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Crop Scouting - Controlling Pests & Diseases

Crop scouting controls pests while increasing profit potential.

Crop scouting is a tool that farmers have been using for generations. Today, scouting is a crucial component of Integrated Pest Management (IPM) systems designed to be a more effective method in battling pests.

How to scout

It would seem as though the term crop scouting would be pretty self-explanatory. You should just keep an eye on your fields, right? However, crop pest scouting should be a well-planned program, and it often requires extensive record keeping and data gathering as well as an investment in time. In fact, many growers hire professional scouts or agronomists to manage their scouting program. Southern States offers an aerial imagery program service to help growers in this task.

Growers should begin monitoring fields early in the season, even before planting, before visible weeds or insects are present. Typically, fields are scouted once a week. However, the time of year, crop and pest potential determine how often scouting is needed. For example, when growing cotton, experts recommend scouting every 5 days from the pinhead square to cut out phases, as insects are most likely to attack during this critical time.

The path in the field you take when scouting also needs to be considered. The field should not be entered at the same place each time. Your path should vary each time as well. The scout should walk to within 50 feet of every border, as borders are more likely to be infested than the interior. In their records, some growers find it helpful to draw maps of their field in order to follow a different path every time. With today's technology, it may also be advantageous to use a camera, smartphone or tablet to take pictures of potential issues and their locations for review after leaving the field.

Taking samples

The size of the field should determine how many stops are made and, if necessary, the number of samples taken. Please see below for a generally suggested number of stops by the size of field.

Field Size by Acres Number of Insect Stops Number of Weed Stops

Up to 20









Over 50

Split into two fields

Split into two fields

Insect pests

When observing insects, there are different methods you can employ to ensure you are gathering the right information. Direct observation is one method; this is more effective for small plants as it becomes more difficult to determine accurate insect counts as plant stands grow denser.

You can also use sweep nets and drop cloths to collect insects. This method allows the scout to sample for many pests at once. However, the results are not always accurate, as the insects per sweep are not necessarily a direct measure of the population per area. Also, results from the sweeping method can vary depending on the person performing the task.

Farmers also use insect traps to collect samples. This method is effective at trapping certain insects, but it may miss possible pest thresholds that don't enter the trap.

Disease and plant health issues

Scouting can also indicate if plants are having any health issues and if disease protection is needed.  The plants might have a nutrient deficiency that needs to be addressed, or they may be battling a disease that needs treatment. Look for discolored leaves, stunted plants, stand failure, foliage burn or split stems.

Treatment thresholds

When scouting for pests, it is important to know treatment thresholds; even if there is a pest situation, it might not be economically significant enough to warrant treatment with expensive products and application.

The action threshold (AT) is a pest population level reached after which pest management will prevent economic loss. The economic injury level (EIL) is the point where pest control measures equal any loss of income due to damage caused by pests.

There is a formula you can use to help determine the EIL: EIL = C / ( V x I x D ), where:

  • C is the cost of the pest management alternative by acre
  • V is the value of the crop sold by unit (bu., ton, bale, puond, etc.)per acre
  • I is the extent of the injury, or percentage of loss per acre
  • D is the damage per injury amount, or the expected yield of the crop before disease per unit by acre

When the EIL is less than one, treatment is cost-effective because it is less than the loss of income from pest damage.

Staying on track

Keeping detailed scouting records helps predict what pests might affect your fields in the future and identify certain hot spots that might be more susceptible to pests. Recordkeeping will also help determine if threshold levels are met and past treatment methods employed.

With insect populations, experts advise growers to keep track of beneficial insects along with harmful insects. You could overestimate the harmful pest population if not factoring in the positive impact from beneficials.
Reviewing past records of weeds can be helpful when determining current and future treatments. Knowing if those types of weeds were present can impact planning in the new growing season.

Overall, the steps needed to provide crop protection from disease, weeds, and insects are determined from scouting. Scouting also provides the information to determine if curative measures are needed.

For more information, consult with your Southern States Agronomy Expert. Many University Extension programs have scouting guides specific to their states. Extension also provides local updates and alerts, as well as threshold information through websites and phone hotlines. Please see the links below:

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