AgriGuide

Pest and Disease Management

Pest and Disease Management

Prevention of damage, promoting natural enemies

The natural enemies of crop-damaging insects and mites are also farmers’ allies. There are two groups of natural enemies: predators and parasites. Predators eat their prey. The most important predators are harmless to crops and people.

Well-known predators include spiders, predatory mites, lady beetles, ground beetles and hoverflies. The advantage of these predators is that they multiply just as rapidly as their prey. The most common parasites are wasps and flies. They lay eggs in the pest insect’s larvae, and then their larvae eat the host from the inside out. Predators eat many different species of insects or mites, but parasites are often specialized in one type of pest insect. As adults, their diet consists entirely of pollen and nectar, often of wild flowers. If there is a sufficient number of natural enemies present at the start of the growing season, they will normally keep the pest insects and mites under an acceptable level, so crops can remain healthy.

The farmers can also take measures to help the natural enemies out a bit. Diverse vegetation around pieces of land offers shelter where they can survive between growing periods. Farmers can stimulate their growth even more by sowing flowering herbs around and in the fields where crops are grown. Farmers can also build additional housing for predator insects or parasites.

Preventing the spread of pests
Vegetation in and around crops does more than just supply shelter for natural enemies. High vegetation around fields keeps flying insects away, as well as mites transported by the wind. A second crop in a field can also serve as a physical barrier, in addition to the advantages mentioned. Rows of specific crops can deter or attract pest insects with their smell: these are known as repellent crops and trap crops.

Crop rotation
In crop rotation, farmers can alternate crops that are eaten by a certain pest with crops that are not eaten by that pest. Crop rotation is part of a multi-annual strategy to minimize the number of pest insects on a farm.

Short growing season
If farmers are mainly growing one crop, and crop rotation is not a viable option, it is especially important to extend the period between crops as long as possible. The number of pest insects will decrease during the crop-free period. Farmers can also enhance this decline by working the plant residues containing the pest insects deep into the soil, or by bringing the pests to the surface where they are vulnerable to attacks from their natural enemies. It is recommended to keep the growing season short by sowing or planting over as short of a period as possible. The same is true for harvesting. It may also be better not to wait until the last plant can be harvested or the last fruit is ripe, because the longer you wait to harvest, the more surviving pest insects there will be when you plant the next crop.

Removing crop residues
If there are many pest insects left after harvesting, it is better to remove the crop residues together with the pest insect than to leave the residue in the field. However, if there are relatively few pest insects present on the crop residues and many natural enemies, it may be useful to leave the crop residue in the field.

Fertilizing
It is important to fertilize in a balanced way, with enough P and K and not too much N. Too much N makes the crop appetizing for insects, and leads to a dense crop, in which it is more difficult for pest insects’ natural enemies to find them.

Control
Even with all the preventive measures mentioned above, the number of pest insects could become too high and threaten to cause unacceptable damage to the crops. It is important to inspect the crops every week in order to determine whether critical levels are being reached.

Information on critical levels (such as the number of pests per sqm or per meter of a row) should be available for the field. As soon as the number of pest organisms is too high, farmers can consider taking corrective action.

Catching by hand
If pests’ population is not large, relatively big insects can be caught by hand and squashed.

Catching in traps
It is less labor intensive and less tedious to control these pests by luring them into traps. The most common types of traps give off light to attract night insects, are made of yellow strips covered with glue, or contain some kind of bait.

Biological control with beneficial insects and micro-organisms
If it appears that the natural enemies of the pest insects and mites are staying in the margins of the field rather than moving into the center, farmers can carry them by hand into the field. Sometimes natural enemies that are bred elsewhere are offered for sale. These can be predators or parasites, but also nematodes or disease- causing fungi, bacteria or viruses.

Nematodes are primarily used to combat soil insects. Viruses, bacteria and fungi are sprayed over the entire crop and work against the pest insects that are present on the plants.

Control using plant extracts
Many plant species, both cultivated and wild, contain substances that can kill insects. You can easily make a spraying liquid out of these plants yourself. Plant extracts have both advantages and disadvantages compared to chemical pesticides. The most important advantages are:

  • Less expensive; and
  • Decompose faster, so no residue is left on the crop.

On the other hand, the main disadvantages of plant extracts are:

  • That they often have a weaker effect than synthetic insecticides. Many insects survive or just become ill and then recover;
  • The required dosage differs according to the insect species. As farmers manufacture the spray themselves, they will have to determine the optimal dosage through experimentation;
  • Some extracts (such as tobacco juice that contains nicotine) are poisonous to humans and pets. Just as with chemical pesticides, farmers have to handle these extracts with care;
  • Most plant extracts are toxic to natural predators or parasites of pest insects, so the ‘natural balance’ will be disturbed when using these bio-insecticides.

Farmers in Cameroon select plant extracts with insecticidal properties

Various non-chemical crop protection methods and products have been tested under local conditions in Cameroon.

First, an inventory of traditional methods of pest control was conducted with small-scale farmers in the North-West, South-West and West provinces of Cameroon. Information was gathered from their answers and from literature, and a booklet was prepared for distribution. Farmers were trained in non-chemical crop protection methods for controlling pests on their farms. The training methodology was based on a participatory approach and Farmer Field School.

One of the promising preparations subjected to field-testing after this inventory was castor oil (Ricinus communis).

The preparation is as follows: 0.5kg shelled or 0.75kg fresh unshelled seeds are mashed and then heated for 10 minutes in 2 liters of water. 2 teaspoons of kerosene and a bit of soap are added. The solution is sifted (through a cloth) and diluted with 10 liters of cold water. The preparation is then ready for application on the leaves, to control leaf-eating caterpillars, aphids and true bugs on vegetable crops. Castor oil is poisonous for humans as well as for the natural enemies of pests.

Extracts from the Neem tree (Azadirachta indica) are also widely used. Neem extracts have an effect on nearly 400 species of insects, including major pests (moths, weevils, beetles and leaf miners). They do not kill insects directly, but effectively prevent their reproduction. Neem extracts can be prepared from leaves, but the seeds contain higher concentrations of insecticidal components. 75g of seeds (including the seed coat) should be used per liter of water.

The seeds should be at least between 3 and 8-10 months old. The pounded kernel powder is gathered in a muslin pouch and soaked overnight in water. The pouch is squeezed and the extract is filtered. Some soap is added to the filtrate (1 ml/lt of water) to help the extract stick to the leaf surface of crop plants.

Papaya leaves can also be used: 1kg of fresh leaves, shred and soaked in 10 liters of water, add 2 teaspoons of kerosene and a bit of soap, and leave it overnight. Sift the decoction through a cloth, and the spray is ready for application on the leaves of vegetables, against leaf-eating caterpillars, aphids and true bugs.


Is one able to buy neem pesticide directly (in Europe, Africa, etc.), or does one have to make it at home?

A Neem (Azadirachta indica) oil pesticide is a natural way to control pest and diseases affecting crops as well as plants or flowers. Neem oil has been used for hundreds of years due to its ability to repel bugs. African farmers are using neem as an organic alternative to toxic chemicals that pollute the soil, water supply, along with harming children, birds and good insects.

African farmers Most Neem Oil is good quality but check the label to see what has been added to it as some have been diluted more than others. You can find it in most health stores as Neem Oil or Neem Leaf extract and it should be organic.

Neem can be easily made at household level by following the instructions as:

  • Container big enough to hold two quarts of warm water to mix it in.
  • Add ½ teaspoon of a mild liquid soap like Castile and mix it up, and then add ½ ounce of Neem Oil slowly into the water while stirring it or slightly shaking it up.
  • Now pour some into an old, clean spray bottle of some type or into a new one.
  • You can double this recipe but it should be used within 8 hours or it will lose its potency.

Spray all of the leaves wholly with your homemade pesticide on the top and bottom and saturate the soil with it, too. Always spray early in the morning or early in the evening to avoid scaring off the good bugs and scorching the plant in the hot sun.

Make sure to shake it while spraying to keep it well mixed, and repeat the spraying once a week and more if it rains.

It will not instantly kill the insects until they bite into the leaf, but it will instantly repel them with its strong smell.

Neem Oil pesticide has been known to kill and control aphids, moth larvae, spider mites, whiteflies, and Japanese beetles. It will not harm insects that do not chew the leaves like butterflies, ladybugs and bees.

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