vagts crop update vol 2 no 19

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					Crop Update Newsletter Prepared By:
Todd Vagts, ISU Extension Crops Specialist
Serving northwest Iowa

In this issue
 DD50 accumulation and Corn development                              Late summer alfalfa seeding
 Determine pollination success                                       Managing drought stressed alfalfa
 Soybean crop at full pod                                            Mid to late season insect pests
 Harvest corn early to meet forage needs

Introduction
Scattered rain showers and mild temperatures have really helped crop development across west-central
and northwest IA. Yet many areas continue to suffer from extended dry periods, corn harvest decisions
(silage or grain) will need to be determined in relation to feed needs and pollination success. Soybeans
have set pods and will begin seed fill within the week. Fall seeding of alfalfa can be successful where
soil moisture is adequate. Many insect pests continue to feed on crops, including WBC, ECB, Potato
Leefhoppers, Grasshoppers and CRW beetles.

Weather update
The 7 to 10 day forecast looks pretty good for area crop development. Temperatures should hover around
the 90 degree mark during the day and mid 60’s at night. Rain showers prospects look good as well with
good chances of precipitation mid-week.

Growing Degree Day Accumulation and Crop                                                    Figure 1. GDD Acccumulation (7/29)
Development                                                                          2000
A relatively mild week for temperatures last week really
                                                                                     1950
benefited area corn and soybean fields as pollination is
near complete in corn fields and soybeans begin to fill                              1900
pods.
                                                                Accumulated DD50's




                                                                                     1850
                                                                                                 --------------------Dough--------------------
Corn Pollination is complete in most area corn fields                                1800
(check related article on assessing pollination success)
and is advancing towards early dough in the most                                     1750

advanced fields. Most fields are in the R3 stage. R3                                 1700
Stage (Milk) commonly occurs 18-22 days after silking.
The R3 kernel displays yellow color on the outside, and                              1650
                                                                                                --------------------Blister--------------------
the inner fluid is now milky white due to accumulating                               1600
starch.
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Did the corn pollinate? Some areas that have                                  Planting Date
experienced continued moisture stress have questioned          South        North           7-Day Forecast
whether the corn pollinated when silks emerged several
days after pollen shed began. Two methods can be used to determine pollination success

       Carefully unwrap the husks from an ear and check attachment of silks to ovules (kernel). Each
        potential kernel on the ear has a silk attached to it. Within 1 to 3 days after a silk is pollinated
        and if fertilization of the ovule is successful, the silk will detach from the developing kernel.
        Unfertilized ovules will still have attached silks. Silks turn brown and dry up after the
        fertilization process occurs.
       Look for developing ovules (kernels) which appear as watery blisters about 10 to 14 days after
        fertilization of the ovules




                                                   07/29/02
                                               Volume 2, No. 19
Crop Update Newsletter Prepared By:
Todd Vagts, ISU Extension Crops Specialist
Serving northwest Iowa
Soybean Development has reached R3 to R4 in fields across the region. R3 is beginning pod growth. R4
is full pod elongation. This stage marks the beginning of the most crucial period of plant development in
terms of seed yield determination. Continues rain showers across the region will help guarantee good
soybean yields this fall.

Forage
Corn silage to compensate for forage deficit. For those running short on available forage supplies, corn
can be chopped early and fed to meet demand until the crop is ready for normal harvest and storage. In
general, the digestibility and feeding value is equal from blister to maturity. Protein tends to be higher for
more immature silages. On the downside, dry matter intake is typically less with more immature silages,
most likely due to the higher moisture content. If the corn has been under drought stress, nitrate
accumulation may be a concern. Most nitrate problems accumulate in the lower portion of the stalk. By
harvesting a little higher than normal, nitrate problems may be avoided. Of course the most accurate and
safe method to determine nitrate concentration is to send a sample to a lab for testing.

Management of drought stressed alfalfa - Established alfalfa stands as well as new seedings experiencing
drought symptoms should be harvested only if there is enough forage to economically justify harvesting.
If enough alfalfa is present to justify harvesting, the quality of harvested alfalfa should be excellent.
Alfalfa should be mowed or clipped after the drought is broken to stimulate regrowth. This is
particularly important if the alfalfa is blooming, or near blooming, as clipping at this growth stage will
encourage new crown buds to send out new shoots for regrowth.
- Richard H. Leep MSU Crop & Soil Sciences (http://www.msue.msu.edu/ipm/CAT01_field/FC08-09-01.htm#7)

Late Summer Alfalfa Seeding Establishing an alfalfa stand is typically done in the spring, but it can also
be accomplished in late summer in NW Iowa. This procedure can be advantageous with crop rotations
involving small grains or when a spring seeded alfalfa stand did not establish very well. Late summer
seeded alfalfa should only be attempted when conditions allow for it. Refer to the following address for
the full article: http://www.extension.iastate.edu/carroll/crops/summer_alfalfa_seeding.htm

Pest Management
Western Bean Cutworm moth catch continues to decline. Egg masses have been found throughout the
region and some fields have reached treatment threshold. Degree-day accumulation for NW Iowa has
surpassed the 1536 degree-day mark, indicating 75% moth emergence.

        You can monitor current degree-day accumulations and trap catch numbers at the
        following web page: http://extension.iastate.edu/carroll/crops/wbc-2002.htm

Corn rootworm beetle emergence continues and should be near 50%. To check for rootworm damage, dig
a few plants and wash the root mass off with a power sprayer (also works great to soak the root mass
overnight in a bucket of water). Evaluate for feeding on the root system. To review the corn root
damage system (node-injury scale), go to the ISU Corn Rootworm Home page:
http://www.ent.iastate.edu/pest/rootworm/

Potato leafhoppers continue to be a problem in many established and new seeding alfalfa fields. Cutting
the alfalfa often times is the best control strategy for fields near bloom and with infestations over
threshold. After cutting, keep a close eye on the field for continued injury from these pests.
http://www.ipm.iastate.edu/ipm/icm/1999/6-21-1999/potlhmang.html

European Corn Borers (2nd Generation) will be laying eggs soon. Look for egg masses on the underside
of the leaves, three leaves above and below the ear. Go to this IA State web page for a worksheet to use
for control decisions http://www.ipm.iastate.edu/ipm/icm/1996/8-5-1996/ecbcostben.html

                                                  07/29/02
                                              Volume 2, No. 19
Crop Update Newsletter Prepared By:
Todd Vagts, ISU Extension Crops Specialist
Serving northwest Iowa
For further information pertaining to this newsletter; please contact me or any of the county extension offices. This
newsletter can also be accessed on-line at http://extension.iastate.edu/carroll/crops/newsletters_2002.htm. If you
would like this letter to be emailed directly to you, please send an email with the desired email address to
vagts@iastate.edu.


******************************************************************************
Todd Vagts
Iowa State University Extension
Field Specialist, Crops

1240 D. Heires Avenue           Office: 712-792-2364
Carroll, IA 51401               Cell:    712-249-6025
Email: vagts@iastate.edu        Fax: 712-792-2366
Web Page: http://extension.iastate.edu/carroll/crops/homepage.html


Provided to you by:

IOWA STATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
COOPERATIVE EXTENSION


                   Iowa State University and U.S. Department of Agriculture cooperating

Extension programs are available to all without regard to race, color, national origin, religion, sex, age or

                                                     disability.




                                                      07/29/02
                                                  Volume 2, No. 19

				
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