Northwest Iowa Crop Update Newsletter by Todd Vagts ISU Extension Crops Specialist Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.
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Volume 2, Number 19

Northwest IA Crop Update, July 29, 2002
(Word Document)

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

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 Development
A relatively mild week for temperatures last week really benefited area corn and soybean fields as pollination is near complete in corn fields and soybeans begin to fill pods.

Corn Pollination is complete in most area corn fields (check related article on assessing pollination success) and is advancing towards early dough in the most advanced fields.  Most fields are in the R3 stage.  R3 Stage (Milk) commonly occurs 18-22 days after silking.  The R3 kernel displays yellow color on the outside, and the inner fluid is now milky white due to accumulating starch.

Did the corn pollinate?  Some areas that have experienced continued moisture stress have questioned 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

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 (2^nd 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

(Word Document)