Top Crop Manager

Features Agronomy Insect Pests
Commitment to crop scouting pays dividends

Knowing the distribution and movement patterns of a pest can help target strategies.


November 19, 2007
By Top Crop Manager

Topics

Active and thorough crop scouting is an important and efficient tool to help
ensure crops reach maximum yields. But that is only part of the story, say crop
experts. Scouting fields also helps plan crop rotations, predict agronomic problem
areas and evaluate overall management decisions and operation productivity.

When field scouting is done effectively, growers should be able to identify
problems early and then determine the most economical solutions. The information
gathered from scouting also contributes to efficient crop scouting and management
decisions for subsequent seasons.

Record keeping is a key to crop scouting success. With accurate records, growers
can follow the development of potential pest populations. This allows growers
to prevent or effectively react to crop production issues and make accurate
in-season applications when needed. "Regular scouting and note taking helps
to monitor how pest populations change, allows you to identify increasing or
decreasing trends and helps determine if control practices are needed,"
says Manitoba Agriculture, Food and Rural Initiatives entomologist John Gavloski.

"Record keeping is absolutely critical to help growers anticipate problems
like weeds or herbicide carryover. It also helps you be a sharper manager,"
adds Denise Maurice, Agricore United's technical development manager, crop protection,
based in Calgary, Alberta.

According to Gavloski, scouting should be done as often as possible –
at least once a week, if manageable. Fields may need to be scouted more frequently
if a pest is approaching economic threshold or conditions favour rapid pest
growth. "The earlier you can start scouting the better," he says.
For some pests, such as wireworms, it may be helpful to scout fields before
seeding to help determine appropriate seeding practices and seed treatments.
Common pests also dictate when to scout. "For example, growers need to
look for cutworms immediately after crop emergence, and look for grasshopper
populations along field edges in early June, at the latest, before grasshoppers
develop wings and begin to disperse."

When scouting fields it is important to look for recurring problems, but growers
should also consider all potential issues, both pest and crop vigour related.
"This will keep you from narrowing your focus and overlooking new, yield
limiting factors," explains Agricore United CCA and Agronomic Crop Enhancement
(ACE) specialist Keith Mills.

To properly evaluate all potential agronomic yield reducing issues, it is essential
to do a thorough scouting. "Walking 20 feet into a field doesn't qualify
as a thorough scout," says Maurice. "Growers should walk a 'zig-zag'
or 'W' pattern across the entire field to gather an accurate representation
of the field and also scout problematic areas like low spots or knolls."

Knowing the distribution and movement patterns of a pest can also help target
crop protection strategies and save money. "Some insects have edge effects
or are located in concentrated patches," says Gavloski. "As a result,
growers may be able to gain control with a spot spray. But, if the insect is
not spreading or is past its damaging stage, not spraying may be the most economical
option."

Accurately assessing the stage of development of the crop, weeds and insects
often determines the effectiveness of the crop protection application. "Staging
is one of the most important aspects of crop scouting and is critical to optimizing
return on the herbicide or insecticide application," says Maurice.

With respect to insects, Gavloski further notes that observing the stage of
both the potential pests and the crop is important because certain insecticides
have a narrow window of effectiveness. "For example, for optimum control
of grasshoppers, control measures need to be applied before grasshoppers become
adults. With wheat midge, however, insecticides will only control the adults,
making an application economical only during a certain stage of wheat growth,"
explains Gavloski.

When identifying the weed stage it is also important to assess the rate of
crop development. This will determine whether the crop will out-compete the
weed species or if a herbicide application is required. "Herbicides generally
have a specific window of effectiveness and once weeds have past an optimum
stage, herbicide applications can become costly," says Mills. "Crop
staging is vital with herbicides because applications before or after the recommended
application stage can cause crop damage and impact yield."

When scouting, growers should record as much information as possible including
when they scouted, which field, soil type and crop they scouted. Also record
the pests present – their stage, density and distribution – as well
as environmental conditions, problem locations and where samples were taken
from.

There are a number of tools and resources growers can use to help optimize
crop scouting. The provincial agriculture ministries as well as retailers like
Agricore United have a wide selection of resources such as pest identification
guides, record keeping booklets and fact sheets.

Growers can also access valuable information on provincial ministry web sites.
For example, Gavloski reports that Manitoba Agriculture actively monitors weather
and wind patterns and their effect on insect populations. In 2005, Manitoba
Agriculture will be part of a new, prairie-wide pest monitoring network, which
will monitor and provide regularly updated forecasts for pests such as diamondback
moth and bertha armyworm. Growers and agronomists will have on-line access to
pest distribution maps to help determine current populations and alert them
to potential threats for their local area.

Maurice also notes that an Agricore United program – AgroManager –
is available for growers and includes a field record keeping system to track
legal land locations, soil test results, identify prevalent pests, crop and
weed stages, crop protection and crop nutrition history. The program can also
generate economic loss projections based on agronomic and pest pressures for
a specific field condition.

When scouting, Gavloski recommends growers have access to a sweep net, a device
to measure a metre square, hand lens and containers for specimen collection.
Tools like the sweep net and metre square are essential to identify damaging
populations of small, hard-to-see insects, such as the lygus bug, and to take
accurate weed counts for determining economic thresholds.

For assistance with crop scouting, growers can also contact their local crop
advisor. Working with a trained crop scout or agronomist can help growers determine
the most economic and effective crop protection measures to ensure maximum yields
are achieved.

Stay ahead of problem pests
Crop scouting is most effective if done on a regular basis.
Weekly scouting is recommended, but is not always possible. If time is
limited, Agricore United's Keith Mills recommends growers focus on seven
key periods during the crop year.

Pre-seed
Look for obstacles to healthy crop emergence. Scout for weeds that start
early and will be difficult to control in crop, soil crusting, poor seedbed
quality, seedling damaging insects like wireworms and wet spots.

Post-emergence
Evaluate emergence, crop vigour and plant stand. Also look for seedling
damaging pests like cutworms, wireworms, flea beetles and emerging weeds
that will compete with crop seedlings.

Pre-application
Before application, ensure accurate identification of insects and weeds,
their stage, distribution and density. This will help determine if a herbicide
or insecticide application is economical and which product will be most
effective.

Post-application
Scout one to two weeks after an application to determine if the product
is working or if a second application is needed. At this point, fertility
concerns – sulphur deficiencies in canola and nitrogen deficiencies
in cereals – will become evident and can be corrected.

Early heading or flowering
Scout for and control diseases such as sclerotinia in canola and late
season insects like lygus bug and diamondback moth.

Pre-harvest
Plan a harvest schedule based on crop maturity as well as provide an opportunity
to manage perennial weeds.

Post-harvest
Identify and plan for potential issues the following year and provide
another option for management of perennial weeds, straw management and
over wintering insects and weeds. A post-harvest scout should also include
soil sampling to plan for crop nutrition requirements.

 

 


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