Weather
Soil moisture has been in abundance for much of the summer, but in some areas of west-central and north-west IA, rain showers have been hard to come by since the first week of July.  Soil moisture deficits may start to affect corn and especially soybean yields in these areas.  Audubon, Fort Dodge, Holstein and Rockwell City have not seen a precipitation event greater than a ¼ of an inch for at least 20 days.

Corn degree-days (Base 50) Degree-day accumulation continues on a near normal track from last week through the next seven days with 156 DD’s forecast for this week.  Degree-days (average for NW Iowa) can be accessed at this web site:  http://www.extension.iastate.edu/carroll/crops/degree-days-2003.htm

Corn Development Corn Pollination is complete in most area corn fields and is advancing towards early dough in the most advanced fields.  Many 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.  Ear tip kernel abortion occurs when the youngest kernels resulting from the most recent pollination are cut off from nutrient flow because the supply is insufficient to fill all the kernels that have been set. Such kernel abortion is most likely to occur during the first two weeks after pollination (Blister stage).

Soybean Development has reached R3 to R4 in fields across the region.  R3 is beginning pod growth.  R4 is full pod elongation.  Pod wall elongation occurs over a period of about 20 to 25 days. Pods reach maximum length before seed growth occurs. At the time of full pod wall extension, only 4 percent of the maximum seed weight has accumulated.  R4 marks the beginning of the most crucial period of plant development in terms of seed yield determination. 

Forage: Harvest corn silage to compensate for forage/feed deficit.  If you are  running short on feed supplies, corn can be chopped early (on a daily basis) and fed to meet demand until the crop is ready for 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 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.

2^nd generation ECB scouting should take place in late maturing non-B.t., seed-production and popcorn fields.  Fields that have green silks and are shedding pollen are most susceptible to second-generation infestation.  Each egg develops a black spot just before hatching. Best control is realized when application is timed to the first significant egg hatch and when young larvae are still located in the leaf axils.  As the plant approaches blister stage and beyond, potential economic benefits of an insecticide application rapidly decline.

Yield loss from the 2nd generation ECB occurs mainly from physiological yield loss (reduced yield from reduced water and nutrient uptake through the stalk).  Several worksheets (some interactive on the web (http://www.ianr.unl.edu/forms/forms.skp/ecb_2nd.html) have been developed to help you make the decision on whether to treat the pest.  These worksheets can be access online at http://www.ipm.iastate.edu/ipm/icm/1996/8-5-1996/ecbcostben.html or http://www.ianr.unl.edu/pubs/insects/nf365.htm

Western Bean Cutworm moth catch has declined significantly in areas south of Highway 7 but continues to increase in areas to the north, particularly in Buena Vista and Clay counties.  Scouting for egg masses and hatched larva should be ongoing in these areas.  Pay close attention to pre-tassel corn.

Monitor current degree-day accumulations, trap catch numbers, and look at pictures of egg masses and newly hatched larva at the following web page:  http://extension.iastate.edu/carroll/crops/wbc-2003.htm

For questions or comments please respond to vagts@iastate.edu

This page last updated on 08/04/03