Field Scouting
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| Cereals | Dry
Edible Beans |
| Spring and Winter Canola
| Other Crops | Soil
Management |
| Soil Fertility and Nutrient
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| On-Farm Stored Grain Management
| Weed Control |
| Insects and Pests of Field
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Pub 811:
Agronomy Guide> Field
Scouting
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811: Agronomy Guide for Field Crops
Table of Contents
Field Scouting
Field scouting involves walking through a field and stopping
at a number of locations to make observations. Regular field examinations
help to accurately identify yield-limiting problems during the growing
season when they can often be corrected so that full yield potential can
be preserved. Every cropping season should begin with the recording of
vital field information (soil fertility and crop inputs) on a field record
form. Example field record forms are available on the OMAFRA
website. 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. In addition to dealing
with immediate issues, record scouting information for future reference
to avoid problems in subsequent years. For example, a pest 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 pest.
Timing of Field Scouting Operations
Early recognition of pests and their control will minimize
their economic impact on a crop. Under each commodity chapter within this
publication, crop scouting calendars illustrate the timing associated
with the common crop pests 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, soybean aphids and stalk
rots. If field and weather conditions favour these later-season pests,
scouting should continue weekly.
Scouting Tools and Techniques
Tools used to monitor crop development and pests vary with
the crop and the pest. Basic field scouting equipment includes:
- a clipboard with field scouting forms or field pocket guide to record
observations
- 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)
Professional scouts often carry other tools that 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 drop cloth or sweep net.
A drop 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 identified and counted.
Using Sweep Nets
A sweep net is the preferred scouting method when evaluating a solid
stand crop such as alfalfa, canola or solid seeded 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 sweeping across
the top 37 cm (15 in.) of the canopy. Avoid collecting soil in the net
by not digging into the ground during the sweeping procedure.
There is some confusion as to what is considered a single "sweep"
in many of the thresholds established in pest management. Some researchers
set thresholds based on the definition of one sweep consisting of two
180° arcs bringing the net across from one side of the body to the
other and back to home while walking slowly forward. Other researchers
established thresholds based on one sweep consisting of only one 180°
arc bringing the sweep net only from one side of the body to the other,
once, (which is exactly half of what the others considered a sweep). It
is therefore important to determine which definition of a sweep has been
used for each threshold recommendation, before determining pest populations
in a field.
If the incorrect definition of a sweep for a threshold is used, over-
or underestimation of the average number of insects per sweep can occur.
In this publication, the definition of a sweep (i.e., either a 180°
arc or two 180° arcs) is defined for each threshold if it is known.
After completing the indicated number of sweeps, quickly close the top
of the net by grasping it just below the ring. Slowly open the net, remove
any plant debris collected, identify and count the insects that have been
captured. Repeat this in five areas (or the number identified in the threshold)
of the field to get a good assessment of population levels across the
field. 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.
Number of Sampling Locations
The number of sampling locations in a field depends on factors such as
field size, crop, pest type and stage of development, level of infestation,
timing, etc. The general number of sampling locations for a range of field
sizes is suggested in Table 10-1, Number of Recommended
Sampling Locations Based on Field Size and Pest. For scouting purposes,
fields larger than 16 ha (40 acres) should be split into units of 16 ha
(40 acres) or less.
Table 10-1. Number of Recommended Sampling
Locations Based on Field Size and Pest
| Field Size |
Number of Sampling Locations |
|
(hectares)
|
(acres)
|
Insects/Diseases
|
Weeds
|
|
Up to 8
|
Up to 20
|
5
|
10
|
|
8 to 12
|
20 to 30
|
8
|
15
|
|
12 to 16
|
30 to 40
|
10
|
15
|
Scouting Pattern
The scouting pattern should cover all parts of the field and observation
locations should vary each time the field is scouted. However, when hot
spots are identified, recheck them to monitor the development of the pest.
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
10-1, Scouting Patterns.
- Select sampling locations 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. Avoid outside rows
and headlands in the scouting pattern unless there are specific reasons
for sampling these areas (e.g., armyworm moving from cereal into corn
fields).
Figure 10-1. Scouting Patterns
For Pests Uniformly Distributed Across the Field
- Randomly select 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.
For Pests Expected in Headlands or Outside Rows
- Randomly select 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.
For Pests Developing in Specific Areas of the Field
- Concentrate sampling locations in areas where the problem or pests
are most likely to be found, as shown above, but also monitor other
areas of affected fields.
- Pests that fit this scouting pattern include phytophthora root rot
in damp clay soils and black cutworms in weedy patches.
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.
Table 10-2. Plant Populations at Various
Row Widths
| Row Width |
Length of Row Equal to 1/1,000 acre1,2 |
| centimetres |
inches |
metres |
feet |
|
38
|
15
|
10.6
|
34 ft. 10 in.
|
|
51
|
20
|
8.0
|
26 ft. 1 in.
|
|
56
|
22
|
7.3
|
23 ft. 10 in.
|
|
71
|
28
|
5.7
|
18 ft. 8 in.
|
|
76
|
30
|
5.3
|
17 ft. 5 in.
|
|
81
|
32
|
5.0
|
16 ft. 4 in.
|
|
86
|
34
|
4.7
|
15 ft. 5 in.
|
|
91
|
36
|
4.4
|
14 ft. 6 in.
|
|
97
|
38
|
4.2
|
13 ft. 9 in.
|
1 To obtain the number of plants per one-thousandth hectare,
multiply the number of plants in the length of row by 2.47.
2 Multiply the number of plants counted in the length of row
above by 1,000 to determine the number of plants/acre.
For row crops, plant population can be calculated by counting the number
of plants in a thousandth of an acre (1/1000), then multiplying the count
by 1,000 to obtain the number of plants per acre. See Table
10-2, Plant Populations at Various Row Widths.
To determine plant population in narrow-row crops or weed/insect infestation
levels, a sampling frame with a known area can be placed on the ground.
Count all pests or weeds within the area of the frame. This can be accomplished
using a square frame (e.g., 50 cm x 50 cm = 0.25 m2) or a circular frame
(e.g., a hula hoop). The "hula" hoop method is presented in
Table 10-3, Hula Hoop Method for Determining Plant
and Pest Populations.
Table 10-3. Hula Hoop Method for Determining
Plant and Pest Populations
Inside Diameter
of Hoop in Centimetres (inches) |
Area in
Metre2 (ft2) |
Factor by Which to Multiply
the Number of Plants
Within the Hoop to Equal: |
|
Plants per Hectare
|
Plants per Acre |
|
91 (36)
|
0.65 (7.0)
|
15,385
|
6,165
|
|
84 (33)
|
0.55 (6.0)
|
18,182
|
7,334
|
|
76 (30)
|
0.45 (4.9)
|
22,222
|
8,874
|
|
69 (27)
|
0.37 (4.0)
|
27,027
|
10,956
|
|
61 (24)
|
0.29 (3.2)
|
34,483
|
13,865
|
|
Inside dimensions of a square frame in centimetres
(in.)
|
|
50 x 50
(20 x 20)
|
0.25 (2.7)
|
40,000
|
16,133
|
|
100 x 100
(40 x40)
|
1.00 (11.1)
|
10,000
|
3,924
|
Count the number of plants that are found within the hoop or square and
multiply that number by the pre-determined factor listed above to determine
plant population per hectare or acre.
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, take at least 10 random counts in each field to determine
average populations. Record each count and then take the average of all
counts as the estimate of the field pest population.
Recording Field Observations
Field scouting records are an essential tool for making current and future
management decisions. Using a field scouting form will facilitate and
standardize the recording of field observations. Once recorded, add the
scouting data to the field record files. Computer software is also available
to record and manipulate data from field observations.
Information to be recorded during scouting events includes:
- field name/code, 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, growth stage, location and population (including
any natural enemies present)
- diseases present, growth stage, location and population
- insects present, growth stage, location and population
- crop damage
- field map
- results of scouting procedures performed
- action required
Note: The growth stages and populations of each weed
or pest species should be identified separately.
Sample Handling and Submission
It can be difficult to identify a pest or field problem. Seek diagnosis
and assistance from other resources, including experts and/or diagnostic
laboratories. For more information on how to take proper samples, where
to obtain sample submission forms and diagnostic service fees, see Appendix
I, Diagnostic Services.
