April 6, 2011
A good portion of SE Iowa received a quarter inch to an inch of rain on Sunday and with both the topsoil and subsoil filled to capacity, drought is not the primary concern at this time. Hopefully we'll see rainfall patterns a little closer to normal and not what we've experienced in the last few years. Soil temperatures are in the upper 30s and low 40s now. You can see the 4 soil temperature data across Iowa at http://extension.agron.iastate.edu/NPKnowledge/soiltemphistory.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.
Thistles in Pastures
Now is the time to be spraying biennial thistles, like musk thistle and bull thistle. They 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.
I am already getting calls on Canada thistle control. For 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.
Herbicide Resistant Weeds
I have seen glyphosate-resistant waterhemp and marestail in the area, and suspect that this problem is fairly widespread now. It may only be a patch or two in the field, but with one waterhemp plant capable of producing up to 5 million seeds, it doesn't take long for the trait to spread through-out the field. With generic glyphosate now close to free, it is tempting to rely on it for our weed control needs, but if it's use continues to be abused, it will eventually be worth what it is being sold for (worthless since it will no longer be effective on any weeds). If we are going to protect the usefulness of this amazing herbicide, it's important to take steps now, even it means paying more in the short-term. Consider using soil-applied herbicides, and tank mixing with other herbicides that can help to control these problem weeds. Ignite (Liberty) is another option now that both Liberty-link corn and soybeans are available.
Is Glyphosate Causing Problems with Soybean Diseases and Micro-nutrients?
The short answer is NO. For a longer answer see http://www.weeds.iastate.edu/mgmt/2011/glyphosateconcerns.htm.
FOR YOUR CALENDAR
Iowa Learning Farm Planter Clinic
Kirkwood Community College Equestrian Warm-up Center
1) GPS-Planting Technology
2) Planting With Conservation in Mind
3) Basic Planter Set-up
4) Converting From Conventional to No-Till Planting
Speakers will include Brad Buchanan, Crop-Tech; Mark Hanna and Jim Fawcett, ISU Extension.
SE IOWA RESEARCH FARM SPRING FIELD DAY &
SPECIAL SESSION FOR CCAs
Details will be posted soon.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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