Steve Barnhart, Iowa State University, 2004: http://www.ipm.iastate.edu/ipm/icm/2004/5-10-2004/frostyalfalfa.html
Steve Barnhart, Iowa State University, 2005: http://www.ipm.iastate.edu/ipm/icm/2005/5-2-2005/alfalfa.html
have surpassed 250 Growing Degree Days (GDD) (base 48, from Jan. 1) which suggests that it
is time to scout for Alfalfa Weevil. In a normal spring, we would not reach this
point in northeast Iowa until May. The easiest way to scout for Alfalfa Weevil is to
start with a sweep net just to survey a field. If there are some alfalfa weevil in
the net, then follow the proper scouting procedure in http://www.extension.iastate.edu/CropNews/2012/0402hodgsonsisson.htm (in
the paragraph above Table 1) to determine if the economic threshold is reached.
Alfalfa Weevil problems in eastern Iowa have been few in recent years, but the warm
winter may have allowed for higher overwinter survival of the pest, and alfalfa harvest is
still a ways off. Alfalfa weevil quit feeding
at about 900 GDD Base 48. You can monitor GDD
Base 48 progress at http://www.extension.iastate.edu/Pages/eccrops/alfalfaweevil.html.
There do not appear to be widespread problems with winter-kill in alfalfa, but there will always be some winter-kill, especially on older stands, so stands should be evaluated. Dr. Barnhart, ISU Extension Forage Specialist, posted basic information on stand evaluation of alfalfa and other forages at: http://www.extension.iastate.edu/CropNews/2010/0318barnhart.htm. A publication that helps assess root health is available at: http://learningstore.uwex.edu/assets/pdfs/A3620.pdf This publication also provides the other option for stand evaluation called the Stem-Count Method. This is actually a better evaluation method then for plant counts, but you have to wait for stands to reach 6 to 10 inches in height for the assessment to be reliable. An ideal stand has 55 or more stems per square foot. Consider replacing stands that are less than 40 stems per square foot.
POTENTIAL FOR SMALL GRAINS DECLINES AFTER ABOUT APRIL 15
those who may not have their spring seeding of small grains done yet, potential yields
decline for both oats and wheat about 10% per week for each week planting is delayed after
April 15, and an additional 15% per week if planting is delayed beyond May 1. A nice fact
sheet on growing spring wheat in Iowa is at http://www.extension.iastate.edu/Publications/AG202.pdf.
FORAGES AND WATERWAYS
In general, try to complete seeding of cool season forage grasses and legumes before May 1 as seeding after May 1 increases the likelihood that seeds will germinate but less frequent rainfall will allow the soil to dry out before roots are deep enough to reach moist soil, killing the seedlings.
Rye Cover: Time to Kill It
those using winter rye as erosion control cover, not as a forage crop for harvest, its
time to kill it off. You dont want it to get too tall for a couple of reasons:
1) the more growth, the harder to kill, 2) the more growth, the more alleopathic
compounds produced that could interfere with the following corn crop yield. And we
could add a third possible reason. Not knowing if we will get normal rainfall in
April, killing off the winter rye earlier will conserve soil moisture. If you have
25 minutes, an excellent webinar on Managing a Winter Rye Cover Crop by Jeremy Singer is
available for viewing at: http://www.extension.iastate.edu/ilf/Webinars/
Its the third webinar below the 2011 ILF Webinar Archives
heading. The discussion of spring management on killing off the rye ahead of corn
planting is about half-way through the presentation. In addition to the webinar, Dr.
Singer has a publication on this subject at: http://www.extension.iastate.edu/Publications/PM1999.pdf
warm temperatures have produced a bumper crop of winter annual weeds, as well as
perennials, in some no-till fields. It probably makes more sense to take care of those
soon with some 2,4-D and/or Roundup, and come back later with the residual soil
herbicides. The larger weeds may take more than the pint/A rate of 2,4-D. Corn can be planted 14 days after a quart of 2,4-D
and soybeans can be planted 30 days after the quart rate of 2,4-D. For more information, see the article from Bob
Hartzler and Mike Owen at http://www.extension.iastate.edu/CropNews/2012/0326hartzlerown.htm.
Musk thistle and bull thistle are much easier to kill if they are sprayed when they are in the rosette stage, before they begin to bolt in the spring. Although 2,4-D and dicamba can do a good job of killing emerged thistles, products that have greater soil activity, such as Milestone (3-5 oz/A), Forefront (1.5-2.0 pt/A), and Grazon P&D (2-4 pt/A), usually provide superior control, partly because they will also control seedlings that emerge after application.
the most effective control of Canada thistle, it is best to wait until the thistles have a
chance to grow some and are about to put on buds, which is usually in late May or early
June. Canada thistles have extensive underground root systems. It is easy to kill the
above ground part of the plant, but much more difficult to kill the root system so they
will not be back the next year. Milestone, Forefront, and Grazon
usually give the most consistent control. Higher rates are needed than for biennial
thistle control. Crossbow is not a good product for Canada thistle control, but is very
effective on multiflora rose and other woody and broadleaf
weeds. A fact sheet based on Canada thistle trials conducted in Johnson and Keokuk
Counties is attached.
the soils being warm and the soils in generally good condition, it has been difficult for
many to not plant until the date allowed by crop insurance.
We need to remember that we had a freeze on May 9, 2010. Any March planted corn in 2012 would likely need to
be re-planted if we have a freeze in May of this year. Most of the corn that got frozen
two years ago still had the growing point below ground, so it did re-grow, but some found
out it did not completely recover from that stress and so yields were reduced. For more
discussion, see Roger Elmores article at http://www.extension.iastate.edu/CropNews/2012/0327elmore2.htm.
can track soil temperatures at http://extension.agron.iastate.edu/NPKnowledge/soiltemphistory.html.
You can track soil temperatures at http://extension.agron.iastate.edu/NPKnowledge/soiltemphistory.html.
FOR YOUR CALENDAR
ISU SE Research & Demonstration Farm 25th Anniversary Celebration Crawfordsville
A tentative agenda, which will be updated as details are finalized, is at http://www.extension.iastate.edu/Pages/eccrops/meetserc.html.
ISU NE Research & Demonstration Farm Spring Field Day Nashua
As details become available, they will be posted at http://www.extension.iastate.edu/Pages/eccrops/meetnerf.html.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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