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Soybean Information Package
So, you’ve decided to grow soybeans! Whether it’s your first time growing them, or you’ve
tried it a time or two, hopefully the following pages will have something in them that you will
find interesting and helpful.
Field selection
Soybeans can be grown on many different soil types, although the ideal soil type for soybeans is
loam (Manitoba Agriculture, Food and Rural Initiatives 1). Although they do perform quite well
on heavier clay soils, challenges experienced with these soils include difficulty planting and
emergence problems. Drought conditions are often a concern when growing soybeans on
sandy soils.
When selecting a field to grow soybeans on, it is important to leave three years between the
same pulse crop, and two years between different pulse crops, as the same diseases can affect
them (Guide to Field Crop Protection 2012).
Variety selection
The first choice to make when selecting a soybean variety to grow is if you are going to go the
conventional or Roundup Ready route. Most soybeans grown are Roundup Ready varieties.
It is very important to select a soybean variety rated for your area. Each variety is assigned with
a company crop heat unit (CHU) rating (Seed Manitoba 2012). These ratings help growers
select varieties that have appropriate maturity dates for their areas. As CHU ratings are not
always exact, it is a good idea to use the ‘relative days to maturity +/- check’ column in the Seed
Manitoba guide as a second information source. The ‘relative days to maturity’ is determined
by the number of days from seeding to maturity for a variety from four common sites. A third
way to evaluate the maturity of a variety is to look at the season designation – long, mid or
short season. The short season label is usually applied to areas on the outer edges of current
soybean growing areas. Long season generally refers to the area of Manitoba south of highway
23, on the more central and eastern side of the province. The mid season reference applies to
areas between the short and long season areas.
Soybean varieties have differences in the colour of their hilum (where the seed attaches to the
pod) (Seed Manitoba 2012). The colours include yellow, imperfect yellow, grey, brown, buff
and black. The hilum colour has no agronomic effects, but can affect some export markets.
Some soybean varieties can be affected by Iron Deficiency Chlorosis (IDC). IDC is a disease
caused by a shortage of iron in the plant (Plant Health Initiative 2009). As iron is a necessary
component of chlorophyll, leaves become pale green, yellow or white, inhibiting growth and
reducing yields. IDC occurs in high pH soils where there is poor drainage and high levels of
soluble salts and lime. Seed Manitoba 2012 gives two indicators for IDC – a rating score and a
grouping. The rating score is a numerical value ranging from 1 to 5, with 1 being green leaves
and 5 being severe chlorosis and a stunted growing point. A lower rating score means the
variety will grow better on iron deficient soils. IDC groupings are split into three categories –
tolerant, semi tolerant and susceptible. Varieties with close numerical ratings can be in
different groupings, but still show similar symptoms. The same varieties can have different
visual rating scores in different years.
There are several different varieties that are suitable to be grown in western Manitoba. An
example of a few are Pekko (Brett Young), Libau (NorthStar Genetics), LS 003 (Legend Seeds)
and Anola (NorthStar Genetics).
Field preparation
As with any crop, starting with a clean field is essential to maximize your yield potential.
Soybeans are not strong competitors, therefore, it is important to get an effective burn-off
done. Glyphosate can be sprayed alone, or mixed with Express SG (Dupont product), Heat
(BASF product), or CleanStart (Nufarm product). In most situations, Heat looks to be the safest
and most effective of the three options. If the field is going to be worked in the fall or spring
before sowing soybeans, Edge (Dow AgroSciences product) is another early season weed
control option.
If Express SG is used, the rate is 80 acre/bottle (standard rate for all registered crops). Express
SG must be tank mixed with glyphosate (any glyphosate brand is okay). The Express SG is
added first, followed by the glyphosate when tank mixing Express SG and glyphosate. Before
using Express SG, it is important to know the soil characteristics of the field it is to be applied to.
To avoid crop injury, the soil organic matter must be greater than 3%, and the sand content
needs to be below 50%. Express SG should be applied a minimum of 24 hours before seeding.
Although Express SG is registered for soybeans, Express PRO is not.
If using Heat, only the 80 acre/bottle rate is safe. At rates higher than this, the soybeans may
experience tolerance issues. Similar to Express SG, Heat must be tank mixed with glyphosate
(any brand okay). Two jugs of Merge must be added to the spray tank for every 80 acre bottle
of Heat used. The tank mixing order is Heat, glyphosate, Merge. The ideal timing for Heat
application is just before crop emergence. This ensures that the maximum residual activity of
the Heat can be taken advantage of. When Heat is applied before seeding, the soil disturbance
in the seed row will move the residual Heat into the row spaces, resulting in weeds growing in
the seed row. At the 80 acre/bottle rate of Heat, 4 – 7 days of residual activity can be
expected, depending on conditions. At higher moisture/rainfall levels, the residual is less than
when lower rainfall amounts are received. Also, the length of residual activity is dependent on
soil texture, with shorter residual on sandier soil than on heavy clay soils.
Clean Start is a pre-packaged product of a ½ litre of glyphosate and Aim. The registered rate is
40 acre/case. The rate can be increased to 20 acre/case if the grower is targeting weeds that
more glyphosate alone would not help with, such as extreme pressures of or larger than
labelled Roundup Ready canola. If only a higher glyphosate rate is desired, Clean Start can be
topped up with an addition of glyphosate. It is recommended to not go over 1 litre REL/acre of
glyphosate (Nufarm). If using the 20 acre/case rate, no additional glyphosate can be added,
and at the 40 acre/case rate, only ½ litre REL can be added. If the 40 acre/case option is used,
the following glyphosates are compatible for tank mixing: all except for Touchdown and the
cheap Chinese glyphosates. It is important to use a minimum of 10 gal/ac of water to ensure
that the Aim component performs effectively. Clean Start must be applied before seeding, with
no waiting period between spraying and seeding.
Table 1 – Pre-seed/Pre-emergence glyphosate additives – options for use before a soybean crop (Guide to Field Crop
Protection 2012)
Product
Rate
Water Volume
Tank mix glyphosate
Express SG
80 ac / bottle
5 – 10 gal/ac
Any glyphosate okay
Surfactant required
None
Application timing
Minimum 24 hours
before seeding
OM > 3%
Sand content < 50%
No restrictions one
year after. Canola,
flax, lentils, alfalfa may
be planted 2 months
after application.
Soil restrictions
Re-cropping
restrictions
Mixing order
Heat
80 ac / bottle
5 - 10 gal/ac
Any glyphosate okay
CleanStart
20 - 40 ac/case
Min. 10 gal/ac
All except
Touchdown and
the cheap Chinese
glyphosates
2 jugs Merge per bottle None
of Heat
Just before emergence Before seeding
none
Canola, dry beans, flax,
mustard, all registered
crops may be seeded
year after use. Canola
may be planted the
spring following a fall
application.
Express SG, glyphosate Heat, glyphosate,
Merge
none
All crops may be
planted 12 months
after application
Aim, glyphosate
Edge is a granular grassy and broadleaf chemical that must be incorporated into the soil within
24 hours of application (Guide to Field Crop Protection 2012). A second incorporation, at a
right angle to the first, must be done at least three days after. If Edge is fall applied, both
incorporations should be done in the fall, however, the second incorporation can be left until
spring to conserve trash if it is done to the same depth as the first. The rate of Edge used is
dependent upon timing of application (fall or spring) and the soil texture and organic matter of
the field (details on page 135 of the Guide to Field Crop Protection 2012). There are several recropping restrictions with the use of Edge. The ones most relevant to our area are: i) oats and
small-seeded grasses (timothy, canary seed) cannot be grown after a crop treated with Edge
and ii) wheat cannot be seeded as a rotational crop onto land treated with Edge at the
oilseed/special crop/barley rates for two consecutive years.
Seed treatments and inoculants
Before soybeans can be planted, they need to be treated with double inoculant and a seed
treatment to help ward off disease and insects. It is recommended that soybeans in our area
receive double inoculant because the rhizobia needed to colonize soybean roots are a different
strain from peas, and is not found naturally in our soils (Brett Young Seeds). There are three
different forms of inoculants – peat, liquid and granular. Peat and liquid are both applied
directly to the seed, whereas granular inoculant goes down into the seed row (separately from
the seed) through an attachment to the air drill. It is also recommended to use two different
types of inoculant, a granular with either a liquid or peat, in order to maximize the number of
nodules present on the roots (Manitoba Agriculture, Food and Rural Initiatives 2). Because the
liquid and peat inoculants are placed on the seed, once the main root tip has grown away from
the seed, the rhizobia can no longer colonize that root, and the number of nodules cannot be
increased. The use of granular inoculant gives the opportunity for nodules to form on lateral
roots, as well as the main roots. Because granular inoculants are in the seed row, the lateral
roots can come into contact with rhizobia, and be colonized, giving a greater number of nodules
than if liquid or peat were the only inoculant types used. There are several different choices
when it comes to inoculants. The Isis soybeans this year will come treated with Cruiser Maxx
seed treatment and Optimizer, a liquid inoculant that has an extender in it to prolong the life of
the bacteria. It is also recommended to add TagTeam granular to the seed row. You may
observe that the leaves on the soybeans are a light green or pale yellow colour (Ontario
Ministry of Agriculture, Food and Rural Affairs 1). This often happens before the nodules are
fully functional, and is a normal phase of development that lasts about 7 – 10 days. Once the
nodules begin producing nitrogen, the leaves will become a dark green colour.
Soybean seeds are susceptible to seed and seedling rots (Manitoba Agriculture, Food and Rural
Initiatives 1). There are options when choosing a soybean seed treatment, but Cruiser Maxx
seed treatment has both a fungicide and an insecticide (Guide to Field Crop Protection 2012). It
has also been used extensively in eastern Manitoba, where it consistently shows a 5
bushel/acre yield increase (Brett Young Seeds).
Seeding
The recommended seeding rate for soybeans is 200,000 – 230,000 seeds/acre (Brett Young
Seeds). It is important to keep the seeding rate high when seeding soybeans with an air seeder
so that the plants compete somewhat with each other and grow taller, reducing harvest losses
from pods too low to the ground being left in the field. For the first few times growing
soybeans, growers should not alter the row spacing on their air seeders (Brett Young Seeds).
Once the grower becomes comfortable growing soybeans, some air seeder runs can be blocked
to increase row spacing and decrease seeding rates.
Under moist conditions and in a loamy or heavy soil, soybeans should be seeded ¾ to 1 inch
deep (Manitoba Agriculture, Food and Rural Initiatives 1; Grow Community of Independents). If
conditions are drier, or the soil is sandier, seed up to 1.5 inches deep to make sure the seeds
are into moisture.
Soybeans should be sown between May 15 and May 25, when the average soil temperature is
at least 10°C, although the ideal soil temperature for soybeans is 18 – 22°C (Manitoba
Agriculture, Food and Rural Initiatives 1).
Fertilizer
Soybeans do not require any nitrogen fertilizer, as long as effective nodulation occurs
(Manitoba Agriculture, Food and Rural Initiatives 1). Application of nitrogen fertilizer to
soybean can delay nodulation. If nodulation does not occur, and the leaves are yellowing at
early flower, nitrogen can be broadcast onto the crop.
The common phosphorus recommendation for soybeans is 30 to 40 lbs/acre (Manitoba
Agriculture, Food and Rural Initiatives 1). Sideband or 1 inch below the seed are common
placements for phosphorus. The maximum safe rate of phosphate applied with the seed is 10
lbs P2O5/acre for seed rows with a width of 15 inches or less (Soil Fertility Guide). If seed row
widths are greater than 15 inches, the safe rate of P2O5/acre is 0 lbs/acre. Phosphorus
deficiency symptoms are varied, and include stunted growth, dark green leaf colour, necrotic
leaf spots, purpling of the leaves and leaf cupping, as well as delayed blooming and maturity
(Kansas State Agronomy Update 2008).
Potash requirements for soybeans usually range from 30 to 60 lbs/acre (Manitoba Agriculture,
Food and Rural Initiatives 1). Due to seed sensitivity to potassium, the potash should be
applied away from the seed. Yellowing or browning on the leaf margins of the older leaves
indicates a potassium deficiency (Ontario Ministry of Agriculture, Food and Rural Affairs 2).
A common sulphur recommendation for soybeans is 20 lbs/acre of sulphate (Soil Fertility
Guide). Similar to potash, it should be placed away from the seed. Sulphur deficiencies in
soybean show up as stunted, pale green plants (Kansas State Agronomy Update 2008).
Rolling
The soybean field needs to be rolled after planting and before crop emergence. The purpose of
rolling is to conserve moisture and to level the field by pushing rocks into the soil, making it
easier to harvest the soybean crop. If rolling is done after the soybeans emerge, damage can be
done to the plants.
In – crop weed control
The type of in-crop weed control that is used depends on the variety selected. If conventional
soybeans were chosen, then there are several different options available to growers (Guide to
Field Crop Protection 2012). The choice of chemical in a conventional system will depend on
several factors, including the stage of the crop, weed spectrum of the field, tank-mix options,
re-cropping restrictions of the chemicals and the plans for next year’s crop, and the pre-harvest
interval of the chemical.
In Roundup Ready soybeans, glyphosate applications must be made after the plant has its first
trifoliate leaf through flowering (Guide to Field Crop Protection 2012). A single application of 1
litre REL may be applied for regular weed pressures, followed by a second 1 litre REL application
if late flushes of weeds are present. Alternatively, a single application of 2 litres REL can be
made if very heavy weed pressures are present at the timing of the first application. It is
important to check the label of the glyphosate product before applying it to Roundup Ready
soybeans, as not all glyphosates are registered for use. Recommended water volumes for
spraying glyphosate are 5 to 10 gal/acre. There are no re-cropping restrictions after spraying
glyphosate alone.
Disease
Manitoba soybean crops can be affected by three diseases – root rot (damping off), powdery
mildew and sclerotinia (Manitoba Agriculture, Food and Rural Initiatives 1). Root rot is caused
by soil-borne fungi that can attack any part of the root system and the portion of the stem at
the soil line (Manitoba Agriculture, Food and Rural Initiatives 3). Root rot usually leads to the
death of young seedlings. Symptoms of root rot are yellow colouration, stunted growth, with
brown-black lesions on stems and roots. In severely infected plants, the underground parts are
constricted, rotted and dark brown, leading to the loss of lower leaves and death of the plant.
In addition to the above symptoms, indications of a root rot infection in a field are patchy
stands, with missing plants in the rows. Prevention options include using seed treatments to
protect the seedlings. Use of seed treatments is especially recommended during cool, wet
springs. A second method of prevention is following a 5 year crop rotation to reduce the build
up of root rot fungi in the soil.
Figure 1 – Root rot. Picture on left caused by Fusarium species, picture on the right caused by Phytophthora (Ontario
Ministry of Agriculture, Food and Rural Affairs 4).
Powdery mildew is a disease caused by fungi that produce brown, pitted spots on the pods, and
the premature ripening may cause shrunken seed
(Manitoba Agriculture, Food and Rural Initiatives 4).
A light, greyish powdery growth on the leaves, pods
and sometimes on the stems are symptoms of
powdery mildew. This powdery growth can be
rubbed off, and over time, fruiting bodies develop
in the powdery growth. The fungi overwinter on
plant debris, and the inoculum is spread by wind.
Powdery mildew develops in lush crop stands, with
Figure 2 – Powdery mildew on soybeans. (Manitoba
dew formation and temperatures between 20 Agriculture, Food and Rural Initiatives 4)
25°C. Rain can help to disrupt the disease cycle. If
crops are planted early, they usually escape the
effects of this disease.
Sclerotinia is another fungal disease (Manitoba Agriculture, Food and Rural Initiatives 5), and
can cause large yield losses. In addition to reduced yields, affected seed can be discoloured and
light weight. The disease overwinters as sclerotia (hard black bodies) in debris from the
previous crop and in the soil. When temperatures reach 20 – 25°C, and there is adequate
moisture, the sclerotia germinate and produce tiny
mushroom shaped structures. The mushrooms
mature, and produce spores. These new spores
germinate and infect the growing crop, using the
plant’s own dropped flower blossoms as a source of
nutrients. Within 2 –3 days, the fungus can spread
from the dead blossoms of one plant to the adjacent
flowers, stems, leaves and pods. The sclerotia
formed during the growing season may stay in the
harvested crop or fall to the crop residue or soil.
Symptoms are present on the stems, leaves, pods
and even the seeds of soybeans. The first visible
symptoms are brown, water-soaked lesions, which
grow under cool, moist conditions, into watery,
rotted areas of plant tissue. The lesions then
become covered with white, cottony growth. Black
sclerotia are formed within the infected tissues,
usually in about a week. In the final stages, the
lesions become dry, bleached and shredded. The
branches and main stems of the infected plants may
wilt and die when the fungus circles the stem.
Increasing row spacing can improve the air flow
between plants, which may help to reduce the
occurrence of Sclerotinia. Crop rotation is an
important tool in managing sclerotinia, leaving 3-4
years between bean crops, as well as avoiding other
sclerotinia-susceptible crops in rotation will help
reduce the number of sclerotia present in the soil.
There are no registered in-crop fungicides for
control/suppression of sclerotinia in soybeans. However, there is Contans WG, a biological
fungicide (Guide to Crop Protection 2011). It is a relatively new product available on the
market, and it is sprayed onto the soil approximately 3 months before the onset of the disease.
It can be either spring or fall applied, and needs to be incorporated into the top 2 inches of the
soil after application. The rate of application is 0.4 to 0.8 kg/acre, with a water volume
sufficient to give thorough coverage of the soil or remaining crop residue. Contans WG infects
Figure 3 – Top: Mushroom-like structures (Manitoba
Agriculture, Food and Rural Initiatives 5); Middle:
cottony-white, bleached stem lesion; Botton: black
sclerotia bodies produced on/in stems and pods
(Ontario Ministry of Agriculture, Food and Rural
Affairs 5).
the sclerotia in the soil, preventing production of spores to infect the growing crop with. This
product cannot protect the crop from spores that blow into the field.
Insects
Soybeans are affected by several insects,
including soybean aphid, grasshoppers,
wireworms and cutworms. Soybean aphids
are pale yellow, and adults may or may not
have wings (Ontario Ministry of Agriculture,
Food and Rural Affairs 3). The eggs are laid
on twigs of the buckthorn species, nymphs
hatch in the spring, and the aphids go
through two, wingless adult generations on
the buckthorn plants. It is the third
Figure 4 – Soybean aphids (Ontario Ministry of Agriculture,
generation that causes problems in
Food and Rural Affairs 3).
soybeans, as these winged adults move
onto soybean plants. Once on the soybeans, the aphids produce wingless after wingless
generation, until overcrowding occurs, and resources become too limited. At this point, a
winged generation is produced, which moves to less crowded soybean plants. The aphids are
all female, until the fall when males are born to mate with females and produce the eggs on the
buckthorn plants. Over the spring and summer, all female aphids are born pregnant, and give
birth to live nymphs. As many as 18 generations can be produced per year on soybeans.
Aphids damage soybeans when they suck juices and nutrients from the plant using their
piercing-sucking mouthparts. Symptoms of threshold levels of aphids include aborted flowers,
stunted plants, reduced pod and seed quality. If the aphid infestation occurs when soybeans
are beginning to bloom, flowers are aborted. Infestation at this time causes the greatest yield
loss. Infestations during pod fill and later usually result in smaller seed size and lower seed
quality. Early in the growing season, aphids are found on emerging leaves and the upper
trifoliates. As the season progresses, the aphids move down the plant to avoid heat and
predators. Fields should be checked every 7 – 10 days (every 3-4 days when aphid numbers
approach threshold), and counts done on 20 -30 plants across the field, avoiding the field
edges. Scouting should continue until the crop has filled the upper pods, leaves begin to yellow
and lower canopy leaves begin to fall off. Once aphid counts reach 250 – 300 aphids/plant,
scout frequently to see if numbers increase (Guide to Crop Protection 2011). At 250 – 300
aphids/plants, they do not cause economic yield loss. If aphid numbers remain steady, there
are enough natural predators to keep the aphid population from reaching the economical
threshold. If aphid numbers are increasing during the time soybeans are beginning to bloom
and starting to set seed, treatment is economical. Treatment options include Cruiser Maxx
seed treatment (Syngenta product), Concept (Bayer product), Matador (Syngenta
product)/Silencer (MANA Canada product) or Lagon (UAP product)/Cygon 480 EC (IPCO
product).
Table 2 – Available insecticides for treatment of soybean aphids in soybean crops (Guide to Field Crop Protection 2012)
Product
Rate
Water volume
Concept
132 – 263 ml/ac
10 – 20 gal/ac
Application timing
When pest has
reached economic
threshold levels
Ground
Contact and systemic
Very toxic
20 days
Do not use after
group 4 seed
treatment (ex. Cruiser
Maxx bean)
Min 5 day interval
between applications
3
Application method
Contact/systemic
Toxicity to bees
Pre-harvest interval
Restrictions
Maximum # of
applications/year
Matador/Silencer
34 ml/ac
Not specified, but
need good coverage
(10 gal/ac min)
When pest has
reached economic
threshold levels
Ground, aerial
Contact and stomach
Very toxic
21 days
Min 7 day interval
between applications
Lagon/Cygon 480 EC
0.28-0.4 L/ac
Sufficient water for
good coverage (10
gal/ac min)
When pest has
reached economic
threshold levels
Ground, aerial
Systemic and contact
Very toxic
30 days
Wait 10 days before
putting leafcutter
bees in treated field
2 @ 33.2 ml/ac
Check label
Grasshoppers feed on the leaves and pods of soybeans (Manitoba Agriculture, Food and Rural
Initiatives 1). Grasshoppers lay eggs from late July into the fall (Manitoba Agriculture, Food and
Rural Initiatives 6). The eggs overwinter in the soil, and hatch from late April, early May until
mid-late June. Grasshopper eggs cannot start to hatch until the soil temperature has been 15 –
16°C for approximately 200 hours. It takes grasshopper nymphs 35 – 55 days to reach maturity,
and the adults live for 4 – 6 weeks. There is usually very little effect observed on yield if
moderate feeding occurs before flowering, as at this point, defoliation of 50% results in a yield
loss of only 3% (Manitoba Agriculture, Food and Rural Initiatives 1). However, if populations
reach 8 – 12 grasshoppers per square metre before flowering, control is often economical
(Manitoba Agriculture, Food and Rural Initiatives 6). Once the soybeans have begun to flower
and pod, the economic threshold for control is 2 grasshoppers per square metre. There are
several options that can be used to try to control grasshoppers. Hopper baits, which are an
insecticide on bran, are a low cost option that is not harmful to pollinators and other beneficial
insects. Hopper baits are usually applied with equipment that is used to spread granular
herbicides or seed. A common grasshopper control strategy is to spray the grasshopper
nymphs in the ditches and field headlands to keep them from moving into the rest of the field.
In severe cases, it may be necessary to treat the entire field. Matador (Syngenta
product)/Silencer (MANA Canada product) are the only insecticides registered for grasshopper
control in soybeans. The product and use information is the same as that in Table 2 for
soybean aphids.
Wireworms feed on germinating seeds and young seedlings, causing damage by shredding the
stems (Manitoba Agriculture, Food and Rural Initiatives 7). Adult wireworms are known as
‘click beetles’ because they are able to flip themselves upright when on their backs, and the
flipping action causes a click sound (Ontario Ministry of Agriculture, Food and Rural Affairs 6).
Wireworms spend most of their 6 year life
cycle as larvae. They over winter in the soil,
and come to the surface in the spring when
soil temperatures rise (Manitoba
Agriculture, Food and Rural Initiatives 7).
Female beetles lay 200 – 1400 eggs from
May to June, after emerging from the soil.
The larvae (wireworms) hatch, and start
feeding on the roots, seeds and germinating
seedlings of plants. Larvae that are fully
grown pupate in the soil during July, and do Figure 5 - Wireworm larvae (Ontario Ministry of Agriculture,
Food and Rural Affairs 6)
not re-emerge from the soil as adults until
the following spring. Indications of wireworm feeding are non-uniform or gaps in the stand
(Ontario Ministry of Agriculture, Food and Rural Affairs 6). Injured plants are stunted and
wilted. Wireworms are most prevalent on fields with low soil disturbances and sandier soils.
Scouting for wireworms needs to take place before planting. Bait balls are buried 2 – 3 inches
below the soil surface, and the bait ball should be checked for wireworms a few days before
sowing the crop. If there is 1 wireworm per bait ball (Ontario Ministry of Agriculture, Food and
Rural Affairs 6), the economic threshold has been reached. Soil can also be sieved to a depth of
6 inches over a 20 x 20 inch area. Using this method, the economic threshold is reached when
32 wireworms per square metre are found (Manitoba Agriculture, Food and Rural Initiatives 7).
The only practical suppression method is to use a seed treatment with an insecticide in it, such
as Cruiser Maxx. There are no control/suppression methods that can be used if a wireworm
infestation is discovered after the seed has been planted.
There are cutworms in most fields most years, but usually at populations too low to cause
significant damage to crops (Manitoba Agriculture, Food and Rural Initiatives 8). The redbacked
cutworm is the species that most often causes economic losses in Manitoba. Other species that
contribute to losses are the darksided cutworm and the dingy cutworm. The species of
cutworm present in the field is important, as some complete larval stages sooner than others
and some are more likely to clip to stems or just chew on leaves.
Table 3 – Characteristics of common species of cutworm of economic importance in Manitoba
Cutworm species
Appearance
Redbacked
- Two broad, dull-red
stripes down length
of back
- yellowish-brown
head
Darksided
-similar to redbacked
cutworm, except grey
coloured instead of
red
Feeding activity
-young larvae: small
holes and notches in
leaves
-older larvae: eat
stems, often severing
them
Eggs
-young larvae: feed
on leaves
-older larvae: cut
plants at ground level
Over-wintering stage
Eggs
Dingy
-thin light line down
middle of back
-broader diagonal
marks that look like
tire tracks or ‘V’s on
both sides of thin line
-4 equal sized black
dots on back surface
of each abdominal
segment
-leaf feeders
-rarely cut plants off
Partly grown larvae
Cutworm moths lay eggs in or on the soil. After hatching, the larvae feed on the host plants.
Cutworm larvae moult (shed their skin) between each of their six instar stages (the darksided
cutworm has seven instars). During moulting, larvae are a few centimetres below the soil
surface, and are inactive. If larvae are moulting, they will not have a greenish appearance to
their mid-gut. When they are ready to pupate, the larvae move deeper into the soil. The
moths exit the soil through the tunnel the larvae made. Evidence of cutworm feeding is
notched, wilted or cut-off plants. The rows will have missing plants, and bare patches in the
field may even be present. Cutworms can be found by looking in the soil (from just under the
surface to 3-4 inches deep) around the cut-off or injured plants. Small larvae have the greatest
potential for damage as they have the most growing and eating to do. If the larvae are close to
being fully grown, it may not be economic to use control methods. The length of time it takes
larvae to move into the pupae stage depends on the temperature and the cutworm species,
with cooler temperatures extending the larvae stage. There is no specific economic threshold
for cutworms in soybeans given for Manitoba, but the economic threshold in dry beans is 1 or
more cutworms per metre of row when the cutworms are still less than 2 centimetres long.
Insecticide applications made in the evening when cutworms are feeding are most effective. In
situations where the cutworms are restricted to a few patches of the field, it may be more cost
effective to treat only the infected areas rather
than the whole field. Matador (Syngenta
product)/Silencer (MANA Canada product) are
the only insecticides registered for control of
cutworm in soybeans (Guide to Crop Protection
2011). The product and use information is the
same as that given in Table 2.
Harvest
The best way to harvest soybeans is by straight cutting using a flex-head header. They need to
be cut quite low to the ground to get the lowest
pods, as the best beans are often in the pods
lower down on the plant (Manitoba Agriculture,
Food and Rural Initiatives 9). Careful setting of
the combine is also important to minimize seed
cracking and splitting and harvest losses. Keeping
knives sharp and the reel speed at approximately
25% faster than the ground speed will help to
minimize the harvest losses (North Dakota State
University Extension Service). The ideal moisture
content for soybeans to be harvested at is 14%,
although it can be done at 17-18% if air drying is
available. The moisture content needs to be
below 14% before they can be stored safely.
Soybeans are prone to seed damage and harvest
losses due to pod shattering if they are combined
at moistures below 12%. If moisture contents get Figure 6 – Top: Redbacked cutworm, Middle: Darksided
cutworm, Bottom: Dingy cutworm (Manitoba
to 12% or lower, combining during the morning
Agriculture, Food and Rural Initiatives 8)
and evenings can reduce losses and seed damage.
Conventional soybean varieties can be desiccated using glyphosate at a rate of 1 litre REL when
the crop has 30% moisture or less (Preharvest Staging Guide). At this moisture level, the stems
are green – brown, the pods are brown and dry, and 80-90% of leaf drop has occurred. If the
crop is going to be used for seed, it is not recommended to desiccate it, as the glyphosate can
damage the germination of the seeds.
Storage
As soybeans need to be at a moisture content of 13% or below, it may be necessary to use
aeration or even a grain dryer to bring the moisture content down to a level safe for long term
storage (Manitoba Agriculture, Food and Rural Initiatives 9). Aeration works best when the air
temperature is still warm. If soybean harvest occurs later in the fall, aeration may not be able
to dry the soybeans very much as the cooler fall air does not have much drying ability.
Soybeans at 18% moisture will keep over the winter, after freeze up. If this is necessary, the
aeration fan should be run every couple of weeks to cool any ‘hot spots’ that may exist. The
high moisture soybeans will still have to be dealt with in the spring. Grain dryers can be used
to reduce the moisture content of soybeans, but the process has to be monitored closely. The
temperatures can easily become too hot, and the air too dry, causing cracked seed coats and
split seeds. For soybeans that will be used for seed, the maximum temperature of the dryer
should be 38-49°C to prevent harming the germination of the seeds, whereas safe
temperatures for crush soybeans are 54-66°C as the seed integrity is less important.
Conclusion
Although the above paragraphs contain only a brief discussion of the soybean growing process,
we hope that they will serve as a guideline for your farm. We are always available to answer
any questions and to help you deal with any concerns that you may have.
References
Brett Young Seeds, Jeremy Jones. Regional Account Manager for SE Saskatchewan and SW
Manitoba.
Guide to Field Crop Protection 2012. Manitoba Agriculture, Food and Rural Initiatives.
Grow Community of Independents. Grow Academy Business Agronomy Manual.
Kansas State Agronomy Update. 2008. Kansas State Extension Agronomy e-Updates. E-Update
070808.pdf, from www.agronomy.ksu.edu Accessed March 29, 2011.
Manitoba Agriculture, Food and Rural Initiatives 1. Soybean – Production and Management.
http://www.gov.mb.ca/agriculture/crops/specialcrops/bih01s01.html Accessed March 28,
2011.
Manitoba Agriculture, Food and Rural Initiatives 2. Factors affecting plant survival from flooded
soil. http://www.gov.mb.ca/agriculture/crops/cropproduction/gaa01d51.html Accessed
March 28, 2011.
Manitoba Agriculture, Food and Rural Initiatives 3. Root Rot (Damping Off).
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Manitoba Agriculture, Food and Rural Initiatives 4. Powdery Mildew.
http://www.gov.mb.ca/agriculture/crops/diseases/fac23s00.html Accessed March 29, 2011.
Manitoba Agriculture, Food and Rural Initiatives 5. White Mould (Sclerotinia).
http://www.gov.mb.ca/agriculture/crops/diseases/fac04s00.html Accessed March 29, 2011.
Manitoba Agriculture, Food and Rural Initiatives 6. Grasshoppers.
http://www.gov.mb.ca/agriculture/crops/insects/fad10s00.html Accessed March 30, 2011.
Manitoba Agriculture, Food and Rural Initiatives 7. Wireworms.
http://www.gov.mb.ca/agriculture/crops/insects/fad28s00.html Accessed March 30, 2011.
Manitoba Agriculture, Food and Rural Initiatives 8. Cutworms in Field Crops.
http://www.gov.mb.ca/agriculture/crops/insects/fad06s00.html Accessed March 30, 2011.
Manitoba Agriculture, Food and Rural Initiatives 9. Harvesting Soybeans in Late Fall.
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2011.
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Development. http://www.omafra.gov.on.ca/english/crops/pub811/2planting.htm Accessed
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Crops: Soybean Insects and Pests.
http://www.omafra.gov.on.ca/english/crops/pub811/13soybean.htm#soybean Accessed
March 30, 2011.
Ontario Ministry of Agriculture, Food and Rural Affairs 4. 2009. Diseases of Field Crops:
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Accessed March 30, 2011.
Ontario Ministry of Agriculture, Food and Rural Affairs 5. 2009. Diseases of Field Crops: Edible
Bean Diseases. http://www.omafra.gov.on.ca/english/crops/pub811/14edible.htm#plate161
Accessed March 30, 2011.
Ontario Ministry of Agriculture, Food and Rural Affairs 6. 2009. Insects and Pests of Field
Crops: General Insects and Pests.
http://www.omafra.gov.on.ca/english/crops/pub811/13general.htm#wireworm Accessed
March 30, 2011.
Plant Health Initiative 2009. Iron Deficiency Chlorosis.
http://www.planthealth.info/idc_basics.htm Accessed March 28, 2011
Preharvest Staging Guide. Monsanto.
Seed Manitoba 2012. Variety Selection & Growers Source Guide. Manitoba Agriculture, Food
and Rural Initiatives, Manitoba Seed Growers’ Association, Manitoba Co-operator.
Soil Fertility Guide. Manitoba Agriculture, Food and Rural Initiatives. Online version
http://www.gov.mb.ca/agriculture/soilwater/nutrient/fbd02s00.html Accessed March 29,
2011.