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==Source==
This article is made using information from the coursebook:
Cultivation techniques </br>
Course from: 1st year of Herbalism</br>
Course year: 2005 - 2006</br>
Education center: Syntra, Asse-establisment</br>
Teacher: Leo Van Crombrugge


===D. Biologically allowable crop protection methods===
===D. Biologically allowable crop protection methods===

Revision as of 15:06, 2 November 2012

Part 4: Crop protection

  • Causers of diseases and pests

Deviations in the crop can be caused by:

  • A. Non-animal parasitic organisms
    • Fungi
    • Bacteria

If an infection is caused by non-animal parasitic organisms, they are called diseases.

  • B. Animal parasitic organisms
    • Nematodes
    • Insects
    • Mites
    • Mammals
    • Birds

If an infection is caused by animal parasitic organisms, they are called pests.

  • C. Non-parasitic causes
    • Soil influences
    • Weather influences
    • Air pollution

These disrupt the physiology of the crop. We talk of physiogenic diseases.

  • D. Weeds

These compete with the crop for water, nutrients, light and space.

A. Non-animal parasitic organisms

Fungi

Fungi are categorised to the lower plants. They contain no chlorophyll and are dependent for their nutrition on dead and living organic matter. They consist of microscopic filaments (hyphae) which are sometimes packed together as a visible tissue (mycelium). Molds propogate mainly trough spores, which are very fine spheres that are dispersed by wind, water and also by animals. With sufficient moisture and warmth, the fungi develop rapidly. The damage that fungi cause is of major economic importance. We currently know some 3000 harmful fungi.

Commonly appearing on plants:

Germing fungi

These can infect the seedlings in the nursery. The disease is also called smoldering. The young seedlings start to melt or fall over. Sometimes the plants don't rise above the soilsurface because the fungus has already struck them at the germination. It is best to hold off with sowing until the soil has warmed and dried enough. Also, do not sow too deep in the soil, nor too close together.

Botrytis

This fungus manifests itself from the soil at humid weather and first targets the dying plant parts of a crop. Then it goes on to healthy plant parts. These will discolorate, and after this, they will exhibit a gray mold fluff, full of fresh spores for a new spreading.

Mildew

With "Mildew", 2 diseases are meant: powdery mildew and downy mildew. Powdery mildew usually appears around the middle of July as woolly spots on top of the leaves. Moments later they are covered with a flour-like layer. The fungus draws moisture from the leaf cells, which makes the leaf discolor brownish and makes it dry-out. With the downy mildew, the symptoms are pale-yellow discolored spots on top of the leaf and white, powdery fungal fluff at the bottom. The leaves discolorate brown afterwards.

Prevention All measures aimed to let the crop dry-up faster, have a preventive effect on fungi. We can provide a wide spacing, a windy and weed-free place and adequate ventilation in the greenhouse. Both stressed plants (by supplying too much N) and crops with a growth arrest fall prey to fungi. Besides the essantial crop rotation, sprayings with rock meal are also possible. Sprayings with Equisetum arvense extract or pure sulfur are considered effective. At a beginning infestation, we remove the infected plants and burn them. Once the mold has well infected our crops, there really isn't much to do about it anymore without the use of chemical agents.

Bacteria

These microscopicly small organisms can also cause damage to plants (Erwinia and Pseudomona). It are these that cause root rot with tuber and bulb crops and various spot diseases or wilting in other plants. Against bacterial diseases, there are no effective pesticides. Modern varieties are often resistant and a crop rotation prevents damage.

Viruses

Even under a regular microscope, these minuscule organisms are unobservable. In addition, viruses are so primitive that they live can not live outside of their hosts. Yet they are able to cause persistent diseases with symptoms such as growth inhibition and malformations. Viruses can be transferred at dozens of ways such as through aphids, fungi, touching, contaminated irrigation water, ... Viruses are almost impossible to combat. Preventative, one might think of few precautions to help prevent an infection such as:

  • Burning diseased plants
  • Buying healthy seeds/plants
  • Growing varieties that are not susceptible to viruses
  • Carefully combat weeds
  • Effectively combat aphids

Also, we never put young plants or seed beds next to older plants or plants that already bear seeds. Modern varieties are usually resistant to viruses or at least tolerant.

B. Animal parasitic organisms

Nematodes

Nematodes are always present in the soil. The colorless worms are less than 1 mm wide, and are not visible with the naked eye. Most species are decomposers of organic matter, only a few parasite on living plants and sucking their cells empty. The cyst-forming nematodes put their eggs in the soil in cysts (hard spheres filled with eggs, are observable with the naked eye). These cysts can survive years in the soil and awaken when a same vegetable species or a related one is grown. Such a nematode population can cause that a lot or a place fails, seemingly without any reason. We speak of soil fatigue. Infestation by nematodes is promoted by growing a same crop frequently in the same place, this is why we always apply a wide crop rotation. As a defense we can grow Tagetes (marigold). These plants secrete substances through their roots with a nematode-killing property and they are easy to use as a border planting or pre-cultivation.

Insects

Insects belong to the arthropods. Insects have 3 pairs of legs and are usually winged. During their lifetimes, most insects undergo a transformation or a metamorphosis. This can happen through the phase of nymph, where the young larvae already looks similar to the adult insect, but does not have wings yet (aphids, locusts, thrips). With a full metamorphosis the larvae does not yet look similar to the mature insect and a transition first occurs through the pupal stage, often at a hidden place in a self-spun cocoon (moth, beetle). 70% of all known species, are insects, they have a hard skeleton, reproduce quickly and adapt to most environments. Many of these insects have specialized themselves in living on certain crops. With monocultures on large plots this may result in extensive pests. There are some insects that occur on various crops.

Aphids

An aphid is a parasite that appears in the garden from March. They are small(2-3mm),oval, black, gray or green insects, and belong to the order of the lice (Phthiraptera). They carry on their abdomen, two tubular wax glands from which they secrete sugars in the form of a sticky substance which is called honeydew. Ants love it and stay close to aphids. Best known is the green peach aphid and the black bean aphid. Especially in hot weather, the aphids multiply rapidly as they reproduce Parthenocarp and vivipare (without fertilization and viviparous) in the summer. They spawn on the underside of the leaf. Lice are sucking insects that feed on plant saps. We can observe this by the curling and wilting of the leaves and shoots on which they sit (youngest leaves). The damage manifests itself by:

  • Growth inhibition and growth arrest
  • Formation of Dematiaceae, a black fungus on the honeydew
  • Transmission of viruses

Weak or imbalanced plants are first affected. We will thus preventively make sure of

  • A healthy and strong plant (balanced diet and certainly not too much nitrogen)
  • Plant strengthening substances such as nettle manure, seaweed extracts, fertilization with rock flour, sowing of nasturtium catch crops

When infected, we can spray with:

  • A solution of brown soap or an ethanol-soap mixture
  • Organic insecticides such as pyrethrum, or derris, or kwassia (bitter wood)
  • The use of natural enemies such as Coccinellidae, parasitic wasps and Cecidomyiidae in greenhouses

Leaf beetles

These are small (3 mm) beetles with long back legs that can jump high. They are best recognized by their metallic sheen. They eat out holes in the lower leaves of germinating plants. They are especially active in dry, crusty soils with cool and dry weather. One can expel them by pouring cold water over the plants during full sun. To catch them, one can use a glue board. A shelf is foreseen at the bottom with glue or wood tar. In the middle we place soft bristles that are bristled over the crop. The beetles will jump up and get stuck in the glue.

Leatherjackets

This is the larva of the Crane fly, it is around 5 cm long and gray in color. Leatherjackets occur on wet soils overgrown with weeds or where green parts (grass) are dug into the soil. They eat the roots and stems of virtually all crops and can cause major damage. Prevention is done by keeping the ground free of weeds and by not digging grasses under. Leatherjackets can be caught by searching the soil surface on a hot day. We can also use chickens to do this work.

Wireworms

These are copper colored, worm-shaped larvae of the skipjack. They are a typically a problem occuring on newly cleared land. They stay 3 to 5 years under the soilsurface and to grow up to 2 cm large. They mainly eat half decomposed vegetable matter and have a preference for root and tuber crops. They eat the plants roots and drill into the stems, the plants wither from this. Prevention can be done by keeping the soil free of weeds. Wireworms can be caught by cutting a potato in half and digging it in 5 cm deep into the soil with the cut part facing downwards.

Cutworms

This is the larva of a brown moth (Agrotis segetum, Agrotis ipsilon, Agrotis exclamationis). They are about 4 cm large. While resting or in danger they roll up in a spiral. They like warm, dry and light soils where they can hide at daytime. At night they hunt also above the soil and eat young shoots off, precisely at the separation of soil and air. Prevention can be done by already digging in weeds and greens in the winter. Since the larvae are not fond of moisture, the plants can be watered well the first weeks after planting. A good method is a caterpillar bait based on mixing 25% hardwood sawdust, 25% wheat brans, 50% syrup or molasses and water. Caterpillars eat from it, and get stuck in the stuff. In the morning, they are dead. At temperatures above 15°C, we can also work with Bacillus thuringiensis. Administer in the evening, the effect is only visible after a few days. Caterpillars also hate sage, if this herb is planted, they are also expelled.

Spider mites

mites Spider mites are not insects. They belong to the order of the spiders, having 8 feet. The one that does damage to crops is the urticae red spider mite, and mostly spawns under glass. These spider mites suck juice from the plants causing white dots to appear on top of the leaves. Later-on, the entire leaf becomes brown. Spider mites prefer to live in a dry climate. Regular spraying with water makes the threat of infection smaller. Spider mites can also be fought with soapy ethanol. In the greenhouse , we can also use natural enemies such as predatory mites and assassin bugs.

Mammals

Mice and rats All rats and mice do damage to crops. Only the shrew, which is an insect eater, is useful in the garden. Mice can expelled by planting mint. You can catch them with traps or by laying down poisoned bait.

Moles The mole is a useful insect eater, but because of the eating of the useful earthworms and by creating corridors in seed beds, it is an unwanted organism in the garden. They do not gnaw (as sometimes thought) on the plant roots. To fend them off, we can plant crops with a more or less mole-expelling effect such as Fritillaria imperialis (place 1 every 8 meters completely around the garden) and paper spurge (about 10 plants per are), also a clove of garlic in the corridors, would scare off the mole. The most efficient to expell them are mole traps or ultrasound devices.

Rabbits These rodents also do much damage to crops. Near forests, it is best to protect your garden with a dense mesh of 1m high that is also (20 cm deep) dug into the soil. To protect young trees, we can cover them with lime manure. This is made from 3 parts pig manure, 1 part cow manure, and 1 part lime. The whole is mixed well with water, so that a semi-liquid mixture is attained.

Gastropods

The gastropods belongs to the order of the molluscs. They only feel good in wet conditions and are especially active at night. The snails (Gastropods with shell) do not do much damage, only the slugs are voracious. They do not eat, but grate holes in the leaves. Especially the soft parts of plants and young seedlings suffer. Preventive measures are to eliminate the moist places from which they operate, eg by removing weeds, by keeping the grass strips short, by cleaning up waste piles. Wood ash or sharp sand strips of a few cm wide stops gastropods. Gastropods hate some plants such as nasturtiums, sage, hyssop, thyme and mustard. Also, the use of rye as a green manure seems to be expell gastropods. A gastropod trap can be made with a jam pot that we dig into the soil, equal to the soil's edge. We pour in beer up to about 1/3 of the pot; gastropods love it but will drown in it.

C. Non-parasitic causes (physio = disease gene)

Soil Influences

  • Lack or excess nutrients
  • Too much or too little water
  • Poor structure
  • Adverse pH
  • To high salinity

Weather Influences

  • Unaduquate temperature
  • Shortage of light
  • Rain, hail
  • Unaduquate humidity
  • Wind and storm

Air pollution

  • Acid rain

Weeds

Weeds are plants that grow in places where they are not wanted. They can cause damage because:

  • The yield is less due to competition
  • They transmit diseases and pests
  • Because the crop is not ventilated well and there is more chance on a fungal attack

Weeds are wild plants that grow vigorously and will overgrow crops quickly. Weeds are also difficult to get out: seeds spread weeds by the thousands and spread them trough the wind. They can lay for 50 years in the soil, waiting for favorable conditions in order to germinate. In the weed seeds we distinguish between the annual weeds that germinate in the spring and summer (chamomile, ragwort, knapweed) and the biannual weeds that germinate in autumn and form seeds are in the following year (daisy, dandelion). Furthermore, we distinguish the lasting weeds that spread by rhizomes or underground roots, these also being called root weeds (Elytrigia repens, equisetum arvense, thistle, stinging nettle). Stellaria and Poa annua germinates and grows throughout the year.

How to prevent weeds ? Field hygiene: Remove all weeds seeds before coming into the seed formation stage. Weeds on the compost pile are only dead if the temperature in the pile runs high enough (50°-60°C).

Crop rotation: many weeds are linked to certain culture plants. With crop rotation, we shake the weed pattern about. Weed inhibiting plants cover the soil off completely or are spaced so far apart that we can properly hoe between it. Weed promoters do not have these qualities (eg garlic and chive).

Soil covering: The covering of the soil prevents weed growth. With mulching, organic matter is applied in thin layers between the plants. The application of a mulch layer can only happen when the seedlings have grown well above the soil or if the plants are planted. Sowing or planting in a mulch layer is an inefficient task. Do not apply the mulch layer near frost sensitive plants before half May. By covering the soil, it will not be able to radiate heat at cold nights, so the danger of frost damage is then greater.

Cultivation techniques: The needless mixing of soil layers is to be avoided because many weed seeds of the underlying strata are then moved to the soil surface. Sowing in rows facilitates weed control. The planting of firstly nursed plants will give the plants a head start to the weeds. With seedlings, the weeds first need to be left to emerge, these are then hoed, and then the soil is superficially manipulated for the sowing.

Weed control Weeding: this is done in seed beds in which the hoe can not be used. Larger plants are best pulled out. Hoeing and shoveling: this cuts the weeds off just below the soil surface. A shovel scrapes the soil surface, one makes a pushing movement with it as you move back. A hoe is always pulled towards oneself while one moves forward. The best moment is with dry sunny weather after a period of rain, when the soil has dried up sufficiently. The hoeing and shoveling is done when the weeds are as small as possible. The larger the weed, the harder. In dry and sunny weather the weeds can be left to decompose on the soil. In wet weather, the weeds need to be removed from the soil so they can not grow back.

Chemical weed control: Root weeds that simply grow back after hoeing or shoveling due to their underground root parts can be fought with a systemic herbicide that is absorbed in the system of the plant, and which is then transported to all plant parts, including the roots. The more active the plant growth is, the faster and better the effect will be. Glyphosphate is a historic (organicly non-degradable) example. Degradable organic herbicides are now used.

Annual weed seeds can be fought with a total contact herbicide. To prohibit the germination of seeds of annual weeds, soil herbicides can be used, these are sprayed on a weed-free soil and will prevent the germination of weeds.

Weed control or crop protection

Currently, we have come to realize that a trough a set of cultivation measures, the balances in nature need to be maintained as well as possible. This enables to prevent or kill off the development of diseases and pests as much as possible. Within this view, there is only room for limited use of chemical pesticides/herbicides. We call this technique, integrated pest management, in which the use of the use of chemicals pesticides/herbicides is kept to a minimum, and biological control and tillage is maximalised.

A. Preventive cultivation measures

  1. Choosing the right crops according to the specific soil type and the local (Köppen) climate type.
  2. A well thought-out crop rotation
  3. Choosing crop varieties with resistance or a high degree of resistance against diseases and pests.
  4. Proper tillage
  5. Healthy seeds for sowing and healthy nursering of young plants
  6. Favorable sowing and planting times, which takes into account not only the state of the soil, temperature requirements, and correct growing season, but also the magnitude of the risk of damage by parasitic and non-parasitic causes (eg frost), ...
  7. A fertilization oriented to the specific requirements of the plant (non-concentrated nitrogen fertilisation)
  8. Timely and professionally executed cultivation measures (sowing depth, seed spacing, climate in the greenhouse, weed control, ...)

B. Mechanical crop protection

In this, we include all devices and objects that can be used to keep crops healthy.

  • Weeding and hoeing
  • Fences against against damage by wild game
  • Horticultural netting: this is a (usually synthetic) insect net with a very fine mesh (1 mm) trough which no insects can pass

C. Biological crop protection

This involves the use of natural enemies (bred specificly for this purpose) to fight pests and diseases. The natural enemies do this as follows:

  • They suck the plague organism empty , such as the larva of the lacewing and the gall midge and the predatory mite
  • They lay an egg in the plague organism, such as the parasitic wasp.
  • They eat the pest organism, such as the larvae of the ladybug and the predatory bug
  • They secrete toxic compounds into the plague or pest organism to make it ill in one or another way, such as nematodes and bacteria
Pest Natural enemy
aphid parasitic wasp, ladybird, gall midge
Agromyzidae Ichneumonidae
Thrips predatory mite, assassin bug
whitefly parasitic wasp, assassin bug, fungus
spider mite predatory mite, gall midge
caterpillar parasitic wasp, bacteria
Sciaridae predatory mites, nematodes
mealybugs parasitic wasp, predatory beetle
vine weevil nematodes

Source

This article is made using information from the coursebook: Cultivation techniques
Course from: 1st year of Herbalism
Course year: 2005 - 2006
Education center: Syntra, Asse-establisment
Teacher: Leo Van Crombrugge

D. Biologically allowable crop protection methods

Plant extracts: For this, plants are steeped in cold or warm water for a certain period. The liquid is then sifted trough a linen cloth and then sprayed on the crop or on the nearby soil. Most extracts contain trace elements and/or plant hormones that strengthen the cell walls and reinforce the plant's defenses. A number of them also contain substances that kill off or slow down the targeted pest organism. Treatment should thus be often repeated from the start of the cultivation.

  • Wormwood: the poisonous tannins that the plant contains make the crop unpalatable for insects. Effective against aphids and mites. Extract: 200-300 g of dried wormwood is mixed with boiling water. After 1 day, water is added so that 10 liter is obtained. Sift and and spray on the crop.
  • Tansy: animals find the odor and taste of this plant unpleasant and will not eat from it. Usable against various insects. Extract: 300g fresh plant parts per 10 liters of water. Cook briefly first and then allow to rest for 24 hours. Sift and spray.
  • Stinging nettle: the active substance is formic acid. It is the most known, softest cure for aphids, not usable against other insects. Extract: steep 1kg fresh nettles per 10 liter of cold water. Then sift after 24 hours and spray undiluted. Stinging nettle manure: the same mixture is left to stand for about 5 days. Stir regularly and add rock meal. Dilute 10 times and then pour on the soil. The slurry is used as a strengthening fertilizer.
  • Equisetum arvense: This herb contains much silica which strengthens the cell walls. An extract of horsetail has a good efficiency against fungal diseases. Extract: 1 kg of fresh or 150 g of dried horsetail is boiled for 15 minutes in 10 liter water. Let rest for a few hours, sift, and dilute 5 to 10 times before spraying.

Seaweed extract: extracts of brown and blue-green algae contain a high content of trace elements, magnesium and potassium. Their growth-promoting value it attributed to the vitamins, plant hormones and enzymes. It increases resistance to disease and promotes growth.

Derris and kwassia: harmless to humans but it is less effective as an insecticide.

Rock meal: Seaweed calcium, basalt and lava meal have a crop protective function. They increase the acidity which impairs development of bacteria and fungi. The fine rock meals act dehydrating and damage the wax layer of many insects. By dusting or spraying, the plants are covered with a thin layer of dust. Treatment is done in the evening and it should not rain for 12 hours (maximally done for up to 2 times per month). Dosage= 250g/are.

Commercial preparations: Soap: a hot water solution with 1 to 3% (10-30g/liter) soft soap (green or brown) has a moderate working against aphids and some other insects. The insects must be properly hit with the soap solution.

Ethanol-soap mixture: ditto above but add 50 ml of ethanol per liter of water

Sulfur: one sprays pure sulfur against several fungi (mildew and scab). Is harmless to humans and animals.

Bordeaux mixture: is a mixture of copper sulphate and slaked lime. It works preventively to fungal attacks. It is a very old mixture. The copper ions on the leaf prevent the germination of the fungal spores and the calcium also increases the pH.

Pyrethrum: this plant-based insecticide is a strong neurotoxin to all cold-blooded creatures. It is virtually harmless to warm-blooded creatures however. Pyrethrum breaks down within 48 hours. Other plant-based insecticides are Koppert Rotenon and Koppert Plantschoon.

Companion planting Just as it is difficult for people with different opinions to live side by side, plants too have this problem. Plant roots secrete different growth inhibitors and promotors, making a different neighbouring crop grow worse or better. This is called a reciprocal negative or positive influence. The insights obtained from this basic principle was the so-called companion planting. We plant different vegetables, herbs, and green manure crops trough each other or close together, hereby also making sure that the soil surface is covered throughout the year. This method of gardening attains striking results. Except for reasons of pest and disease prevention, there are also other motives, such as more efficient space utilization, higher yields, better utilization of nutrients in the soil, improvement of the flavour of the harvested products, wind sheltering, etc. For those who feel attracted to this, the winter months are particularly suitable for this to attain the necessary knowledge. By reading literature, wikipedia articles or even trough the exchange of knowledge with other gardeners, we can determine the crop combinations for the upcoming season. Whoever starts looking into this, he will soon discover that for crops, there exist good neighbors as well as bad ones.

Crop rotation The aim of crop rotation is to try to reduce the harmful effects of the continuous cultivation of a same crop. Especially in the cultivation of vegetables, we need to change the crops regularly. The yield will then increase. For small gardens, crop rotation seems a pious wish, but where possible, one must still try to use a 1/3 and preferably even a 1/4 system. This means that a given crop can not be replanted on a same spot for three years. This will involve some degree of administration. The benefit of crop rotation in the vegetable garden is that certain parasitic organisms can not build up large infection. Examples are: Plasmodiophora brassicae with cabbage and some soil-dwelling nematodes.

List of possible plant combinations -> To be added

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