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Integrated Pest Management Newsletters and Information
IPM Stuff
All the pestilence that's fit to print
Issue 7
August 31, 2009
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Table of Contents:
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Upcoming Events
Upcoming events
at the U of M SW Research and Outreach Center (SWROC)
The Southwest
Research and Outreach Center turns 50!
The Southwest Research
and Outreach Center invites you to celebrate with us 50 years of contributions
to southwest Minnesota. The celebration will occur from 2:00 - 5:00
pm on Sunday, September 13, 2009 at the Southwest Research and Outreach
Center, Lamberton, MN. A brief program at 3:00 pm will include comments
by Wally Nelson, Founding Head and Pauline Nickel, Current Head. Displays
will highlight activities through the decades as well as current work
in progress.
Other U of M Events
Soybean Plot Tour, September
10, Sibley County
Soybean Research Plot
Tour, September 15 by Westbrook, 2:00 - 4:00.
Arm yourself
with the latest University of MN research and information when selecting
soybean varieties and technologies by attending the U of MN Soybean
Research Plot Tour by Westbrook on September 15th from 2:00 to 4:00
pm. Compare the latest technologies and traits in the field while discussing
management strategies to optimize soybean profitability. The field day,
sponsored by U of MN Extension, the Murray County Corn and Soybean Growers
Association, Elizabeth Johnson, and Bob Nelsen, is free and open to
all who wish to attend and will be held rain or shine.
Jim Orf, U of MN Soybean
Plant Breeder, will discuss the latest soybean variety technologies
and traits as well as how Soybean Cyst Nematode (SCN) resistant varieties
differ in their ability to keep SCN populations down. Liz Stahl, Extension
Educator in Crops, will discuss trials being conducted across southern
MN where sources of SCN resistance are being evaluated. Bruce Potter,
IPM Specialist at the Southwest Research and Outreach Center, will discuss
SCN population shifts observed in Minnesota fields and address current
insect pest management issues in soybean.
Directions to the plot:
From Westbrook, go west on MN-30 for 3.2 miles. At the Rolling Hills
Golf Club, go south on 280th Ave/CR-67 for about 2 miles. The plot will
be on the west side of the road. In case of rain, the tour will be held
at the Bob Nelsen farmsite, just ¼ mile north of the plot (1173 280th
Ave.).
Liz
Stahl Extension Educator - Crops
Worthington Regional
Office
Crop
Weather
Keep up to date on all the
crop weather details during the growing season at the SWROC's weather
page. We could use a bit of heat and will need quite a bit of moisture
recharge in many fields.
Corn
Will corn mature in time?
Even with cool weather, figure 60 days from tassel until black layer.
Unless there is a very early frost most fields should be ok. Cool weather
with adequate moisture will help fill. Some heat wouldn't hurt though.
As Corn reaches the dough stage much of the yield is fixed and completed
at black layer. Corn is still quite wet (30-35%) at black layer.
Aphid and spider mites
have collapsed in many, if not all SW MN Corn fields. Hmmm… Fungal disease
seems to have been the main driver but emigration of winged Bird-cherry
oat aphids also occurred. Damage from these species is for the most
part minor and superficial and is shown in the photos above.
Damage from another species
can be more significant. Greenbug, Shizaphis graminum, saliva contains
compounds that are toxic to plants. This aphid species migrates into
Minnesota from the south and has been fairly rare at the SWROC over
the past few years. I have not seen any significant greenbug populations
on corn but we did have a few plots of sorghum at the SWROC that had
high greenbug populations. The red discoloration is a result of greenbug
feeding. In the right photo you might be able to see the distinctive
dark stripe on the body of the lower greenbugs. The upper aphid is diseased.
 Corn
rootworm
We are now finally past the
peak for Northern corn rootworm (NCR) emergence and beetle activity
in corn.
Damage from larval feeding
on roots is greater in 2009 than during 2008.
NCR beetles have begun foraging
heavily in soybean over the past couple weeks.
From on-going research it
appears that NCR lay eggs in soybean at very low levels, if at all.
On the other hand, egg- laying in soils around volunteer corn appears
to occur quite often.
Late season corn diseases.
Eyespot has been the
most commonly observed leaf disease on corn this season. It is more
pronounced on some hybrids and more severe in corn on corn fields. Common
corn rust is also becoming more visible, particularly on field edges.
Again, some hybrids appear more susceptible to this pathogen. With relatively
late onset, yield loss from these two diseases is likely to be minimal
in most, if not all, cases. At this point, pathogens that are more commonly
associated with yield loss such as Northern corn leaf blight, Anthracnose
(foliar) and Gray leaf spot, although present, are not prevalent
in most fields. The stalk rot phase of Anthracnose is showing up at
low levels in some fields.
On the left, Common corn rust-
Note the raised pustules. Similar to small grain and soybean rusts,
this fungus does not overwinter in Minnesota. On the right, Eyespot
lesions are often concentrated near the edges of corn leaves. Eyespot
overwinters on corn residue.
Stalk rots from several species
of fungi are now the primary concern from a management standpoint. Harvest
poor standing fields early when possible.
Soybeans
Most fields are at late R5
(beginning seed) to early R6 stage (seed filling cavity in pod at one
of the top 4 nodes). As the R6 stage progresses, insect, disease, and
environmental factors will have less effect on yield. In spite of the
cool weather, soybeans are maturing more or less on schedule. Areas
that were drought or spider mite stressed are maturing early.
Soybean aphid
 The
season is winding down for the 2009 soybean crop and soybean aphid (SBA).
Fungal disease and predators have slowed aphid increases in many fields.
The recent cool weather and persistent dews are conducive to entomopathogenic
(insect killing) fungi. The cold nights that parts of Minnesota are
experiencing may trigger a movement to buckthorn.
The image on the left shows
late season aphid colony. The dark colored aphids (bottom center and
scattered on leaf) are parasitized by fungi. Disease epidemics can quickly
collapse aphid populations.
Only late planted or very
full season soybeans are at risk from aphid losses now. As we reach
the early R6 stage soybeans can probably tolerate much higher populations
of aphids/plant. Yield loss can still occur in early R6 with high prolonged
aphid populations. Good growing conditions will allow soybeans to tolerate
higher SBA populations. At R 6.5 (a yellow pod on plant), very little
yield can be affected by insects and disease. SBA that have not reached
the 250 aphid/plant threshold by the end of the R5 stage are not likely
to accumulate enough aphid-days to affect yield in R6. Remember, 4000-6000
cumulative aphid days are required to cause yield loss during the earlier,
more sensitive pod initiation and formation stages.
I believe most of the decisions
for aphids were completed the last two weeks. If, however, you are questioning
whether you should still treat a soybean field for soybean aphids considers
the following:
- Do not treat SBA if portions of the field have started to turn
- Do not treat SBA if other problems in the field are more important
than aphids (SCN, mite damage, hail damage, etc).
- Do not treat SBA if aphid populations are not rapidly increasing.
- Do you see adults and nymphs both and an actively reproducing
population?
- Are there a high percentage of winged aphids or nymphs with
wing pads indicating emigration?
- Are predators or disease abundant?
- When late in the R5 to very early R6 stage estimate the amount
of time until R 6.5
- Do not treat SBA if pre-harvest intervals for insecticide are
an issue?
- Estimate what the population will be by doubling the current
SBA population every 3-5 days. Can you accumulate over 4,000 to
6,000 aphid days? This is going to be very conservative and err
on the side of treating. Do not treat SBA if soybeans will mature
before aphid populations can hurt yield.
Late season diseases
While Brown stem rot foliar symptoms are just beginning to become
obvious in many fields, the stem discoloration can be seen by splitting
stems at this time. This is probably the most under managed (ignored)
soybean disease in Minnesota. Pod and stem blight and Anthracnose
fruiting structures are starting to appear on senescing (dying) stem
tissue.
Top die-back is showing up in many SW MN soybean fields. The
fungus Diaporthae (Phomopsis is the asexual stage) can usually be cultured
from affected plants. In fact, these fungi can be isolated from most
soybeans late in the season. The nature of this soybean affliction is
not well understood. Symptoms range from yellowing of the upper leaves
to symptoms resembling potassium deficiency on upper leaves. The latter
symptoms can occur in soils testing low to medium for potassium and
may have a different pathology.
Diaporthae is the fungal genus that causes the stem diseases
pod and stem blight and stem canker. I do not know if
top die-back has been identified as one of these species. The amount
of yield loss associated with the fungal component of this disease is
unclear. Look for pod and stem blight fruiting structures in fields
that turn with an orange cast to them.
In the image on the left, top die-back begins as a yellowing of leaves
on the upper nodes of soybean. This is not maturity. The image on the
right shows K deficiency symptoms. These are fairly common symptoms
for SCN late in the season. Soybean aphid can cause a similar but distinct
symptom.
There are reports of symptoms occurring in the absence of Soybean Cyst
Nematode (SCN) but I have always observed it during late R5, after a
rainfall event and in association with at least a few SCN. It is also
possible these symptoms are all a reaction to SCN stress or have multiple
stress causes. It might be worth your while to check for SCN on your
roots where you see these symptoms in your soybean field. Sudden death
syndrome (SDS) is another disease that is associated with SCN.
Dean has also put together an article on late
season soybean disease.
 If
it seems that the topic of SCN is a recurring theme, it is. Many fields
I drive by show uneven growth, uneven maturity, poor row closure and
top-dieback. SCN may be a component in some or all of these, even where
resistant varieties are grown. For most producers, SCN is at the same
time over managed and under managed. In other words, SCN resistant varieties
are used in nearly all fields while at the same time little thought
is given to SCN populations or type of resistance used in individual
fields. This is giving SCN a wonderful opportunity to adapt to producers
management.
Jodie Getting (above) looking at SCN cysts on a resistant variety at
the SWROC. Note the SCN symptoms behind him. Jodie is proof that weed
guys are adaptable and trained to understand population biology and
genetics.
Syrphid flies.
 These
flies (Diptera:Syrphidae) are extremely abundant this year. The active
adult Syrphid flies are also known as hover or flower flies. Several
species occur in southern Minnesota. The high syrphid populations are
most likely the result of an abundance of aphids on many plant species
the past two years. Syrphid larvae feed on aphids.
These flies can be annoying and often land on people. The yellow and
black colors of the fly resemble a bee or wasp and are an example of
Batesian mimicry for defense. The flies are harmless and feed on nectar
and aphid honeydew.
Before you swat one, remember they are on our side in the battle with
aphids. If you are not much of a team player, be advised to check before
you swat. After all, there are still some bees and wasps left out there.
Herbicide
resistant weeds
If you have a field that has
a glyphosate tolerant weed problem, let me know. We are working with
a project in NW Minnesota and NDSU and would like to collect seed collection.
I will email instructions for determining whether the weeds are a candidate
for the project and instruction for collecting.
Reflections
on an almost finished growing season
At this point, there is little
that can be done for the current crop in terms of pest management. On
the other hand, it is important to note where problems have occurred.
Now is a good time to gather this information. Should you use a Brown
stem rot resistant variety next time the field is in soybean? Are nematodes
doing better on your cyst variety than you would like? How heavy were
the corn rootworm beetle populations in the field? Did you have stand
problems due to disease? These types of information are valuable in
designing effective long term pest management strategies.
When implementing crop pest
management strategies, it is not whether you will win the war that is
important. How long you can keep up the battle determines success.
As I reflect upon the season,
I am struck by how hardy our modern cultivars are and how many pest
management tools we have. The biggest challenge will be to preserve
valuable traits and chemistry. From my perspective, proper identification
of pests, an improved understanding of how yield happens and when economic
loss occurs is fundamental for long term profitability of Minnesota
crop producers.
I would like to thank the
Minnesota Soybean Research and Promotion Council, Minnesota Corn Research
and Promotion council and others for much needed financial support for
research. The field crew at the SWROC has been extremely helpful. 2009
student workers; Clay "The Boss" Churchill, Shayne "Little big wind"
Nipperman, Joe "Is it lunch time yet" Doubler, and Kaycee "You didn't
give me a growth stage" Altermatt ; worked extremely hard at some unpleasant
and boring tasks, including keeping me focused, They definitely kept
me on my toes and the summer entertaining.
Searching
for SDS (Sudden Death Syndrome) in SW MN Fields and NEW SDS Fact Sheet:
Conditions are right in some
fields this year for significant SDS to develop and reports of this
occurring have come in from a few areas of the state already. Dean Malvick,
Extension Plant Pathologist with the U of MN, is trying to determine
how widespread SDS is in MN. To date, he has had few confirmed reports
from SW MN and is particularly interested in receiving suspect samples
from our area.
If you suspect SDS in your
field or a field you work with, please send a sample to Dr. Malvick
at 495 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108-6024.
Samples should not be dried out and not in transit any longer than
necessary. Whole, fresh plants with roots, stems, and leaves should
be sent. Samples suspected to be SDS that are sent directly to Dean
will be diagnosed free of charge, thanks to funding from the Minnesota
Soybean Research and Promotion Council.
For more information, read
the fact
sheet covering the basics of SDS, including photos to help in the
diagnosis of the disease. Further information about soybean diseases
of MN can also be found at the Soybean
Diseases website.
Liz
Stahl Extension Educator - Crops
Worthington Regional
Office
REVISED
Soybean Cyst Nematode (SCN) Publication:
While preparing for a field
day, I ran across the revamped "SCN Management Guide" by the North Central
Soybean Research Program, Plant Health Initiative (funded through checkoff
dollars). The revised guide contains good background information SCN,
how to sample for SCN, a good explanation of HG Typing, and management
information. The 5th
edition of this guide is available online. You can also order
a copy.
SCN continues to be the most
destructive pathogen of soybean in North America, with more yield lost
to SCN than any other soybean pathogen. After years of planting resistant
varieties in SW MN, U of MN research is finding populations of SCN have
shifted in some MN fields and that not all "resistant" varieties are
created alike! Check out the plot stour announcement below for more
information.
Liz
Stahl Extension Educator - Crops
Worthington Regional
Office
This is the last issue for
the growing season unless some late season disaster occurs. There will
be periodic releases of research results and etc. during the late fall.
Until then, have a safe, productive and profitable fall.
Until next time,
Bruce Potter
IPM Specialist SW Minnesota
University of Minnesota
Extension
Department of Entomology
University
of Minnesota Southwest Research
and Outreach Center
23669 130th Street
Lamberton,
MN 56152
Ph:
507.752.5066
Fax: 507.752.5097
E-mail: bpotter@umn.edu
http://swroc.cfans.umn.edu/SWMNPEST/swmnpest.htm
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