CURRENT SEASON – 2008
Soybean
Dandruff?? – August 15, 2008
I’ve received a lot of calls about the small white flecks associated with soybean aphids (especially in heavily infested fields). Not the little ‘White Dwarf’ aphids, but the empty, white pieces of fluff on leaves and the ground. These are actually cast skins of aphids (can you imagine what a kid’s bedroom would look like if they molted when they grew? Eeewwww…) Anyway, when these are present in very high numbers it’s usually indicative of some large change in population – we sometimes see it prior to a big emigration event (they’ve molted and are leaving) or a big population growth response. It indicates many individuals of the population have undergone a molting to a next stage at roughly the same time.
Are we out of the woods for this critter yet?? Well, the data we have on yield loss is all related to plant stage and although this is somewhat tied to calendar date, there’s yearly variation. All of our trials from R4 and earlier indicate you very likely to see an economic return from applying at/above threshold (250/plant). In R5, we more frequently than not see an economic return when treating at/above threshold. At R6, we more frequently do not see an economic return when treating at/above threshold. I don’t think we’ve ever seen an economic return treating at R7.
This actually all makes sense. Depending on when they invade the field oybean aphids chronologically cause yield loss by:
a) stunting the plant, thereby decreasing nodes & pods
b) decreasing number of seeds/pod
c) decreasing size of seeds
At the end of the season, loss of seed size is where we lose yield (pod and seed numbers already have been set). So as long as there is yield to lose, soybean aphids can cause yield loss – calendar date is irrelevant.
Click on the images below for larger versions.
Soybean Aphids: Check Previously Treated Fields!! – Aug. 12, 2008.
With seasonal aphid movement underway and good environmental conditions for reproduction, it would be a mistake to assume fields treated earlier in the summer will remain aphid free for the remainder of the season. Some will, others won't. Simple as that. Soybean aphid populations are variable field-to-field, usually because of different immigration & colonization rates. And, although the inflights seem to be decreasing, aphids are still moving in and around the region. Add the impact of early spraying on natural enemies, good weather and the new, unprotected soybean growth that comes on after application and you've got a recipe for aphid population growth.
Not all the news is dark. Immigration flights seem to be lessening somewhat. Although they're still common, I'm finding fewer winged aphids in fields than last week. It also seems the lady beetle populations are increasing in untreated fields and in our control plots, hopefully these will continue to grow and contribute to late season aphid control. Still, in West Central and NW Minnesota, we have seen treatable aphid populations up to R5 (and R6 in some trials) regardless of calendar date, so it's probably not a good idea to ignore previously treated fields, especially those sprayed more than 2 weeks ago.
Soybean
Aphids are Here . . . but for How Long???? –
Aug. 05, 2008. Ian MacRae &
Phil Glogoza
There
have been heavy flights of soybean aphids over the past week, resulting in lots of winged
aphids being found in many fields in the region. Environmental conditions
are also pretty good for aphid reproduction and although numbers of natural
enemies seem to be increasing, soybean aphid populations in some fields may be
growing beyond what these predators and parasitoids (Figure 1 B & C)
can control.
Very large inflights have also been known to overwhelm predator numbers, bringing in more than can be chomped. The result of this immigration is that scouting for soybean aphids should continue! Fields that have already been treated are still at risk, perhaps even more so; early spraying can remove natural enemies such as predators and parasitoids that would ordinarily help contain colonizing aphids. Insecticides will remove these natural enemies, which facilitates aphid establishment. If it’s been more than 10-15 days since insecticide application, it’s also important to realize that residual control will be significantly diminished and all of the new plant material that has been added over that 10-14 day period is not protected! Consequently, large inflights of soybean aphids can still place even previously treated fields at risk! Don’t assume previously treated fields will remain aphid free for the remainder of the season, continue scouting!
On the positive side, in
Another thing to consider this time of year is that our own aphid populations may be developing wings and getting ready to go elsewhere. When finding winged aphids on soybean, how do you know you’re dealing with recent arrivals and not ones from that field that are developing wings? This is important, winged aphids are motivated to leave and found new colonies elsewhere; non-winged adult aphids are colony builders, exerting most of their energy in having offspring. Sometimes, an entire population will be programmed to become winged adults and leave. So, if you’ve got winged arrivals, your populations will likely increase, if you’ve got aphids in your fields developing wings, they’re getting ready to leave and the population in your field may decrease!
Using a hand lens, look at the smaller aphids on the leaves, if they appear to have squared off shoulders (looks like they have shoulder pads) then these aphid nymphs are going to develop into winged aphids (Figure 1A). If the younger aphids have shoulders that go straight back, they’re going to become adult non-winged aphids and continue to build the colony.
"It's always
something..." Sunflower Bud Moth – July 18, 2008.
As
usual, what started as a slow bug year has thrown me a spitball.
Sunflower bud moth has been reported from numerous locations in eastern ND and
western MN. What has been showing
up is black, granular material on the stalk or around the base of the
developing head – this is frass (bug poop), and
a sign that sunflower bud moth larvae are feeding. Historically, even
high populations of sunflower bud moth do not usually cause serious economic
loss. The exception is when they attack the head, preventing normal head
and seed development (which we've seen in some cases this year).
Unfortunately, there's little to be done about this particular insect problem,
mostly because of where it's located. Like sunflower midge, these insects
are inside the plant making it extremely difficult to get chemistry to them,
and even long residual chemistries might not be that effective as we don't have
good information on their developmental rate (i.e
when the adults will emerge, etc).
terminals of immature
sunflower and leaf axils. The newly hatched larvae them tunnel into the
plant, the entrance hole is surrounded by black frass. The larvae feed inside stems and
complete their development inside the plant. They return to a location near the entry
hole to pupate. Most of the current observed insects are older larvae
(and even pupae) in them, indicating the damage has already been done in these
cases. Generally, sunflower bud moth feeds in the backs of developing
heads in later planted sunflowers. This also is what we're mostly seeing,
which makes sense - even if they got in early, most
sunflowers in the region emerged later.
In the images, the small brown capsule is a pupa, from which an adult will eventually emerge. In the image on the left, you can see where a sunflower bud moth caterpillar has burrowed and fed upon the developing head – this is the situations which will result in yield loss. Click on the images for higher resolution pictures…
There are a couple of good websites with more info on sunflower bud moth:
From North Dakota State University
Grasshoppers –
Jumping onto the scene… - July 02, 2008
Several locations in
Grasshoppers don’t like to lay eggs in tilled soil, consequently, most of the agriculturally damaging species will lay eggs outside of tilled fields; meaning they attack the edges of fields first. The exception is in no-till systems where grasshoppers will lay eggs within the field. To scout for grasshoppers, walk the field (early in the season start along the field’s edge) and visualize a 1 ft2 area along your path. As you come to the 1 ft2 area, count the number of grasshoppers within it (this is usually best done by counting the number of grasshoppers that hop out of the area or are moving within it); sample 20 locations and calculate the average no. grasshoppers per ft2. Because thresholds are based on numbers per yd2 (see Table below), convert the average number of grasshopper per ft2 area by multiplying by 9. One ft2 samples are used because it would be too difficult to count the number of grasshoppers in a square yard when populations are very high.
Grasshopper Populations – Treat At/Above ‘Threatening’ Levels
|
Rating |
Nymphs per square yard |
Adults per square yard |
||
|
Margin |
Within Field |
Margin |
Within Field |
|
|
Light |
25-35 |
15-25 |
10-20 |
3-7 |
|
Threatening |
50-75 |
30-45 |
21-40 |
8-14 |
|
Severe |
100-150 |
60-90 |
41-80 |
15-28 |
|
Very Severe |
200+ |
120+ |
80+ |
29+ |
For lots more information on grasshoppers in Minnesota, see our grasshopper page here.
Soybean Aphid Surveys in NW MN – June
25, 2008
We
scouted several soybean fields in the area today and didn’t find 
much
more than yesterday – aphids can be found in very low numbers in certain
fields and the plants are still relatively young. The fields most likely to have aphids
right now are those in which they generally show up first (i.e. if you’ve
got a field that usually has early aphids, go take a peek!). Based on the stages we’re seeing,
it does look like we’re starting to get our 2nd generation of
nymphs but the populations are still pretty small….
First Soybean Aphids
of the Season – June 24, 2008
Very low levels of soybean aphid have
been reported from west Polk county (we found some yesterday in our plots at
the NWROC in Crookston).
Populations are very low so far.
Ardell Knudsvig,
field scout for MDA, reports finding aphids in several fields, aphids were on
less than 10% of plants with low numbers where they did occur. Most of the aphids we’re finding
in
This coincides with reports from SE
& SW MN that aphids are starting to be show up in fields there. They've been reported from Rosemont,
Becker, Morris and
So, bottom line, soybean aphids are showing up on schedule, they’re not widely distributed yet and where they are found, they’re only at low numbers. So they’re definitely NOT a problem yet. It's probably a good idea to check those fields traditionally at highest risk just for presence and serious scouting will likely start in most locations within the next couple of weeks.
Selected Past IPM Updates
August 3, 2006 -
Tank Mixing Insecticides & Fungicides in Sugarbeet
July 25, 2006 -
Two-Spotted Spider Mite Feeding Damage
July 19, 2006 -
Soybean Aphid regional Update
June
16, 2006 - Orange Wheat Blossom Midge
in Southern MN? Let’s Find Out!
May 30, 2006 -
Soybean Aphid Makes A VERY Early Arrival
May 19, 2006 -
Cutworms in Sugarbeet
June
16, 2006 - Orange Wheat Blossom Midge
in Southern MN? Let’s Find Out!
May 30, 2006 -
Soybean Aphid Makes A VERY Early Arrival
May 19, 2006 -
Cutworms in Sugarbeet
July 05, 2005 –
Armyworm Flight, Crookston
June 06, 2005 –
Soybean Aphids – they’re back
May 23, 2005 –
Cutworms in Sugarbeets
July 2003 - Leafminer in Sugarbeets
July 2002 -
Armyworms in Small Grains
July 2002 -
Grasshoppers in The Red River Valley
May 2002 - Cutworms
in Sugarbeets
Fall, 2001 - Soybean
Aphid in NW Minnesota
August, 2001 - Lygus in Sugarbeets
July/Aug, 2000 -
Armyworm Outbreak in RRV
Fall, 2000 - Soybean
Aphid, A New Insect Pest in Minnesota Soybeans
June 20, 1999 - Potato
Leafhopper, Grasshoppers, Cereal Insects
Sept 12, 1999 -
Impact of Aster Yellows on Canola May be Greater Than You Think
Aug 31, 1998 - Lygus in Sugarbeets
Publications Available for Download
Insects
Grasshoppers -
Minnesota Grasshopper
Management - 2002 with color graphics
Minnesota Grasshopper
Management Brochure with scouting and control information (available as a
PDF file designed to be a tri-fold brochure).
Scouting -
Scouting for Insects
in Wheat, Alfalfa, and Soybeans - a manual prepared for the
Early Season
Scouting for Soybean Aphids - A guide to scouting early season soybeans for
soybean aphid.