Farmers continually battle insects and diseases that attack their crops. Also they struggle with weeds growing in the midst of the crops and competing with the crop for vital nutrients, air, water and space. When used correctly and with care, pesticides are helpful in improving the quality and dependability of food supplies. Some pesticides have however shown detrimental effects on the environment and human health. In addition, some pest species have developed resistance against these once effective pesticides. Because of this, farmers have turned to integrated programmes of pest management. These controlling programmes involve the use of pesticide sprays, biological control measures, mechanical control, trapping methods and agricultural methods. The use of other alternatives such as intercropping and moving away from monoculture (continuous growing of a single crop on the same fields or growing the same crop over an extended area) toward the rotation of crops during a set period of time is also included. This has aided in improving pest management in the crops. Some rotational programmes may be somewhat limiting due to different soil types, climatic conditions and financial limitations. Monitoring crops for the presence of pests is an integral and important aspect of integrated pest management.

Insect control practices Insect control methods include chemical control and non-chemical control. Integrated control is achieved when chemical and non-chemical control methods are integrated in a programme. Non-chemical pest control includes physical control, agricultural control, natural control as well as biological control. Insect control practices are detailed below: Natural control Natural control is concentrated around the environmental factor which prevents increases in pest numbers and their spreading. It also includes the presence of natural pest enemies in the environment. Physical control Pests can be controlled by making use of physical or mechanical actions, meaning that physical changes are made in the environment. Physical control methods include:

o Physical removal of the pest, disease or weed a crop situation by hand, which is impossible in

o Mechanical execution of the pest making use of fly screens on windows

o Mechanical traps i.e. those that are non toxic, such as sticky traps and electric traps

o Manipulation of the environment has limited application, but can be used with success in processes such as dehydration, low relative humidity and regulating temperature.

o Control through agricultural practices

o Pest control through agricultural practices is used in the large-scale cultivation of crops. It is relatively cheap and environmentally friendly.

Such practices include:

o Ploughing in of host plants for pests

o Sanitation practices

o Destroying remnants of pest infested crops

o Crop rotation

o Mixed cultivation

o Strip cropping

o Establishment of trap crops

o Cultivation of pest resistant crops

Biological control

Biological control is the manipulation of pest’s enemies (parasites, predators and pathogens) in such a way that pest numbers are reduced. Biological control agents for pests are specific to a pest species and once established can increase and spread independently making the control self perpetuating. The control is however expensive, slow and the pest cannot be eliminated even for short periods of time.

Genetic manipulation

The Sterile insect technique, also called Genetic manipulation, is a form of biological control where numerous sterile male insects are released into an area where these insects are problematic. The sterile males will mate with females but nothing will come of? it, meaning that she can not add to the population. The release of sterile males into a normal population has shown to be effective in parasitic fly pests in Central America. This process however is very expensive. By manipulating the genetics of crop plants can produce pest resident crops. The plant will either repel the pest or produce toxic compounds. An alternative is a crop plant where growth is stimulated through insect attack, the crop thus compensates for the losses due to the pest. An example of this is found in cotton and soybean plants.

Chemical pest control

Chemical pest control is done by using pesticides. The term pesticides refer to the wide spectrum of agrochemicals used in plant protection. Pesticides include herbicides (plant or weed killers), insecticides, fungicides (killing fungi), bactericides

(killing bacteria), rodenticides (rodent killers), avicides (bird killers), molluscicides (snail killers) and acaracides (mite killers). Insecticides are classified in three major groups according to their mode of action; the contact insecticides, systemic insecticides and those with stomach action. Contact insecticides enter the insect primarily through the exoskeleton and do not penetrate the leaves and are not translocated through the plant, whereas systemic insecticides must be taken in during feeding. The compounds are taken up by the plant and translocated throughout the plant. Insects with sucking feeding habits are the primary targets of systemic compounds. Stomach poisons must be ingested and is absorbed in the stomach of the insect. Fumigants, pesticides in a gaseous form, enter the insect through the respiratory system. Pesticides with trans-laminar action penetrate the leaves of plants, but are not translocated through the plant. Insecticides are classified according to their chemical structure. There are four major groups of compound that can be distinguished: The organo-chlorines insecticides, primarily contact or stomach poisons that effect the nervous system through disruption of impulse conduction. The best known pesticide in this group is DDT. The organophosphate insecticides are also nerve impulse disrupters. The majority of these compounds are contact killers, but some organophosphate act as stomach poisons and systemic compounds. The carbamates have the same mode of action as the organophosphates. The active ingredient carbaryl and aldicarb fall in this group. The synthetic pyrethroid insecticides were developed from the natural insecticide found in plants, pyrethrum. These compounds are highly concentrated and are thus applied at very low dosage rates. Pyrethroids have both a stomach and contact action but are not systemic.

Mating disruption

Mating disruption occurs when pheromones are released (normally full cover spray or selected releases), disturbing the males in a way that they cannot locate the females. In this way mating is interrupted.

Monitoring crop fields for pests, diseases, weeds and benefits

Why pests should be monitored.

In order to prevent crop damage from insects and diseases it is essential that crops are inspected regularly. These inspections could be done in conjunction with inspections for weed densities, diseases and crop nutrient and water status. Crop monitoring indicates the pest’s and disease status of the crop. In this way the crop producer remains informed of the health status of his crop. Information on the crop disease and pest status enables the farmer to make decisions on whether control actions need to be taken and to select a suitable control action when necessary. The farmer can now apply a once-off chemical crop treatment instead of sticking to a strict spraying programme. In this way the amount of pesticide applied and labour inputs can be reduced, thus reducing crop production costs. Some kinds of insecticides and fungicides/bactericides can even be mixed during the same spray action.

Pest to beneficial ratios

Pests attack crops because it is a food source to them. Under balanced conditions, the pest population will likely be balanced by a population of other predator insects or animals. As the predator population decreases, the pest population increases, as well as the extent of crop damage. Pesticide treatments will have to be applied in such cases. In a balanced system the natural predators will pressurise the pest populations, thus preventing pesticide treatment.

Scouting for crop pests, diseases and weeds

The monitoring process is generally known as scouting. Scouting is used to identify pest species present as well as the extent of pest infestation. This can also be applied to crop diseases. In the case of crop diseases it is not always possible to identify or see the actual agent of disease. Thus when monitoring for crop diseases the scouting process is aimed at identifying symptoms of disease rather than collecting, identifying and counting individual pests. Plant samples can be collected for identification by experts. A pest control programme is based on the infestation threshold as well as economic thresholds for pest control. The programmes take into account the growth stages of the crop plant and relate this to pest infestation rates. This aids in evaluating the vulnerability of the crop and the potential for damage that exists. The occurrence of natural pest enemies and pathogens must also be taken into account in the monitoring process.

The monitoring process starts with surveys. Monitoring techniques exist to aid in crop survey. The two most useful survey techniques are; the step-wise and transect method of scouting or placement of traps. Both techniques require the investigator to walk through a field, then stopping and sampling or scouting or counting at pre determined, set intervals. Where scouting is done for diseases the monitor should collect leaf, shoot, bud and fruit samples for identification by experts. Where the presence of diseases is suspected, samples must be collected and sent for analysis and identification by an expert. The transect-scouting method involves scouting along a line across a field. The line can be diagonally across the field or parallel to the side of the field. A minimum of five sampling points per hectare should be selected. When using the stepwise scouting method the scout starts in the middle of one side of the field. The scout then moves forward and to his right stopping at pre determined distances. Once he has crossed the whole field, the scout moves to the point of origin and repeats the exercise, but now moving forward and to his left. A maximum distance of 5 m should be used as a pre set distance. Once samples of insects or diseased plant parts have been collected, the insects and diseases are identified. Counts of the number of pests are done to determine the infestation rates. Based on the identity of the pest and degree of infestations, crop information and environmental information, a management strategy can be implemented. At the pre-determined intervals, using either of the scouting methods, sampling techniques for insect collection can be used.

Sampling techniques generally used in pest monitoring are set out below:

• Shake and beat method: involves placing plastic sheeting underneath the crop plants and by shaking or beating the plants with a stick will cause insects to fall on the sheeting and which are then collected and counted.

• Knock- down sampling: an insecticide is applied to a small area within the target area which will kill all insects present. Similarly to the shake and beat method, insects are collected on a pre-set plastic sheet.

• Baits containing insecticides: can be used to attract and sample insects, e.g. laced molasses.

• Mites can be sampled by brushing the crop leaves onto a glass sheet. Alternatively mites can be brushed onto a flattened paper and the stains on the paper counted.

• Sweeping nets are used to collect flying insects, such as leaf-miners. The net, made from suitable material, is swept across the plants and collecting insects.

• Malaise traps are used for active insects and consists of a net with one open end (tent like). A container for trapping the insects is placed at the highest end.

• Sticky traps are made from a suitable surface with a sticky coating. The sticky trap can be baited to attract certain species. The trapping efficiency of these types of traps is influenced by environmental conditions and the positioning of the trap.

• Water traps are suitable containers containing water to which a soapy substance and a preservative is added, erected 1 m above soil level. The traps are suitable especially for trapping aphids.

• Sucking traps are basically modified vacuum apparatus which sucks the insects into a net.

• A light trap is a lamp, usually ultraviolet, surrounded by a vertical baffle; at the top of a funnel–shaped container and a sampling container at the bottom.

• Pheromone traps are used for moths and butterflies. Pheromones (sexual hormones) of the targeted species are placed in a suitable container. The traps are set up over a large area and are suitable for monitoring the population increase and also for pesticide application timing. Pheromones are odours produced by an animal that affects the behaviour of other animals.

• Pheromones work in a similar way as hormones in that they send specific chemical signals from one set of cells to another. Once these signals reaching the target site, a reaction takes place. In insect pest management this characteristic is often used to attract a pest to a specific area. The pheromone is placed into a trap which attracts the insect. The insects will enter the trap but can then not escape. In some cases a decoy is used which will attract the insect. The traps are useful in determining the number of insects that are present in the vicinity of a crop field.

• Determining the rate at which insects are moving into a field helps to estimate the potential damage that they could do. This in turn is used to decide how the pest can be controlled.

• Pheromone traps are usually made of plastics nets which are then placed in a field, containing a small container in which the bait (pheromone) is poured. Insect pheromones are very specific and will only attract specific species, thus helping in the identification of the target insect. Pheromones are chemicals excreted by the female that attract male moths. Therefore, only male moths are caught in these traps. The chemicals usually have a short lifespan and must therefore be replaced at regular intervals. The insects caught in the traps need to be removed and counted allowing the next count can be made. This data is called temporal data of insect population.

• Pit fall traps are containers with a small volume of preservative which are placed into the soil so that the open end is level with the soil surface. These traps are effective for insects that live on the soil surface.

• Soil sampling for soil dwelling insects can be done by using and auger-like soil coring device or a blade sampler. It is important that the volume of soil is known ensuring that the calculating of the infestation is done per volume.

• Spore traps. Some fungi like powdery mildew produce airborne spores that can be sampled using special spore traps

Record keeping

Monitoring goes hand-in-hand with record-keeping. Monitoring create the “farm memory” as it is, with reference to beneficial insects, pests, diseases and weeds that are present on the farm and on specific fields. The records should provide information regarding when and where pest problems have occurred, information on the cultural practices applied (irrigation, cultivation, fertilisation etc.) and their effect on pest and beneficial populations. The records should also include information on the pest management practices that have been applied. Where possible, the effects of aspects such as weather, on pest and beneficial populations, should be recorded. During monitoring, all data collected must be recorded. It is important to know the density of occurrence of pests, diseases and weeds. Also one has to know where these occurred and when these were first observed. All data must be written down and kept, not only for a particular season, but kept for a number of years, allowing the farmer to trace trends and timing of various problems. Not only should you keep record of the problem, but also of the treatments and interventions made to control the problem. This allows one to track what has been tried and how successful these have been.