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CROP UPDATE 4/5/2007

April 5, 2007

Most of the following comes courtesy of Virgil Schmitt:

 

Corn-On-Corn Issues and tips

If you will be growing corn-on-corn for the first time in several years, you may want to review several items found at http://www.extension.iastate.edu/Pages/eccrops/Corn-On-Corn.html.  You will find both economic and production tips there.  The link to one recording is not functioning because the recording is currently unusable; we will get it up and running ASAP.  The files found there are fairly large, which may be problematic for dial-up connections.

 

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 full 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 Highway 34 (BurlingtonMount Pleasant area) and very soon north of Highway 34.  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

March 26

176

117

135

89

March 27

198.5

132.5

151

102

March 28

215.5

136

156

103

March 29

228

139.5

160

106

March 30

245

145

165

108.5

March 31

261.5

156.5

177

116.5

April 1

270

157

179.5

117.5

 


Using National Weather Service forecast temperatures through April 8 and then assuming normal temperatures thereafter, Interstate 80 should reach 200 GDD on April 10 and 250 GDD on April 18, Highway 30 (Cedar Rapids – Clinton) should reach 250 GDD on April 21, and Highway 20 (Waterloo – Dubuque) should reach 250 GDD on May 1.

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 2006.

How Has the Recent Cold Weather Affected Alfalfa & Alfalfa Weevils?

Temperatures in the teens and low 20s will at least cause some tissue damage in established alfalfa fields, and could cause more serious damage to the buds and crowns. Tissue damage often causes the leaves to have a near white appearance. It will take a week or more to determine if the cold temperatures have caused any permanent damage to the alfalfa. If the re-growth is showing evidence of freeze damage, plants should be dug and crowns split to check for damage. Healthy taproots are creamy-white in color, with a firm texture. Freeze-injured taproots will begin to be ‘watery’, tan/brown in color and beginning to soften. See Steve Barnhart’s article on the agronomy website for more information: http://www.agronext.iastate.edu/showitem.php?id=39.

The good news is that the cold temperatures should have killed any early hatched alfalfa weevils. Eggs are more protected though, and probably survived. Most eggs have not yet hatched, so assuming they survived, the current cold weather will not likely have a large impact on the weevil population.

 

OTHER INSECTS

Stalk Borers Begin to Hatch Soon

Using National Weather Service forecast temperatures through April 8 and then assuming normal temperatures thereafter, stalk borers will begin to hatch along Highway 34 (Burlington - Mount Pleasant area) on April 16, and the hatch will move north, reaching Interstate 80 about April 28, Highway 30 about May 2, and Highway 20 about May 9.  In areas of fields with high grassy weed or giant ragweed pressure in 2006, 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

March 26

313

205

243

159.5

March 27

342.5

227.5

266

179.5

March 28

366.5

238

278

186

March 29

386

246.5

287

194

March 30

410

259

299

203

March 31

433.5

277

317.5

217

April 1

449

281

323.5

222


For more details on managing this pest or for updated information on the development of this pest, see http://www.extension.iastate.edu/Pages/eccrops/insect.html.

 

Corn Flea Beetles in 2007

Corn flea beetles are a common pest in southern Iowa but seldom cause concern further north.  With the mild temperatures much of last winter, this insect may be prominent much farther north than usual in 2007.  In addition to the physical damage caused by corn flea beetles, the beetles also act as a vector for Stewart’s Disease.  Most commercial corn hybrids are resistant to this disease, but some are susceptible, and many corn inbreds and many sweetcorn varieties are susceptible.  As corn emerges, be sure to scout for this insect.  Information on scouting, thresholds, and management can be found on pages 63 – 64 of the May 7, 2001 Integrated Crop Management Newsletter or at http://www.ent.iastate.edu/Ipm/Icm/2001/5-7-2001/fleabeetleexpect.html.  In addition to what is stated in the article, Poncho 250 and Cruiser 5FS (at the 0.125 milligrams per kernel rate) seed treatments also provide early season protection against corn flea beetles.

 

Bean Leaf Beetles in 2007

The mild winter may have also allowed very good survival of bean leaf beetles.  Information on managing the overwintering population can be found on pages 81 – 82 of the May 27, 2002 Integrated Crop Management Newsletter or http://www.ipm.iastate.edu/ipm/icm/2002/5-27-2002/manageblb.html.  In addition to what is in the article, Cruiser 5FS provides excellent protection from the overwintering bean leaf beetles.  Also, watch http://www.extension.iastate.edu/Pages/eccrops/insect.html as the season progresses.



FOR YOUR CALENDAR

Wednesday, June 20 – Thursday, June 21 (9:00 a.m. – 4:00 p.m. each day), Hay Expo 2007 - Westgate, IA.  See http://www.hayexpo.com/ for details.

 

Thursday, June 21, 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 5, 2007
Contact: Jim Fawcett fawcett@iastate.edu


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