Carmen Blubaugh, Washington State University
This eOrganic video on scouting vegetable crops was created by members of a project of the USDA National Institute of Food and Agriculture, Organic Agriculture Research and Extension Initiative (NIFA OREI) entitled Biodiversity and Natural Pest Suppression (BAN-PestS).
Watch this video clip at https://www.youtube.com/watch?v=IkixPtTTXyA
What was the last crop you lost to a pest? When did you realize you had a problem? Many times we don’t know there is a problem until we are up close and personal with a crop. All too often that is at harvest.
Scouting is the routine monitoring of pest pressure in a crop. A scouting routine can help you identify problems in your field before they get out of control. In this video we will scout for cabbage aphid in brassica crops in the Pacific Northwest. However, the scouting principles and tips can apply to any crop or region.
What is Scouting?
Scouting is a systematic way to assess the health of your crop and threat of pest outbreaks without examining every plant. Scouting relies on sampling a subset of the field to collect data you can use to make informed management decisions. Scouting can reduce your inputs and crop losses, saving you money.
There are various tools used in scouting. The tool you will use depends on the crop and pest. Many pests must be trapped to monitor while others, such as cabbage aphid, can be observed on the crop without trapping. In this video we focus on visual observation, but many of the principles of scouting we cover will apply regardless of the scouting tool used.
To begin a scouting routine, start by researching the pests you are likely to observe and the corresponding beneficial insects. This information will help you identify which scouting tools are appropriate and when to begin scouting. Numerous extension resources are available that describe the community of pests associated with a particular crop in your area.
Scouting 101: Before Entering the Field
When you arrive at the field, commit your attention to scouting. Focus is required to capture signs of pests. First, make observations about the entire field. Look for areas that appear stunted or have a color variation. Notice any unique geographic features, such as a depression. These areas may have higher pest pressure. You will want to visit these areas.
Select a path through the field that will allow you to collect a random yet representative sample. One method is to travel through the field in a "w" pattern, selecting plants to sample randomly along that path. Adjust your path through the field to ensure you visit areas you have identified to be at higher risk for pest infestations. Record your path through the field so that on your next visit you can scout a different route. Each scouting trip, you will select a different random sample. On each scouting trip you may want to visit areas you suspect to have growing pest populations in addition to your random sample.
In the Field
When you reach your first sample, assess the plant overall and then start looking at the individual leaves. Look at both young and old leaves, and don’t forget to search both sides of the leaf. You will want to remove a few leaves for closer observation. Now look at any buds, flowers, or fruit. Depending on the potential pest, you may even use your harvest knife to cut open the stalk or unearth the plant so you can see the roots.
Record your observations and a numeric assessment of the pest. For example, a numeric assessment of cabbage aphid pressure is the average number of aphids per leaf. Select three leaves from different parts of the plant and record the number of aphids and aphid predators per leaf. Repeat for ten plants.
You will follow the same procedure each time you scout, but vary your path through the field and which plants you sample. Standardizing your collection method is necessary to accurately track pest pressure over time.
Calculate the average number of aphids and predators per leaf. Reviewing these averages from visit to visit allows you to determine whether or not the pest pressure is increasing, or if beneficial insects are effectively managing the pest. This information will allow you to determine if and when you need to take action to control the pest, in other words, your action threshold.
Your action threshold is the point at which you’ll experience economic loss if control measures are not pursued. Your action threshold depends on the cost of controlling the pest, the effectiveness of your control measure, the value of your particular crop, and the potential for the pest to cause damage that will impact your ability to sell the crop. These factors vary for different crops. For instance, tolerance for aphids may be higher on kale than broccoli since aphids can get into broccoli heads where they are protected from insecticide applications.
Action thresholds also change over time, as markets fluctuate. Ask your local extension educator for help identifying a recently published action threshold for your region and crop. Keep in mind that action thresholds are usually calculated without considering biological control by beneficial insects, and you may want to adjust your action threshold if you observe high rates of natural pest suppression.
Developing your Scouting Routine
Farming is a demanding occupation. To make sure scouting gets done, it is best to make scouting a habit. Tip: For best results, scout twice a week. For instance, you could dedicate lunchtime Tuesday to scouting a few fields. Keeping a bucket of scouting tools easily accessible can help facilitate regular scouting. Must-have scouting tools include a pencil, paper, clipboard, tally counter, and camera.
Pest emergence and growth are each temperature-dependent, and vary with each crop. Check local extension resources to determine approximately when pests in your crop system emerge, and initiate your scouting routine accordingly.
Scouting is an important practice to do on your farm that will definitely pay off. Check out the Pacific Northwest Insect Management Handbook for up-to-date information on crop specific pests. There, you’ll find examples of action thresholds, local emergence times and other resources to help you prepare for and avoid pest outbreaks on your farm.