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East-Central and Southeast Iowa Crop Information

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SOIL TEMPERATURES

April 12, 2005

SOIL TEMPERATURES

Soil temperatures have been in the 50's and lower 60's in recent days.  They will undoubtedly cool slightly in the next few days but will then warm up again.  Soil temperature information around the state can be found at: http://mesonet.agron.iastate.edu/agclimate/display.php?src=/agclimate/daily_pics/4in-temp-out.png.

PLANT OATS ASAP

Oats are a cool season crop and yield best when planted in late March to April 15 so that flowering occurs before the hot part of the summer. Grain yields drop about 10-15% per week after April 15 in the central part of the state.  So any oats yet to be seeded should be done as soon as soil conditions permit.  Seeding rate should be about 30 seeds per square foot, which is about 2-3 bu/A. Best results are obtained with a drill. See Small Grain Production for Iowa-Spring (Pm-1497) at http://www.extension.iastate.edu/Publications/PM1497.pdf.

Much of the oats seeding will be done as a companion crop for alfalfa and other small seeded forages. The seeding rate should be cut some to reduce competition with the forage. One to 2 bu/A of oats is commonly seeded with alfalfa.

FORAGE SEEDING

Forages may also be seeded by April 15, but mid-April to late-April is a better seeding time for forages since they require soil temperatures similar to corn and soybean for germination.

It is best to have forages seeded by late-April because as we get later into the spring, the soil surface tends to dry out more rapidly with the warmer temperatures, making successful establishment of forages more difficult. Seeding depth and seed-soil contact are critical for the establishment of alfalfa, smooth bromegrass, and other small-seeded forages. They should be seeded no deeper than 0.25-0.5 inches deep. Seed-soil contact can be improved by following the seeding with a cultipacker or harrow.

ALFALFA

Stand Evaluations

Although it seems likely that there are not widespread problems with winterkill, every year there are some fields with enough stand loss to justify re-seeding. It's time to start looking at alfalfa winter survival.  Stands can be estimated by either counting plants (crowns) or counting stems.

Plant Counts
The basic procedure to assess alfalfa stands has been through plant counts. Commonly recommended plant counts per square foot for a pure alfalfa stand are: > 20 plants in fall for the seeding year, > 12 plants in spring for the 1st production year, > 8 plants in spring for the 2nd production year, and > 5 plants in spring for the 3rd production year. Frankly, the plant count method seems to works fine for young stands (new seedings to 1 year old stands), but it does not correlate very well with older stands.

Stem Counts
A better method to evaluate alfalfa stands is the use the stem count method. However, this method requires alfalfa top growth to average at least 6 inches tall before the method can be used. Count stems per square foot in 4 to 6 representative areas in the field. Use the following table to estimate the yield potential of the stand. The yield potential is in context of realistic yields normally expected from that field. Actual yields can be less depending on problems with precipitation, insects, diseases, soil fertility, and harvest losses.

Table 1. Alfalfa stem counts and corresponding estimated yield potential.

Stem counts per square foot:

>54

50

45

40

35

30

25

Percent yield potential:

100

90

81

72

62

53

44


Table 2. Recommendations based on the stem count method.

Stems/sq.ft.

Recommendation

  >54

Not yield limiting.

  40-54

Usually keep. Some yield reduction.

  <40

Consider replacing. Significant yield reduction. May still keep it if significant grass forage is present.


Keeping the stand is an individual decision dependant on many factors, including: hay supply, available land, cash flow, etc. Table 2 provides general recommendations on whether or not to keep a stand. However, these recommendations are for pure alfalfa stands. Alfalfa-grass mixtures have a grass component that contributes to yield. If the desired stand was a 75:25 alfalfa:grass ratio, and assessment of alfalfa stem counts is about 41 stems per square foot (about 75% of a full stand), then the overall stand should provide 100% yield potential because the grass component makes up the other 25%.

Autotoxicity

Alfalfa produces compounds that inhibit the growth of other alfalfa plants. If an old alfalfa stand is rotated back into alfalfa, there is significant potential for the growth of the new seedlings to be inhibited by these compounds produced by the older plants. Recent research from the University of Wisconsin demonstrated that when seeding alfalfa into a recently killed current stand (plowed or herbicide application), the new alfalfa usually germinates, emerges, and survives, but yields tend to only be about 75% of normal. Basic recommendations are to rotate out of alfalfa for at least one year. If you must maintain a forage stand by seeding into a current stand, and you can't interseed some other forage (red clover, ryegrass), then it is probably best to plow down the old stand, wait at least 3 weeks, then seed the new stand. Even so, you can expect about a 10 to 30% yield reduction from the life of this stand compared to a rotated stand.  If you are interested, there is a summary of some of the research at: http://www.uwex.edu/ces/forage/pubs/autotoxicity_files/frame.htm.

Alfalfa Weevil

It is also time to start scouting hay fields for alfalfa weevils in areas along and south of Interstate 80 and very soon north of Interstate 80.  Alfalfa weevils begin to hatch at 300 Growing Degree days (GDD) Base 48 and quit feeding at 900 GDD Base 48. Because south facing slopes are somewhat warmer than average, they should be scouted beginning at 200 (south of I-80) - 250 (north of I-80) GDD Base 48.

Following are GDD Base 48 accumulations as of the end of the respective day.

DATE

BURLINGTON

CEDAR RAPIDS

DAVENPORT

DUBUQUE

April  5

179

134

146

102

April  6

196

151

164

119

April  7

204

158

172

127

April  8

215

169

183

137

April  9

229

182

197

148

April 10

251

202

216

166

April 11

267

217

232

182


For details on managing this insect, see pages 22-23 of the April 19, 2004 Integrated Crop Management Newsletter http://www.ipm.iastate.edu/ipm/icm/2004/4-19-2004/. Also, watch http://www.extension.iastate.edu/Pages/eccrops/insect.html for updated information on the development of this and other insects during 2005.

STALK BORERS BEGIN TO HATCH SOON

Assuming normal temperatures for the next few days, stalk borers will begin to hatch along Highway 34 (Burlington - Mount Pleasant area) on April 21, and the hatch will move north.  In areas of fields with high grassy weed or giant ragweed pressure in 2004, burning the residue or spraying an insecticide just prior to egg hatch are two strategies to consider if corn will be planted this year.  Stalk borers begin to hatch at 575 Growing degree days base 41 and hatch is complete at 750 GDD Base 41.

Following are GDD Base 41 accumulations as of the end of the respective day.

DATE

BURLINGTON

CEDAR RAPIDS

DAVENPORT

DUBUQUE

April  5

335

240

263

179

April  6

359

264

287

203

April  7

374

277

300

215

April  8

389

291

314

229

April  9

409

311

333

244

April 10

438

338

358

269

April 11

461

360

382

293


For more details on managing this pest, see http://www.extension.iastate.edu/Pages/eccrops/insect.html>

ASIAN SOYBEAN RUST

The most recent news about Asian Soybean Rust was the discovery of the disease on some Kudzu at two locations near Tamp, FL.  Extensive examinations of host plants is being conducted throughout the south, but so far, the disease has not been sighted elsewhere.  See the third WWW link below.


There are several excellent WWW sites to keep you up-to-date on Asian Soybean Rust.  Some of them are:

Iowa State University Soybeanrust.info http://www.plantpath.iastate.edu/soybeanrust/

USDA Asian Soybean Rust site http://www.usda.gov/soybeanrust/

USDA Asian Soybean Rust location and scouting results http://www.sbrusa.net/

North American Plant Disease Forecast Center ("the North Carolina site") http://www.ces.ncsu.edu/depts/pp/soybeanrust/

North Central Plant Diagnostic Network http://www.ncpdn.org/

National Integrated Pest Management Center Soybean Rust Links http://www.ipmcenters.org/NewsAlerts/soybeanrust/

North Central Integrated Pest Management Center http://www.ncipm.org/

Plant Management Network http://www.plantmanagementnetwork.org/infocenter/topic/soybeanrust/

USDA Animal and Plant Health Inspection Service http://www.aphis.usda.gov/lpa/issues/sbr/sbr.html


In addition, there was an special Asian Soybean Rust edition of the Integrated Crop Management Newsletter.  That edition is at http://www.ipm.iastate.edu/ipm/icm/2005/2-28-2005/asian_soybean_rust_icm.pdf.  The general site for the newsletter is located at http://www.ipm.iastate.edu/ipm/icm/.

Got a Hand Lens?

To correctly identify Asian soybean rust, a good hand lens (20X or greater) is needed. A couple of places to order hand lenses are:

http://www.akmining.com/mine/magnify.htm and
http://gallery.bcentral.com/GID5072838P3166896-Magnifiers-Email-us-for-a-complete-catalog/LOUPE-BAUSCH-LOMB-POCKET-HASTINGS-20X.aspx.  If, by chance, you belong to an organization that would like to use these as a promotional piece, you might check out http://www.promoplace.com/ws/webstore.dll/PrDtl?DistID=8417&RecNum=29&Rec=54925810.

Asian Soybean Rust Fungicides

During the winter meetings, we talked about fungicide usage.  This is a very dynamic areas that is changing every few days.  It now appears that the limitation of two applications of a Section 18 products (the temporarily approved products) will be increased to three, but only two applications of an active ingredient may be used unless the label is even more restrictive.  Remember that you must have in your possession the Section 18 label plus the normal Section 3 label that comes with the product.  The Section 18 labels can be found at http://www.agriculture.state.ia.us/labelsSec18quarantine.htm.

Since the beginning of the meeting season, Stratego and Domark have received Section 18 approval.  In addition, governments and industry are attempting to add additional products to the list.  While there are no guarantees that any of them will be approved, it is also possible they will all be approved.  The ones that use active ingredients already approved are probably most likely to make it through the process for 2005.  Possible additional products include:

Products using currently approved active ingredients:
Absolute (Bayer) - Stratego with the propiconozole (Tilt, Bumper, PropiMax) portion replaced by tebuconazole (Folicur)
Headline SBR (BASF) - Co-pak of Headline and Folicur
Headline Star (BASF) - Pre-mix of Headline and Folicur
Quilt (Syngenta) - Quadris + Tilt

Products using at least one active ingredient not currently approved:
Alto (Syngenta) - cypronoconazole (Triazole)
Caramba (BASF) - metconazole (Triazole)
Charisma (DuPont) - flusilazole (Punch) + famoxadone (Triazole + oxazole)
Headline/Caramba (BASF) - Headline + Caramba Co-pak
Impact (Cheminova) - flutriafol (Triazole)
Operetta (BASF) - Headline + Caramba Pre-mix
Prosaro (Bayer) - tebuconazole (Folicur) + prothioconazole  (Triazoles)
Punch (DuPont)  - flusilazole (Triazole)
Quadris Extra (Syngenta) - Quadris + Alto

Stay tuned regarding the fungicide status by watching http://www.plantpath.iastate.edu/soybeanrust/files/Rust_products_application_notes.pdf, http://www.plantpath.iastate.edu/soybeanrust/files/%20fungicide_cautions.pdf, and http://www.agriculture.state.ia.us/labelsSec18quarantine.htm.

FOR YOUR CALENDAR

Saturday, April 16, 10 a.m. to 3:00 p.m., Transitioning to Organic Workshop, Kalona Family Cupboard Restaurant- - FREE  For producers interested in transitioning from conventional to organic agriculture. Please register by April 14 by sending an e-mail to acmckern@iastate.edu.  For more information, call 515-294-5116 or see http://extension.agron.iastate.edu/organicag/events/transorgworkshopnr.html and http://extension.agron.iastate.edu/organicag/events/transorgworkshop.pdf.

Thursday, June 23, 1:00 p.m. SE Iowa Research & Demonstration Farm Field Day - Crawfordsville  Watch http://www.extension.iastate.edu/Pages/eccrops/meetserc.html as details emerge.

 

If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: April 12, 2005
Contact: Virgil Schmitt vschmitt@iastate.edu


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