Field Scouting

Excerpt from Agronomy Guide for Field Crops (Chapter 1)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Introduction
2. Timing of Field Scouting Operations
3. Scouting Tools and Techniques
   • Number of Recommended Sampling Locations Based on Field Size and Pest - Table 1-1
4. Scouting Pattern
   • Length of Row Required for a Thousandth of an Acre at Various Row Widths - Table 1-2
5. Determining Plant Population and Pest Infestation Levels
   • Determining Plant and Pest Populations Using a "Hula" Hoop - Table 1-3
6. Recording Field Observations
7. Sample Handling and Submission for Diagnosis or Identification
8. Updates
9. Related links...

Introduction

Crop scouting is the regular examination of fields to accurately identify yield-limiting factors during the growing season. Scouting provides an objective summary of the crop condition and pest situation in a field. Factors limiting the productivity of a field often arise suddenly and must be corrected quickly to preserve the full yield potential of the crop.

Every field season should begin with the recording of vital field information on soil fertility and crop inputs on a field record form.This information, combined with regular field scouting, accurate identification and diagnosis of problems and a record of those observations, makes for a successful crop monitoring program. See field scouting form. The information obtained from field scouting is useful in determining if any immediate actions should be taken. The information recorded is also useful for future reference to avoid problems in subsequent years. For example, a disease such as soybean cyst nematode impacts both crop rotation and variety selection when soybeans are grown again in the same field. Accurate records will aid in the decisions required to help manage this disease.

| Top of Page |

Timing of Field Scouting Operations

Early recognition of pests and their control will minimize their economic impact on the crop. Under each commodity chapter within this publication, crop scouting calendars illustrate the timing associated with the common crop insects and diseases found in Ontario. It is important to monitor fields consistently and frequently since pest dynamics can change rapidly throughout the season. As optimum plant populations are critical for achieving good yields, evaluate crop stands within 1-2 weeks of plant emergence. Early in the growing season, scout weekly. When approaching a control threshold, such as the application of a post-emergent herbicide or a fungicide, fields may require scouting daily. Later in the season, bi-weekly scouting is normally sufficient. Keep in mind that some insects and diseases occur later in the season and may approach control thresholds in a matter of days. Examples of such pests include armyworm, grasshoppers and stalk rots. If field and weather conditions favour these later-season pests, scouting should continue weekly.

| Top of Page |

Scouting Tools and Techniques

• a clipboard with field scouting forms or a notebook
• field maps
• a shovel
• a pocketknife
• plastic and paper bags for collecting specimens
• a 10X hand lens and a sampling frame (i.e., hula hoop)

Other tools could include aerial field images, a camera, labels for identification, reference guides, a sweep net, vials and isopropyl alcohol, sticky cards or traps to detect insect pests, a GPS unit to mark the location, flagging material, etc. It is also wise to wear appropriate clothing for protection from the sun and from unknown risks such as poisonous plants and mosquitoes. Be aware of recent pesticide treatments applied to the field and obey re-entry intervals indicated on product labels.

When scouting for insects that move too quickly in the canopy to be spotted at a glance, it is sometimes easier to use the beat cloth or sweep net. A beat cloth can be spread on the ground between two rows of crop. The crop can then be pulled over the cloth and shaken vigorously so that any insects on the plant are dislodged onto the cloth. The insects can then be easily identified and counted.

A sweep net is the preferred scouting method when evaluating a solid stand crop like alfalfa or solid stand soybeans. Standard 37-cm (15-in.) diameter sweep nets are available commercially through the various companies listed in Appendix A, Insect-Monitoring Equipment Supply Companies. While walking through the canopy, swing the net from side to side in a pendulum-like motion, across the top of the canopy so that the top of the net is at the top of the canopy. Avoid dirt collecting in the net by not digging into the ground during the sweeping procedure. Bringing the net across and back to the home position is considered one sweep (e.g., sweep right to left and back again for one sweep). After 20 sweeps, quickly close the top of the net by grasping it just below the opening. Slowly open the net, remove any plant debris collected and count the number of insects that have been captured. Though sweep nets will not give an absolute number, they will provide a relative estimate of insect pressures, allowing for a quick assessment of the presence of a particular insect.

| Top of Page |

Scouting involves walking through a field and stopping at a number of locations to make observations. The number of sampling locations in a field depends on factors such as field size, crop, pest, etc. The general number of sampling locations for a range of field sizes is displayed in Table 1-1, Number of Recommended Sampling Locations Based on Field Size and Pest. For scouting purposes, fields larger than 16 ha (40 ac) should be split into units of 16 ha (40 ac) or less.

| Top of Page |

Scouting Pattern

There are a few factors to consider when determining what scouting pattern to follow in your field.

• Use a scouting pattern that includes changes in variety/hybrid, soil type, past cropping history, fertilizer/manure application and any other factors that can affect plant growth. The pattern should cover all parts of the field and should vary each time the field is scouted. See Figure 1-1, Scouting Patterns.
• Sampling locations should be selected on the basis of a predetermined random pattern, as opposed to factors such as crop appearance, etc.
• Start scouting at least 20 m (66 ft) into a field. Outside rows and headlands should be avoided in the scouting pattern unless there are specific reasons for sampling these areas.

| Top of Page |

Figure 1-1. Scouting Patterns

Pests Uniformly Distributed Across the Field

When scouting for pests or problems that you expect to occur uniformly in the field or for pests and problems whose distribution pattern is unknown, distribute the sampling locations evenly across the field as shown above. This pattern is also appropriate for soil sampling.

Pests that fit this scouting pattern include corn rootworm, European corn borer and stalk rots.

Pests Expected in Headlands or Outside Rows

When scouting for pests or problems that you expect to appear on headlands or in outside rows, distribute the sampling locations evenly around the edges of the field, as shown above.

Pests and problems that fit this scouting pattern include armyworm, spider mites and soil compaction.

Pests Developing in Specific Areas of the Field

When scouting for pests or problems that you expect in particular parts of a field, concentrate sampling locations in areas where the problem or pests are most likely to be found, as shown above.

Pests that fit this scouting pattern include Phytophthora root rot in damp clay soils and black cutworms in weedy patches.

| Top of Page |

Determining Plant Population and Pest Infestation Levels

Plant population and some pest infestation levels are determined by making counts in areas of a given size and then multiplying that number by a factor to obtain the population per acre. For row crops, plant population can be calculated by counting the number of plants in a thousandth of an acre and then multiplying the count by 1,000 to obtain the number of plants per acre. Table 1-2, Length of Row Required for a Thousandth of an Acre at Various Row Widths, lists the row length equal to a thousandth of an acre at various row widths.

¹To obtain the number of plants per hectare, multiply the number of plants per acre by 2,470.
*See Updates section below.

To determine plant population in narrow-row crops or weed infestation levels, a sampling frame with a known area can be placed on the ground for the counts. This can be accomplished using a square frame (e.g., 50 cm x 50 cm = 0.25 m2) or circular frame (e.g., a hula hoop). The "hula" hoop method is displayed in Table 1-3, Determining Plant and Pest Populations Using a "Hula" Hoop. By using the table, the number of plants/ha (plants/ac) can then be determined by measuring the diameter of the hoop, counting the number of plants that are found within the hoop and multiplying that number by the predetermined factor listed for the inside-hoop diameter.

| Top of Page |

Many insect action thresholds are expressed as the average number of insects per plant, per sweep, per square metre or per foot of row. Some may also be based on a percentage of defoliation or damage. Regardless of the method used, at least 10 random counts should be taken in each field to determine average populations.

| Top of Page |

Recording Field Observations

Field scouting records are an essential tool to use for both current and future management decisions. Using a field scouting form will facilitate and standardize the recording of field observations. Once recorded, the scouting data should be added to the field record files. Computer software is also available to record and manipulate data from field observations.

Information to be recorded should include:

• field location and scouting date
• growth stage and condition of the crop
• hybrid/variety planted and whether it's resistant or transgenic
• flowering, tasselling, heading dates
• weather conditions
• soil conditions
• weed species present, location and population
• diseases present, location and population
• insects present, location and population
• crop damage
• field map
• results of scouting procedures performed
• action required

| Top of Page |

Sample Handling and Submission for Diagnosis or Identification

It may be difficult to identify a pest or field problem, or you may require diagnosis and assistance. In these situations, send samples for analysis to diagnostic laboratories. For more information on how to take proper samples, where to obtain sample submission forms and diagnostic service fees, see Appendix L, Diagnostic Service.

Updates on Field Scouting

Addition to Table 1-2 footnote - "To obtain the number of plants per hectare, multiply the number of plants per thousandth of an acre by 2,470."

OMAFRA Publication 811: Agronomy Guide for Field Crops Table of Variance

Related links...

• Integrated Pest Management

| Top of Page |