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Soybeans | Forages
| Cereals | Dry
Edible Beans |
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.
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.
Tools used to monitor crop development and pests vary with
the crop and the pest. Basic field scouting equipment includes:
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.
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.
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.
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.
Figure 10-1. Scouting Patterns
For Pests Uniformly Distributed Across the Field
For Pests Expected in Headlands or Outside Rows
For Pests Developing in Specific Areas of the Field
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.
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.
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.
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:
Note: The growth stages and populations of each weed
or pest species should be identified separately.
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.
For more information:
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