|
Integrated Pest Management Newsletters and Information
IPM Stuff
All the pestilence that's fit to print
Issue 5
July 22, 2009
Print
this newsletter using Acrobat Reader
Table of Contents:
If you receive these newsletters
as forwards and would like to be on the mailing list subscribe send
a request to Molly Werner. You
get what you pay for. This is a free newsletter.
Upcoming Events
Upcoming events
at the U of M SW Research and Outreach Center (SWROC)
Minnesota
Strip Till Expo - Held at the SWROC on Tuesday, August 11
Crop
Weather
Keep up to date on all the
crop weather details during the growing season at the SWROC's weather
page.
Crop conditions in SW MN are
now officially bi-polar. The southern part has received more than adequate
rainfall. Soybean root rots appear to be the main concern. On the other
hand, there are some areas with optimum moisture and the crop shows
it.
Other areas are desperately
in need of rain. In these areas aphids and/or spider mites are a bigger
concern.
Herbicides
It is definitely the year
for herbicide injury on both corn and soybeans. Carry over and post
emerge problems are all being observed. Please be careful out there.
Corn
Corn rootworm
The odd year phenomenon (higher
rootworm populations in odd numbered years) continues. Root lodging
is significant in some of the corn rootworm studies at the SWROC. Both
northern and western corn rootworm beetles are now present. Peak emergence
is a week or two away.
Based on the amount of recently
killed volunteer corn some rootworm survival has occurred in soybean
fields. Volunteer corn that is still alive will be attractive to late
season beetles for egg laying. There are some real volunteer corn messes
in soybeans this year - or maybe they are volunteer soybean messes in
corn. It is a little hard to tell in some cases.
Soybeans
Soybean aphid increases
are slower this year. Spider mite populations continue to be observed
in drier areas. The unseasonably cool weather has helped keep both pests
in check. We have now hit economic threshold for soybean aphid in a
few plots at the SWROC. They are not typical of production fields as
they are small areas of soybean surrounded by corn. Steve Commerford
reported aphids near threshold in isolated fields near the Minnesota
River. If economic threshold for soybean aphids are reached and spider
mites are a concern in the field, an insecticide containing chlorpyrifos
(e.,g. Lorsban 4E and others) or an insecticide containing bifenthrin
(e.g Hero, Tundra, Discipline and others) are advised. As a caveat,
there is no efficacy data for bifenthrin against two-spotted spider
mite in Minnesota. I involves some reading but it is important to pay
attention to insect rates and resistance management guidelines for spidermite
on pesticide labels. Many pyrethroid insecticides can flare spider mite
populations. Spraying early for either of these arthropods is not advised.
I have just returned from
a brief aphid scouting trip. I was attempting to determine the western
range of soybean aphid. If soybean aphid populations exist west of Kadoka,
SD the population must be discontinuous with a western population occurring
somewhere west of Sheridan, WY. Unfortunately soybean aphid populations
significantly north or south of the I-90 corridor will have to be determined
on a later trip. Unlike soybean aphid, the trout population was doing
well.
Coming to a soybean field
near you. A late soybean aphid production 7/16/09. Lamberton, MN.
Heavy stippling and webbing
from two-spotted spidermite (Greenhouse example). This much webbing
would not be seen in the field where only the undersides of leaves would
show webbing. The silken threads allow spider mites to move with wind.
Root rots
On the return from the aphid
scouting trip I noticed quite a few areas of drown out and root rot
along I-90 and Highway 60. Rhizoctonia is unusually prevalent
this year as is Phytophthora. Steve Sodeman, Corey Sinn
and Nick Pieske have called about Phytophthora problems. In Nick's
case the disease had overcome the Rps1k gene. Look for chocolate brown
lesions coming above the soil, wilting during the heat of the day, and
a shepherd's crook at the top of wilted, dying plants as symptoms of
Phytophthora this time of year. As mentioned in an earlier newsletter,
wet conditions favor fungal and bacterial diseases.
Leaf disease
Low amounts of downy mildew
(in wetter areas) and Septoria are present. Bacterial blight
lesions have started to form on upper leaves at the SWROC in spite of
dry conditions. Sunscald/Sunburn 2009 environmental conditions have
favored this abiotic problem in soybeans. Sun scald symptoms are most
common on lower leaf surfaces although symptoms can occur on the upper
leaf surface and pods as well. Lower leaf symptoms are rust to purple
cast to the leaf. Lower leaf symptoms occur when a leaf is flipped upside
down. Often, a portion of the leaf that has been covered by foliage
above it shows no symptoms. Upper leaf symptoms are similar and may
show areas of necrotic (dead) tissue. From a quick look at the popular
literature, the symptoms are most pronounced when bright sunshine and
low humidity are followed by a period of high humidity and cloudy weather.
High intensity sunlight through dew or other moisture droplets can also
produce symptoms. Look at the position of affected leaves in the canopy
and look back to the weather conditions when they would have been near
the top of the canopy. Expect no loss of leaves or yield from this phenomenon.
Soybeans have spare leaves, well above that needed for optimum yield.
Sunscald symptoms on the upper
leaf surface can be confused with disease, particularly Cercospora
leaf blight. Cercospora leaf blight (purple seed stain in pod and seed
infections) is caused by the fungus Cercospora kikuchii. Infection
and disease development is favored by warm temperatures (above 80 F)
and high and humidity. Foliar symptoms usually occur late in the season
during pod fill. See the University
of Minnesota Extension MN Crop Diseases website for more information
about this disease.
Sunscald might also be confused
with Frogeye
leafspot (Cercospora sojina) but symptoms are quite different.
While many of you have called
and emailed trying to provide good advice to growers, there are, unfortunately,
folks out there willing to turn soybean sunburn into a marketing opportunity.
I have not looked at every field, nor will I. There may indeed be some
Cercospora out there but I have a hunch that P.T Barnum is chuckling
in his grave.
Sunburn or sunscald on
lower (upper right) and upper soybean leaves.
Cercospora leaf blight
symptoms on soybean foliage. Note leathery appearance of leaf.
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
|
