4.4 Pest control on farm level

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Preventive measures with regard to storage hygiene are of decisive importance for pest control and in maintaining the quality of the stored produce. By the term storage hygiene, we mean the use of all technical measures without the application of chemicals.

Perfect storage hygiene is the basic prerequisite for successful storage and for the effectiveness of all ongoing measures, such as the use of insecticides. All hygiene measures are very simple, particularly effective and cheap, and can thus be performed by any farmer with little effort.

Figure 21

4.4.1 Traditional Methods

Traditional methods of pest control will certainly continue to play a role in small farm storage in the future. They cause little cost, but their effect is limited, which excludes the possibility of any general application of such measures. Traditional pest control is largely based on the following methods:

• Preventive measures taken before harvesting (see section 4.4.1. I)
• The addition of various substances to the stored produce (see section 4.4.1.2)
• Physical methods (see section 4.4.1.3)

A departure from traditional methods of pest control in favour of modem storage techniques has in the past often led to considerable errors due to insufficient examination of the new methods under practical farmer's conditions. Generally speaking, farmers will accept small, easily-comprehensible and low-cost alterations to their storage methods with the aim of reducing losses. They are, however, for various reasons reluctant to make any radical alterations to the traditional storage systems to which they are accustomed and often correctly so.

4.4.1.1 Preventive Measures Taken before Harvesting

The following methods contribute to preventing pest infestation from the field into the stores:

• Crop rotation and mixed cropping
• Selection of less susceptible cereal varieties (e.g. maize with hard seed coat and husks covering the cob completely)
• Choice of the time of harvesting

Do not harvest too early nor too late!

Watch out for the signs of physiological maturity:

The indicated moisture content at the time of maturity does not mean that the crop is fit for storage. Drying is necessary after the harvest until the moisture content is reduced to values mentioned under section 2.2.5

• Selection of store location (removed from any potential sources of infestation)
• Thorough cleaning repairing of the granary
• Prevention of pest introduction by checking for infestation before storing
• Removal of infested cobs, panicles or pods before storage

4.4.1.2 Addition of Substances to the Stored Produce

4.4.1.2.1 Admixture of Mineral al Substances

There are a variety of different materials which can be added to the stored produce. The three most frequently used types of mineral substances are presented in the following table:

4.4.1.2 2 Admixture of Substances of Plant Origin

Traditionally many different types of plants are used against stored product pests. Although promising results have often been achieved in laboratory tests with plant material (botanicals), the effectivity under practical storage conditions varies a lot. Most methods have a limited effect but some provide satisfactory protection of the stored product when they are applied properly. In the following tables substances are listed which are commonly used and have shown sufficient potential. Methods of application are manifold and techniques which are not mentioned in the respective table may occur locally. Plants which are not listed at all may nevertheless be of local importance and may have a good effect.

Green plant parts and powders made of dried green parts:

Bark and root powders:

Flower, fruit and seed Powders:

Aqueous extracts:

Vegetable oils:

Vegetable oils are added in small quantities to the commodity and mixed thoroughly. They are especially useful for the protection of stored grain legumes against pulse beetles (bruchids). The oils are active against eggs and larvae and disable females to oviposit. The protective effect is generally satisfactory in particular if the grain is still uninfested at the time of treatment.

When plant material is used for the protection of stored products, care should be taken that species with high human toxicity like Datura or Solanum species are not used for cereals destined for human consumption. The same applies to plants which strongly alter the quality of the stored product like some distinctly bitter tasting species. Nevertheless, such substances can be highly useful for the protection of seeds.

4.4.1.2.3 Use of Substances of Animal Origin

The admixture of substances of animal origin does not play any great role in pest control. Cow or goat dung is, however, used for coating the walls of small farm mud silos against hidden pests. The effect is not proven in tests and doubtful. Because of hygienic considerations this kind of treatment should be discouraged.

4.4.1.3 Physical Methods

Physical methods of pest control are applied both preventively and curatively. Processing may contribute to an increase in storability. Refer to section 10.1 for further details.

4.4.1.3.1 Mechanical Methods

• Removal of pests, infested grain or cobs by hand
• Sieving
• Winnowing
• Moving the grain (shaking, restacking)

When using methods which merely separate the pests from the stored produce and do not result in their death (e.g. sieving), care should be taken to ensure that the pests removed from the produce are killed to prevent reinfestation.

4.4.1.3.2 The Use of Heat

• Spreading out the produce in the sun (larvae living in the grains will be killed, the adult insects which are sensitive to heat and light will flee).

Avoid overheating!

• Heating in water (parboiling)
• Smoking or burning out storage containers (e.g. mud silos)
• Storage of grain above the kitchen fire (heat and smoke will chase the pests)
• Smoking with dried hot pepper (Capsicum sp.) has a very good immediate effect, but changes the taste of the grain.

4.4.1.3.3 Airtight Storage

Scaled storage is ideally suited to control insect and mite infestation in dry grain without the use of pesticides. I he principle of the method is namely the elimination of the oxygen that insects and moulds require for their growth as well as an increase of the CO2 level (see section 4.1.2). This is due to the respiration of the pests and grain. In this context the importance of a good, sound construction or container cannot be overstressed. Good thermal insulation is essential.

Airtight storage is particularly applicable for long-term storage in warm dry areas. It might be advisable, however, not to store seed grain for more than a few months under these conditions.

In tropical countries, where the relative humidity is at the optimum for mould growth, airtight storage is generally not recommended. Potential dangers with this storage method can be reduced by careful management, by storing well dried commodities only and particularly by ensuring a more or less even temperature in the store which exclude the risk of condensation.

4.4.2 Biological and integrated Means of Pest Control

Biological and integrated means of pest control are dealt with in greater detail in chapter 10. The use of natural enemies (predators, parasites), of specific micro-organisms, as well as food traps and varieties more tolerant to storage pests will grow in importance in small farm storage in the future.

With regard to biological control of stored product pests first experience with the release of an antagonist of the Larger Grain Borer (Prostephanus truncatus) have shown promising results in storage on farmers level (cf section 10.3).

Another approach of integrated stored product management for small-scale farmers is based on dividing the harvest with the aim of reducing the quantities of insecticide necessary for adequate prevention of post-harvest losses. Tests carried out in Tanzania as well as surveys in West Africa have shown that during the first three to four months of storage pest insects generally do not produce economic losses which justify treatments with synthetic insecticides.

Considering this fact it has been concluded that the harvest can be divided in one part destined to consumption in the first three to four months after harvest and another part intended for storage over a longer period. The first part can be stored without chemical treatment, whereas cereals determined for later consumption or for sale are to be treated. This procedure allows the farmer to save insecticide and money without negative economic consequences.

4.4.3 Chemical Methods

For centuries, farmers have relied on the protective effects of husks or pods and have selected traditional varieties with a low susceptibility to storage pests. 1 his confidence is by all means justified. Therefore any interference in the farm storage system in order to avoid the drawbacks of traditional methods by an increased use of insecticides must be carefully examined with regard to social and economical effects.

As the traditional means of pest control do not seem adequate to protect the increasing stored quantities all over the world, efforts are being made to introduce changes to traditional storage systems. These efforts are generally centred around the use of insecticidal dusts which are mixed with the produce. The introduction of chemical stored product insecticides on farm level, however, has caused a number of problems which could not be satisfactorily solved in spire of the considerable efforts made by the respective extension services.

Surveys done in West Africa in recent years have shown, for instance, that inadequate choice and application of chemical insecticides and fumigants on farm level is very common. In the investigated cases it resulted, that correct application is only practised by a minority of the farmers. The following mistakes are particularly widespread:

- choice of an inadequate product

Among the chemicals used by farmers for the protection of stored food grain frequently products for seed and soil treatment or insecticides against hygiene pests like mosquitoes or cockroaches have been indicated. Some of these products contain active ingredients with high mammalian toxicity in high concentrations. The health hazards of these practises for the consumers are evident.

Obsolete compounds like chlorinated hydrocarbons are still applied in Africa for purposes like control of mosquito larvae and end up rather often as grain protectants in food granaries.

- application of degraded or inadequately formulated insecticides

In many cases where farmers complained about the insufficient effect of recommended stored product insecticides, chemical analysis has shown that the active ingredient had degraded due to overstorage or storage under unfavourable climatic conditions. Especially dustable powder formulations degrade rapidly under hot and humid climatic conditions.

In some circumstances, however, it could be proven that errors of formulation from the local factory was the cause of the failure. There have been cases where the content in active ingredient was zero from the day of production.

- inadequate application

Errors in dosage calculation or uneven distribution occur frequently and result either in overdosage with the respective risks for the consumer or in underdosage. Underdosage means insufficient stored product protection and the promotion of development of insecticide resistance in storage pests.

Fumigants are readily available in many rural West African markets. Dealers sell even single tablets wrapped in paper. Surveys have proven that whenever fumigants are applied by small-scale farmers in Africa the conditions for gas tightness are not fulfilled. This means that the treatment does not have the desired effect and there is a considerable risk of human intoxication.

The reason of the above listed problems is mainly the inadequate information of the farmers. Dealers selling products are not well informed to advise the farmer on the correct application or they are not interested in discouraging farmers to buy an unsuitable product. Labelling is frequently not sufficient to prevent misuse, especially as there arc rarely labels in local languages. The high proportion of illiterate farmers poses additional problems concerning the transfer of special technical informations. And last, but not least, many extension or plant protection services are not in the to provide the necessary knowledge where and when it is needed.

Unless an efficient extension / information system on correct insecticide application particularly for African farmers is installed, the best solution seems to be the reduction of insecticide use for post-harvest protection purposes to the absolute minimum. Hygiene including all kind of preventive measures has proven to be the most effective, the most economic and the safest approach to post-harvest loss prevention on farm level. Some of the traditional methods based on substances of plant origin, minerals, etc. show sufficient action on stored product pests to compete with synthetic insecticides, in particular if such products are applied by farmers without the necessary skills (see section 4.4.1).

In most African countries dustable powders are the most widespread formulations for stored product protection on farmers' level. This is due to the fact that the application of dusts is comparatively easy and safe, although spray applications may be more effective under certain conditions. Therefore this section deals exclusively with the application of dust formulations on farmer's level. More detailed information on the possibilities and limitations in the use of chemical insecticides, the choice of suitable insecticides, safety aspects and others is provided in chapter 8.

The following points must be taken into account when using chemical means of pest control:

• Toxicity of the insecticide / user protection (see section 8. 1.7).
• Economic viability of an insecticide treatment. Experience has shown that the treatment of cobs of maize in husks is not always economically viable, particularly in cases when the maize has already been heavily infested in the field. This also applies to the treatment of stored produce which does not remain in the farmer's storage container for longer than 3 to 4 months (see section 4.4.2).
• Availability of the correct insecticide at the right time and in the right place
• Suitable, i.e. small package sizes with labels bearing instructions for correct use (in common or in local language)
• Farmers' knowledge in dealing with insecticides based on appropriate extension measures

Therefore chemical insecticides can only be propagated when these facts are assured and a functional supply system and competent extension service is available.

There are two areas of insecticide application in small farm storage:

• Space treatment of stores (dusting, spraying, smoking) provides good preventive pest control.
• Treatment of the stored produce with insecticide dust either by mixing it with the stored produce or applying it in layers as well as treatment by spraying or by smoking.

Attention: in order to avoid residues above the admitted level (see section 8.1.8), the admixture of an insecticide to stored product can be done only once per season even after a prolonged period of storage.

4.4.3.1 Dusting

4.4 3.1.1 Dust Formulations

Dust formulations of insecticides are sold ready for use and contain 0.1 to 5% active ingredient. The formulations contain additives which increase the adhesion to the stored produce. Dust formulations are suitable for mixing with grain and for applying in layers in the stored produce (sandwich method) as well as for surface treatment of individual bags, bag stacks and stores. The most common insecticides at present in use are:

Information on the correct choice of active ingredients and on the properties of the listed products is provided in section 8.1.6.

4 4.3.1.2 Dusters

Dust formulations are applied by means of a duster. There are very cheap and effective models which can easily be made locally or are available on the market:

4.4 3.1.3 Application of lnsecticide Dust: Admixture with Grain

This method applies in storage of small quantities of loose grains. The dust is mixed with the grains as follows:

Figure 22

Figure 23

Figure 24

Figure 25

1. Pour the grain in a heap on the floor
2. Evenly distribute the required amount of insecticide on the heap
3. Carefully mix together insecticide and grain using a shovel
4. Check that the powder is evenly distributed

Figure 26

Figure 27

Figure 28

Figure 29

Bag and store the treated grain or place it in a suitable container.

With larger amounts of grain (more than two bags) it is advisable to mix the dust with the entire heap by reshovelling it a number of times

4.4.3.1.4 Application of Insecticide Dust: Sandwich Method

The sandwich method is suitable both in the storage of maize cobs as well as for other cereals. The stores must be thoroughly cleaned before storing.

Storage and the application of insecticide may then commence:

Figure 30

Figure 31

Figure 32

1. Sprinkle the inside walls and floor with a fine layer of insecticide
2. Put in a layer of maize cobs (no thicker than 20 cm)
3. Sprinkle dust evenly over the layer of cob
4. Put in more layers of cobs and dust each layer

Figure 33

Figure 34

Figure 35

Figure 36

5. Finally dust the top layer thoroughly:

The degree of field infestation of maize depends largely on the close cover of cobs provided by the husks. Studies have shown that storage of cobs fully protected by the husks can be as effective in preventing losses as a treatment with insecticide. Removing the husks before applying any insecticide can, however, be of considerable advantage in cases of previous field infestation as insects already inside the cobs will then come in contact with the insecticide.

4.4.3.1.5 Dosage Calculations for the Application of Dust Formulations

Application rates for dust formulations are given either in g commercial product per 100 kg of grain or in ppm (parts per million). The indication ppm refers to the amount of active ingredient (a i.) in the grain.

Figure 37

A value of 10 ppm means there are 10 weight parts active ingredient contained in 1 million weight parts of the stored produce. As 1 kilogram contains 1 million milligrams, 10 ppm means 10 tug of a.i. per kg of grain.

Determination of the quantities of insecticide Just required for the treatment:

- Application rate given in g/100 kg

Informations required for the calculation:

• Weight of the produce to be treated (in kg)
• Recommended application rate (in g/100 kg)

The amount of stored produce to be treated (in kg) is multiplied by the application rate (indicated in g/100 kg).

Example: 500 kg of maize are to be treated.

The recommended application rate is: 50g/100 kg

Calculation: 50g / 100 kg × 500 kg = 250 g

250 g of the dust formulation are thus required to treat 500 kg of maize.

- Application rate given in ppm

Informations required for the calculation:

• Weight of the produce to be treated (in kg)
• Active ingredient content of insecticide (in %)
• Recommended application rate (in ppm)

The calculation of dosage is performed in four steps with the aid of the ppm table at the end of this section:

• The top row in the table lists various recommended application rates in ppm. Find the column referring to the given application rate of the insecticide being used!
• The column on the left in the table lists various active ingredient concentrations in %. Find the row applicable for the insecticide being used!
• Find the point where the applicable row and column cross! The figure stated there is the amount of the dust formulation (commercial product) in g which is necessary for the treatment of 100 kg of stored produce.
• Calculate the required amount of dust formulation for the actual amount of produce being treated.

Example: 300 kg of grain are to be treated.

The selected insecticide is a 5% dust formulation.

The recommended application rate is 10 ppm.

The point where the 5% row crosses the 10 ppm column shows the required amount of the insecticide for 100 kg of grain: 20 g.

This figure is converted for 300 kg of produce:

20g / 100 kg × 300kg= 60g

60 g of the 5% dust formulation are thus required to treat 300 kg of grain.

- Dosage calculation for the sandwich method

In the sandwich method, the same dosage is applied as for an admixture of insecticide with the stored produce. The total amount is thus calculated on the basis of the quantity of stored produce in kg as described above.

For each layer with a maximum thickness of 20 cm the corresponding amount of insecticide is calculated according to its weight. Care must be taken to have layers of the same thickness.

It is recommended to retain a part of the calculated quantity of insecticide to treat the floor, walls and the top of the storage container during filling. When storing the produce on platforms, retain a part of the insecticide from each layer to dust the outside of the stack once al I the produce has been put into storage.

Example: Maize cobs are to be treated using a dust formulation.

The recommended application rate is 50 g/100 kg.

2 baskets of maize cobs make up one layer. The average weight of the baskets is 60 kg. The overall weight of the first layer is thus:

2 × 60kg= 120 kg.

50 g / 100 kg × 120kg = 60g

of the dust formulation must be used for the treatment of the first layer including floor and part of the wall.

2 baskets of maize cobs and 60 g of insecticide should also be used for each subsequent layer including the final coverage.

There are sometimes difficulties for farmers in calculating the weight of produce being treated. It is best to weigh the produce before storage or count the number of bags or baskets emptied in the store. The average weight of one bag or basket must then, however, be determined.

Table for the calculation of the amount of dust needed to in treat 100 kg of grain

Example:
a) You have to treat 2 t of grain with a dust containing 2% a.i
b) The recommended application rate is 10 ppm.
c) How much dust is required for the treatment?
d) 1 hid the intersection of the 2%-line with the 10 ppm-column!
e) Calculate the amount of required for 2 t (= 2000kg): (50g/100g) x 2000 kg = 1000 g = 1 kg
f) 1 kg of a 2%-dust is required to treat 2 tons of grain at the application rate of 10 ppm.

4.4.3 2 Application of Liquid Formulations

Should liquid formulations be used in small scale farm storage, please refer for application instructions and calculations of dosage to chapter 8.

4.4.3.3 Fumigation

In many areas in Africa, Asia and South America, grain is stored in sealed containers made out of mud. Some years ago fumigation of these stores seemed to be a highly promising method of pest control even on small farm level, particularly as this technique is simple, cheap and effective (when applied by well-trained personnel!) and does not leave any residue in the stored produce.

Lack of control and risks to users and people not involved in fumigation have, however, repeatedly occurred as a result of incorrect handling of fumigants by untrained farmers. As a consequence of poor sealing the desired effect has rarely been achieved. Instead men and animals are exposed to severe health hazards. Therefore fumigation on small farm level must be entirely discouraged.

4.4.4 Control of Termites

In traditional granaries or smaller warehouses made of mud termites can appear as a considerable nuisance. Often they do not cause substantial damage to the stored products, but they destroy storage structures, especially wooden parts of the construction or straw.

Termite control is rather difficult to achieve. l he best approach is prevention, as it is the case with other stored product pests, too. Several hard wood species like, for example, teak resist to termite attack. In zones where termites are frequent mud constructions without straw perform better. Poles of granaries soaked with mineral oil at the bottom end may resist during several years. There are also insecticide formulations available developed for wood protection (e.g. deltamethrin), but very often it is difficult to obtain them in rural areas of Africa. Solid constructions providing barriers against the intrusion of termites are to be recommended in exposed zones, but it must be taken into account that termites are quite successful in finding minor fissures which provide access, so that regular inspection, destruction of galleries and immediate repair of damage to storage structures is necessary under all circumstances.

Some of the plants used for traditional stored product protection are said to have termite-deterring effects. One of these plants is Hyptis spicigera (cf. 4.4.1.2.2). However, these effects are not yet well studied.

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