and the entire plant. In severe cases, the plant is covered with webbing and fruits are depreciated.
• Predators : Certain mites and beetles.
• Management methods : Biological control is complex because the development of auxiliaries in dry and warm environments is difficult. However, maintaining humidity, releasing auxiliaries, and using treatments in curative mode can solve the problem.

Promoting the emergence of an agroecosystem for holistic pest management

As can be seen with the various techniques implemented within the MSV Normandy network, many market gardeners rely on the action of other species, such as ladybugs, cats, or even birds of prey, to counter pest attacks. The main enemies of crops are indeed insects and rodents. However, these have many enemies among microorganisms, mammals, birds notably birds of prey, amphibians, and even insects. Thus, in order to self-regulate pests and predators, it seems desirable to promote biodiversity on the farm. For this, predators must establish themselves permanently on the farm, which requires long-term work, as some populations may take several years to settle.

Market gardening on a small scale, characterized by polyculture (diversity of resources and shelters), and on living soil (rich in food resources and stimulating biological activity) with limited use of pesticides (especially those with non-targeted action), already promotes biodiversity in its system. However, crops do not favor the sustainable establishment of populations, as they have a defined growing period. It is therefore necessary to maintain natural habitats around crops, so that predators find the resources necessary for their survival. This will allow them to be present and active from the beginning of spring, at the appearance of the first pests. Some arrangements that can improve biodiversity presence on the farm :

• Flower strips : They are composed of perennial or annual flowers. It is preferable to offer a diversity of structures and foliage but above all to guarantee a constant availability of nectar and pollen, by choosing flowers according to their flowering period to create a succession. The spaces must not be isolated; it is best to plan fairly wide strips (2-6 m) connected to each other.

• Hedges : To make them even more attractive, select flowering tree and shrub species, as well as some fruit trees for birds. It is important to present a diversity of species, about 10-15, with different forms and foliage. Moreover, it is relevant to ensure ground cover by herbaceous plants.
• Shelters : It is possible to easily build or obtain birdhouses or even bat roosts. Similarly, piles of dead leaves, branches, or rocks make excellent biodiversity hotels. The goal is to offer new refuge sites to wildlife. Perches can also be installed to attract birds of prey, which will thus regulate rodents.

• Ponds : Nothing better to provide water to local wildlife and welcome amphibians. Ponds can be temporary or permanent, depending on the market gardener's wishes. Ponds and ditches temporarily filled with water are key to hydrating the ecosystem throughout the year.

Cet article est tiré du Guide MSV 2022.

Retrouver les autres chapitres du livre ci-dessous :

• Démarrer en maraîchage sol vivant
• Le cycle de la fertilité des sols
• Les vers de terre dans l'écosystème sol
• Diagnostic de son sol
• Stratégie de gestion de la fertilité
• Réaliser son bilan humique
• Gérer l'enherbement en maraîchage sol vivant
• Gestion des maladies et des ravageurs en maraîchage
• Conditionnement et conservation des légumes
• Commercialisation et transformation en maraîchage
• Produire ses propres semences
• L’installation en MSV
• Conversion en MSV
• Jardin amateur
• Verger maraîcher
• Avoir un atelier poules pondeuses
• Introduction aux itinéraires techniques
• Conseils de maraîchers sol vivant