Tobacco Insect Scouting Methods
Why should you scout insects in tobacco?
It is necessary to know the density of insects and their damage (per plant or per acre) to determine if and when insecticide treatments are necessary. Insects should only be treated when their densities exceed recommended economic thresholds. This practice ultimately saves money, protects workers and the environment, and has the potential to reduce pesticide residues by avoiding unnecessary applications Treating only when insects reach thresholds is also a key component of integrated pest management (IPM) practices required as part of tobacco GAP programs.
What are economic thresholds?
The economic threshold is the point at which plants should be treated to avoid damage that will result in monetary loss. Economic thresholds are set below the economic injury level (EIL), which is the point at which the cost of management is less than the loss incurred due to insect damage. Therefore, economic thresholds are conservative in recommending action before economic loss has occurred. See Radcliffe’s IPM World Textbook for a detailed description of economic thresholds and economic injury levels.
How do you scout insects in tobacco?
Tobacco fields should be scouting weekly following transplant through harvest. Current tobacco scouting recommendations suggest using the following sampling scheme, based on field size:
- Very small fields (1-3 acres): Make 8 stops, randomly distributed throughout the field. At each stop, observe 5 plants for a total of 40 plants across the field.
- Small fields (4-8 acres): Make 10 stops, randomly distributed throughout the field. At each stop, observe 5 plants for a total of 50 plants across the field.
- Large fields: For each 4 acres a field exceeds 8 acres, add 2 stops (observing 5 plants at each stop). For example, in a 20 acre field, you would add 6 stops, for a total of 16 stops with 80 plants observed across the field. In a 100 acre field, you would add 46 stops, for a total of 56 stops with 280 plants observed across the field.
The more stops you make, the more accurate your scouting data will be. Fields should be scouting as they will be managed. If you will treat a field as a single unit, scout the acreage of the entire field. If the field is bisected by natural barriers, such as waterways or woods, and it will be managed as separate units, scout each section separately. Scouting locations within a field should be selected randomly to avoid bias. You can use a random set generator to create a random number table, which you can use to guide the number of rows and plants you will move after each stop. When scouting key tobacco insect pests, know how to identify them, when they are likely be active during the growing season, what plant part they are likely to injure, and the appropriate economic thresholds.
Record the number of insects per plant or the percentage of infested plants for each field and keep these records. An example of the type of scouting record we keep is here (Generic Scouting Sheet), and the scouting records from the Tobacco GAP Manual are available under “Records” at their site. GAP inspectors may ask to view these records. Also record what, if any, action was taken against pests and the outcome of that action. This information will be useful when making future management decisions.
When to scout for key tobacco pests
Not all tobacco pests are active at all times, so scouting efforts can be optimized by only observing pests that are likely to be active during a given growth stage or time of year.
The pest-specific scouting guidelines below include a section on when to scout for each key pest.
Scouting methods for key tobacco pests