Summary
Lygus bugs and banded sunflower moth
are at high levels in some sunflower fields. Those
growing or scouting confection sunflowers should be
monitoring levels of these insects. Aphids numbers
continue to be high in some cereal fields in the
southwest. Localized high levels of grasshoppers have
resulted in some control measures in the eastern region
of the province
Recent Insect Concerns and Observations
Banded Sunflower Moth and Lygus bugs in Sunflowers
High levels of banded sunflower moth and lygus bugs
are noticeable in some sunflower fields. Late bud and
early flowering stage are good times to monitor
sunflowers for these insects. Both of these insects can
be a concern in confection sunflowers because they can
lower the quality of the seeds. Information on scouting
techniques, economic thresholds, and control timing can
be found on the MAFRI website at:
Over the past few years, lygus bugs and banded
sunflower moth have been at levels of concern in many
sunflower fields in Manitoba. These are the 2 insects
most likely to be of concern again this year.
Populations of seed weevils in sunflowers have been very
low in most areas of Manitoba over the past few years.
Red sunflower seed weevil is another insect to look for
when scouting sunflower fields in the early bloom
stages.
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Adult stage of banded sunflower moth |
Soybean Defoliators
Some have been noticing holes appearing in the leaves
of soybean plants, and when they look hard enough are
finding quite active green caterpillars that loop when
they walk. These caterpillars are called green
cloverworms. They are also quite abundant in our alfalfa
at the University of Manitoba Farm near Carman. They
differ from other loopers that many farmers and
agronomists would be familiar with, such as alfalfa
looper and cabbage looper, by having an extra set of the
middle legs. All caterpillars have 3 sets of legs at the
front, and several sets of smaller and thicker legs
called prolegs at the back. In the alfalfa and cabbage
looper, they have 2 sets of prolegs near the middle of
the body, and 1 pair at the back. In the picture of the
green cloverworm below, you can see they have 3 sets of
prolegs in the middle, and 1 pair at the end. I find
this the easiest way to distinguish green cloverworm
from alfalfa looper and cabbage looper, for those who
wish to look closely enough. You will also notice that
these caterpillars do not like being disturbed and
squirm rapidly, much like a diamondback moth will, when
disturbed.
Currently, the levels of defoliation being
reported are not economical and would have
little effect on yield. But some agronomists are
keeping track of the defoliation to ensure
levels don’t get economical.
Under most conditions, moderate defoliation
early in the season has little effect on final
yield of soybeans. As plants reach the flowering
and pod filling stages, then defoliation poses a
greater threat to yield. Research indicates that
soybean plants can sustain a 35% leaf loss prior
to the pre-bloom period. From pod-set to
maturity, the plant can tolerate only a 20%
defoliation level. |
Green cloverworm on soybeans |
Aphids on Small Grains
Some of the later seeded small grain fields in the
southwest have had economical populations of aphids that
needed controlling. At this time of year the stage of
the cereal crops is another consideration. Once cereal
crops get to the soft dough stage, the aphids will have
less effect on yield of the crop. The generally
recommended economic threshold and staging of controls
for aphids in cereals 12-15 aphids per stem prior to
soft dough.
Grasshoppers
Some higher grasshopper populations have been noticed
and controls applied in the Red River Valley recently.
Most of the control reported has been along borders of
fields so far. Some dead grasshoppers clinging to plants
have also been reported recently from the Red River
Valley. These grasshoppers are infected with a fungus
which results in them dying perched like this.
Eventually the body of the grasshopper with break open,
and being high in the canopy spores spread a greater
distance, increasing the odds of more grasshoppers being
infected. The incidence of this infection is increased
with warm, humid conditions.
Surveys and Forecasts
Bertha Armyworm Trap Results: The monitoring period
for bertha armyworm adults is now wrapping up. At many
locations, this week will be the 6th week of data
collecting, and the number of moths caught has peaked
and counts in the traps are starting to get low. So
after counts are taken for this week, traps can be
removed.
An updated forecast map (shown below), the raw data,
and instructions for interpreting the data can be found
on the MAFRI website at:
This forecast indicates that potentially economical
populations of larvae could be found over much of the
western and central portions of the province. Egg masses
are now starting to hatch and some young larvae are
present, so from now until swathing, canola fields
should be monitored carefully for bertha armyworm
larvae.
It is important that each canola field be monitored
in areas of high or moderate risk. The traps indicate
what to expect regionally, not what to expect in
individual fields. So even fields with lower adult
counts could have economical larval populations in
regions with high risk. And populations can vary greatly
between fields within a region. So you can’t assume
based on levels of larvae in neighboring fields what a
specific field likely has. Larvae and feeding will
become more noticeable over the next couple of weeks. So
this is something to pay close attention to.
Insect Identification Quiz: Knowing your Miniature
Alligators
The following alligator-like insect larvae
can currently be found in many crops. These are all
predators of other insects. What are they?
Answer: The brown alligator-like larva is the larva
of a green lacewing. It is eating an aphid in this
photo.
Both the black alligator-like larvae are lady beetles.
Like the adults, the larvae also have subtle differences
in their appearance. The species shown here with orange
patches is a seven-spotted lady beetle larva, while the
black and white species shown here is a thirteen-spotted
lady beetle larva.
These are all beneficial insects and will not harm the
crops. Lady beetle larvae are very noticeable in some
crops right now. I do occasionally get calls from
individuals wondering what all the alligator-like things
are in their crop, and whether they should be spraying
them. The answer is no, be thankful they are present,
they could be helping prevent some real problems.
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