Monitoring Methods

To prevent crop damage from insects and diseases it is essential that crops be inspected regularly. These inspections should be done regularly and could be done in conjunction with inspections for weed densities and crop nutrient and water status.

It is important to observe a growing crop closely. Insect and disease damage can occur literally overnight. Farmers must be aware of the condition of the crop always. Crop rows may be hundreds of metres long or consist of thousands of individual plants; therefore, one cannot monitor all the plants all the time. It is thus wise that the farmer select several control plants or groups of plants that represent the condition of the plants on a crop field. These plants should be marked and individually numbered, enabling them to be repeatedly visited and their conditions checked. This process is known as monitoring.

The plants are monitored on a regular basis for the following reasons:

• Leaf condition (whether there are spots, chew marks from insects etc.)
• Growth rate – measured with a ruler and recorded over a period
• Plant condition – poor, average, good or excellent
• Any pest or disease infection visible and the stage of infection
• Weed status and stage of development

Upon regular inspection, the farmer can visit each of the monitored plants and monitors their condition for the above features. These results of monitoring must be recorded, even if it is only recorded that plants are healthy. If the condition of the plants changes over time, any problem that develops can be managed as soon as it develops.

Regular monitoring of crops is important as it allows the farmer to distinguish between old damage on leaves and fruits that has already been treated, and new damage that might need treatment. For example, grape vines may suffer from mildew in late spring when humidity is high. The farmer will treat the crop with a fungicide to destroy the mildew. On revisiting the crop in late summer, damage on the leaves of the grape plant will remain, even though the disease has been treated. Regular monitoring of crops makes it possible to differentiate between old and new damage and infection. Monitoring should also include environmental conditions like wind, rain hail and temperature readings.

Crop monitoring indicates the pest’s status and extent of the crop diseased. 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 select a suitable control action. In this way, the farmer can e.g. treat crops chemically as and when required instead of according to a strict spraying programme. In this way, the amount of pesticide applied, and labour inputs can be reduced, also reducing the crop production costs.

The monitoring process is generally known as scouting. Scouting is used to identify pest species present as well as the extent of infestation of the pest. This can also be applied to crop diseases. In the case of crop diseases, it is not always possible to identify a disease or revere it to an expert in diseases. Thus, when monitoring for crop disease, 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.

Pest control programmes are based on infestation thresholds as well as economic thresholds for pest control. This programme must also consider 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 considered in the monitoring process.

The monitoring process starts with surveys. Monitoring techniques exist to aid in crop survey.

The two most useful survey techniques: the trans-act and step-wise method, scouting or placement of traps. Both techniques require the investigator to walk through a field and at set intervals he stops, sampling, scouting or counting the area. 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 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.

Using the transect method; 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 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 infestation rates. Based on the identity of the pest and degree of infestations, taking in account the crop- and environmental information, a management strategy can be implemented.

At the pre-determined intervals, using any of the scouting methods, sampling techniques for insect collection can be used. Sampling techniques generally used in pest monitoring are explained below:

The Monitoring Process

Step 1: Scouting

Monitoring for pests is commonly known as scouting. Scouting is aimed at identifying any pests, such as insects or signs of disease, present and assess the potential of the insect or disease becoming a problem and estimate the extent of damage. Because different pests occur throughout the life of the crop (some pests destroy seeds, other destroys leaves and other destroys fruit), weekly inspections are recommended.

Scouting should occur before any control treatment is applied and again after treatment. This will indicate the impact of the treatment on the problem.

Pests such as grasshoppers can be observed, and their population size estimated by walking slowly through the field and making careful observations. Others, like fungal infections, or small insect like trips may require the use of a hand lens for observation. Monitoring for certain pests may require the use of specialized equipment or techniques such as nets or traps.

A large round net with a long handle can be used to sample flying insects on a crop. Walking along crop rows and swinging the net above the top of the crop will allow the capturing of flying crop-damaging insects. Insects can be collected in the bottom of the net for study and identification purposes.

Click here to view a video that explains crop scouting tips and tricks.

Step 2: Estimate Damage

Impacts on crops are calculated by estimating the percent leaf damage of the affected plants. Although the figure below is for sunflower leaves, the system can be used as a guide to estimate the percentage insect damage or percentage fungal infestation. If the picture of a leaf is used as the outline of a tree or crop plant, the system can be applied to score the extent of damage induced on a plant or tree.

Source: University of Missouri

The farmer will have a reasonable idea as to the extent of leaf or plant damage that the crop can tolerate. Different crops respond to different levels of damage. Therefore, it is important to have an accurate understanding of potential damage. Likewise, a certain number of insects on a crop is inevitable; an insecticide will not kill all problem insects. There will be a certain number of insects that can live on the crop that the farmer would consider an acceptable level

Step 3: Record

It is critical that all information gathered during scouting is accurately recorded. Information must be recorded before the application of the pesticide, and again after the treatment. These notes will be vital for you to be able to determine whether the crop treatment (such as pesticide application) was successful or not. Make sure that enough time is allowed for the treatment to become effective before the post treatment monitoring is conducted.

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.

Example Of A Datasheet

Click here to view a video that explains scouting and record keeping.

Ensure Hygiene

The spreading of weeds, disease and insect pests can be encouraged through poor hygiene practices on the farm.

The aspects that are important include:

• Cleaning equipment such as shoes, tools, tyres and vehicles between sites or infestations.
• Close examination of nursery plants, seed, and imported soil or media to be used on the crop.
• Screening of irrigation water where weed seed contaminates surface water transported in canals and rivers or stored in lakes or ponds.
• Control of weeds and seed sources around the field or site.