Food for thought: the Scout decision

In 1907, Baden-Powell, an English soldier, devised the Scout motto: Be Prepared. That’s always a good plan in all areas of life, including the horticultural sector, where pests and diseases can have devastating effects on crops and on the grower’s bottom line.

Both greenhouse and outdoor crops are susceptible to many pests and diseases which cause irreversible damage and can lead to serious economic losses. Because of the low tolerance for damage, ornamental crops require regular scouting and an effective pest management strategy to ensure that a higher marketable quality is maintained.

A good crop scout can be a valuable asset to a grower. If no scouting function is performed, there is little or no chance of early problem detection and identification. Growers need to keep a close eye on each field throughout the growing season to avoid crop losses.

The cornerstone of an Integrated Pest Management (IPM) program is scouting or monitoring plants for insects, diseases, weeds, nutrient deficiencies, physiological problems and overall crop health. Crop scouting keeps a grower on top of field conditions, helps in catching and diagnosing problems early and allows for timely corrective action to protect crop yield and quality. When done regularly, crop scouting is a valuable tool for identifying field-specific pest pressure and crop injury in order to prevent potential outbreaks from occurring, which reduces crop damage and plant losses.

Scouts collect up-to-date information regarding the presence of pests (primarily insects and diseases) and evaluate the effectiveness of previous pest management strategies. Scouts need to have a good understanding of plant biology, pest biology, pest life cycles, host plants, beneficial insects, injury symptoms, environmental risk factors, and control strategies. With proper training and experience, scouts can identify potential problems and provide the information necessary for making good pest management decisions.

The method used by a professional scout is a straightforward one, in which the scout monitors the crop by examining a representative sample of the plants. First the area to be scouted is mapped and, if large divided into sections. When the scout monitors the crop, he/she looks at plants that are at high risk of being infested/infected: along walkways, by doors, along outside rows, and in areas where infestations/infections have been previously found. The rest of the section is covered in a zig zag random pattern. The part of the plant a scout examines is determined by the behavioural characteristics of the pests most common to the plant. As the scout finds problems, he/she uses a record sheet to note his/her findings and marks any infestations/infections on the map.

Pest management professionals will use information provided by the crop scout to select and implement a pest management program. A well-designed scouting program includes three main activities:

1. Sampling to provide an accurate estimate of pest densities and crop health.
2. Identification of pests or diagnosis of the cause of crop injury based on observable symptoms.
3. Comparison of observed pest pressure or crop injury to recommended economic injury levels or economic thresholds.

Thus, the success of the recommended pest management procedures depends on the accurate and timely completion of all three crop-scouting activities.

Scouting should be done weekly during the growing season but this can vary according to the crop grown, the stage of growth, the perceived pest threat, and weather conditions. Scouting for a particular pest or problem requires very specific methods. These methods can vary depending upon the pest or problem, but may include time of day, stage of crop, location to look on the plant or in the soil, as well as action population thresholds.

Fields are scouted to determine whether one or more pest management tactics are justified. The benefits of scouting include;

1. To improve pesticide application decisions based on scouting reports; right timing and targeting.
2. Increase control of pests and to manage resistance of pests to chemicals.
3. To avoid economic losses to the grower.
4. Improved selection and evaluation of application techniques.
5. Permit the use of biological control agents.

The concept of an economic injury level was developed to provide objective guidelines for making informed decisions about pesticide use. The economic injury level is the pest density or level of crop injury that will result in yield loss equal to the cost of managing the pest. It may be considered the break-even point, or the lowest pest density at which treatment may be economically justified. The economic threshold is the pest density or level of crop injury at which controls should be applied to prevent an increasing pest population from reaching the economic injury level.

Flower growers can optimize pesticide usage, maximize economic returns, and produce high quality crops by using IPM programs which use established scouting procedures. The horticultural sector will continue to expand into more specialized and diverse areas and as a result, growers need to be ‘be prepared.’ Crop scouting will play an even more vital role in the business of agriculture.