Welcome!
October
5, 2012
FREEZE
Sorghum
and Sudangrass
Temperatures
in the upper 20s are forecast for much of the area this weekend, which may be the first
fall freeze for some. Most concerns with the first fall frost deal with managing sorghum
species including sudangrass. When these species are injured
with the frost, the plant tissue releases prussic acid for a few days, which can be toxic
to livestock. If plants are only partially killed, which is likely with a light frost, new
shoots may start to grow which have more concentrated levels of prussic acid. Livestock
should be removed immediately if a frost occurs and kept out for 5-6 days. If new shoots
develop, livestock should be removed until the shoots are the appropriate height to graze
(18-20 inches for sudangrass and 24-30 inches for sorghum-sudan), or until 5-6 days after a hard freeze which kills all shoots
completely. For more information on managing sorghum species in the fall, see Steve
Barnharts article at https://www.extension.iastate.edu/CropNews/2011/0912barnhart.htm.
Alfalfa
Because
of the concerns with sorghum species, there is the false believe that alfalfa also becomes
toxic with the first fall freeze. Alfalfa does not become toxic with the freezing
temperatures, but there is a slightly greater risk of bloat, so the standard bloat
prevention practices should be used (ie dont turn hungry
cattle out into an alfalfa field where they might gorge themselves on the lush alfalfa).
Because
of the shortage of hay this year there will be the temptation to try to get a last cutting
of alfalfa this fall. Alfalfa has been under a lot of stress with the drought, which makes
the fall rest period even more important this year. Temperatures in the upper 20s will not
stop alfalfa growth, with more growth likely in the next week to 10 days. Its best
to wait until after a killing freeze (mid 20s) or until about mid-October to try to take
another cutting of alfalfa to minimize the stress on the plants going into the winter.
DROUGHT
CORN
Root
& Stalk Lodging
Its
amazing that there are fields yielding 200 bu/A and more with the heat and drought we have seen this summer. There
are also fields yielding less than 50 bu/A
and everything in between. Harvest has been made more difficult by the lodging that
is common this year. Its important to look to see whether the lodging is stalk
lodging or root lodging. One thing that is causing some of the poor yields is severe
rootworm damage in some of the corn on corn. Some of the Bt genetics is not performing as well as in the past. Rootworm
damage is much more apparent this year with the moisture shortage. Growers need to
consider not only crop rotation, but Bt
genetics rotation to try to reduce the problem with corn rootworm resistance. See Aaron
Gasmans article for more information at https://www.extension.iastate.edu/CropNews/2012/0824gassmannhodgson.htm.
Ear
Rots & Aflatoxin
I
have not heard of widespread problems with ear rots and alfatoxin
in the past couple of weeks, but there are some problems showing up even in
good corn fields. Corn fields should continue to be checked for ear rot
problems and those fields targeted for harvest first. The sooner the corn is dried down in
the bin, the faster the mold growth and aflatoxin production
is stopped. Aflatoxin production is greatest when the grain is
18-20% moisture, so harvesting before it gets down to 20% would be best. However, be sure
to have the corn checked in the field by the insurance agent if you suspect a problem with
aflatoxin. Once its in
the bin its too late for insurance to get involved. Aspergillus
flavis is an olive green mold. Just because the mold is
present does not necessarily mean the toxin is present. For a photo of Aspergillus ear rot and additional information on this subject, go
to: https://www.extension.iastate.edu/CropNews/2012/0801robertson.htm.
ISU Extension has a publication that explains sampling, testing and interpretation for aflatoxin. Go to: https://www.extension.iastate.edu/sites/www.extension.iastate.edu/files/www/PM1800.pdf.
A recent article by Charles Hurburgh on alfatoxin
and grain storage can be found at https://www.extension.iastate.edu/CropNews/2012/0927hurburgh.htm.
SOYBEAN
Green
Stem Syndrome
Ive
been hearing that soybean yields are also quite variable, although yields in the 50s are
common. Spots in fields that may drown out in the wet years may be yielding 70+ this year.
One problem that is quite widespread is that stems are remaining green even when soybeans
are testing less than 10% moisture, which is resulting in a lot of shattering. This green
stem phenomenon tends to occur when the soybeans are under stress during pod fill, which
certainly would have been the case this year. Usually there is also a yield loss
associated with this, because it occurs when there are less pods and less beans to fill,
resulting in the plant having photosynthates left
over causing the stems to remain green even after the beans have filled completely
and are mature. Green stem syndrome can be induced in plants by removing half of the pods
at R6 (full seed size). The freeze this weekend may help some to dry the stems down, but its better not to wait for these stems to mature because of the
increased shatter risk. Fields can be harvested where stems are still green, although it
is more difficult, requiring more power and there may be increased problems with plugging.
To address combine issues for drought affected corn and soybean crops, see Mark
Hannas article at: https://www.extension.iastate.edu/CropNews/2012/0808hanna.htm.
There is some extensive information on the green stem syndrome at this Virginia Tech
website: http://pubs.ext.vt.edu/2912/2912-1430/2912-1430.html.
FOR
YOUR CALENDAR
Integrated
Crop Management Conference
November
28-29
Ames
Details
will be posted at: http://www.aep.iastate.edu/icm/homepage.html
Ag
Chemical Dealer Update
December
5
9:00
a.m. to 4:00 p.m.
Highlander
Clarion in Iowa City
Details
will be posted at http://www.aep.iastate.edu/
Crop
Advantage Series
January
30
Highlander
Clarion in Iowa City
Featuring
Craig Johnson, Meteorologist & Executive Director of Iowa Academy of Sciences
Details
will be posted at http://www.aep.iastate.edu/cas/homepage.html
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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