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SOIL TEMPERATURES

April 12, 2006

SOIL TEMPERATURES

Soil temperatures have been in the 50's in recent days. 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.

 

SOIL MOISTURE

On April 10, I pulled the usual soil samples to a depth of five feet at a few locations in the counties I cover to assess the plant available moisture as we enter the growing season.  Due to the ground not being frozen for the vast majority of the winter, nearly all precipitation received since crop maturity (or dormancy in the case of perennial crops) has soaked into the soil.  Every location I checked had excellent soil moisture to the feel and all but one location had free water at a depth of four to five feet.  I do not have the official results yet, but all indications are that we have excellent moisture to begin the 2006 growing season.  Soil moisture under hay and pasture may be lower as those plants used moisture later into the fall and already this spring.

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 (Burlington – Mount 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

April  5

177

80.5

99

47.5

April  6

186

84.5

103.5

51

April  7

198.5

89.5

109

52.5

April  8

201

91.5

111.5

53.5

April  9

207

97

117.5

58.5

April 10

220

110.5

130.5

71

April 11

238

124

146.5

82.5


Using National Weather Service forecast temperatures through April 17 and then assuming normal temperatures thereafter, Interstate 80 should reach 200 GDD on April 15 and 250 GDD on April 19, Highway 30 (Cedar Rapids – Clinton) should reach 250 GDD on April 20, and Highway 20 (Waterloo – Dubuque) should reach 250 GDD on May 2.

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.

 

OTHER INSECTS

Stalk Borers Begin to Hatch Soon

Using National Weather Service forecast temperatures through April 17 and then assuming normal temperatures thereafter, stalk borers will begin to hatch along Highway 34 (Burlington - Mount Pleasant area) on April 15, and the hatch will move north, reaching Interstate 80 about April 27, Highway 30 about May 2, and Highway 20 about May 9.  In areas of fields with high grassy weed or giant ragweed pressure in 2005, 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

381.5

196.5

249

137.5

April  6

397.5

207.5

260.5

147.5

April  7

413.5

216

269.5

152.5

April  8

419.5

221.5

275.5

157

April  9

429

230.5

285

165.5

April 10

447

247.5

301.5

181.5

April 11

472

268

324.5

200


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 2006

Corn flea beetles are a common pest in southern Iowa but seldom cause concern further north.  With the mild temperatures last winter, this insect may be prominent much farther north than usual in 2006.  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 2006

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 21 – Thursday, June 22 (9:00 a.m. – 4:00 p.m. each day), Hay Expo 2006 - Strawberry Point, IA.  See http://www.hayexpo.com/ for details.

 

Thursday, June 22, 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.

 

Monday, July 17 (tentative), Muscatine Island Research and Demonstration Farm Field Day (Horticulture) – Fruitland.  Watch http://www.extension.iastate.edu/Pages/eccrops/meetmusc.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, 2006
Contact: Virgil Schmitt vschmitt@iastate.edu


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