Take the Soybean Aphid “Treated vs. Non-Treated” yield check strip survey.  Depending on how much information you want to provide, the form should take between 1 and 5 minutes to fill out.  The larger the data base of treated and non-treated strips I can gather, the better the information this area will have for future soybean aphid infestations. 

Please find the “Treated vs. Non-Treated” on-line and printable form at these URL’s:
http://www.extension.iastate.edu/carroll/crops/aphid_treatment_form.htm  (on-line form)
http://www.extension.iastate.edu/carroll/crops/Soybean%20Aphid%20Insecticide%20Treatment%20Survey.pdf (For Printing)

Refer back to the “Aphid Page” for survey results when thy become available.  (http://www.extension.iastate.edu/carroll/crops/soybean-aphid.htm).

Grain Moisture Content for Safe Storage (by Paul Kassel, ISUE Crops Field Specialist)

Soybeans – sold by spring                   14.0 %
Soybeans – stored up to one year        12.0 %
Corn - sold by spring                          15.5 %
Corn – stored 6 – 12 months               14.0 %

Harvest losses – rules of thumb.

Corn Harvest Losses

• 2 kernels per sq. ft. equal one bu/a loss.

• One ear per 125 feet of 30-inch row equals one bu/a loss.

• One ear per 100 feet of 38-inch row equals one bu/a loss.

Soybean Harvest Losses

• 4 soybeans per square foot equal one bu/a loss.

• Be sure to include soybeans in uncut stubble.

Hidden Soybean Yield Loss:  When soybeans are harvested below 13% moisture, yield is lost.  For example: 50 bushel per acre soybean yield at 9 % moisture equals 2.4 bushel per acre hidden soybean yield loss (13% moisture minus 9% moisture equals 4 points of moisture times 0.6 bu/point/acre hidden yield loss, or 2.4 bushel per acre).   

What is a killing frost?  The first killing frost for Northern Iowa is forecasted for the 1st of October.  Most row crops at this time have reached or nearly reached physiological maturity, so a killing frost should not have any impact on crop yield potential.  But what constitutes a killing frost?  For corn, soybean and sudangrass, temperatures at or below 28 degree Fahrenheit for several hours would be a killing frost.  Alfalfa is generally more tolerant, being able to withstand temperatures to 25 degrees Fahrenheit without severe foliar damage. 

Is frosted alfalfa toxic?  (Information provided by Stephen Barnhart, ISU Extension Forage Specialist)  Frost injured alfalfa, clovers, and the commonly used perennial cool-season forage grasses Do NOT have the potential to form hydrodynamic acid, are NOT considered toxic and can be safely grazed or harvested for hay or silage following a frost.  There is probably a slightly higher bloat risk for grazed alfalfa and white clover the first few days after a frost.  Follow normal bloat preventing grazing management when grazing alfalfa and clover.

Managing frosted sorghum sudangrass and sudangrass.  (Provided by Stephen Barnhart, ISU Extension Forage Specialist) The potential for prussic acid poisoning and management suggestions are related both to the size of the plant when frosted and the extent of frost damage. Prussic acid, more correctly called hydrocyannic acid (a cyanide based compound) is formed in sudangrass or sorghum sudangrass hybrids which are severely stressed or frost damaged.  The hydrocyannic acid develops within a few hours after the frost and usually dissipates within a few days. 

The safest management is to remove cattle and sheep from frosted fields for several days.  Livestock can be returned to frost injured sudangrass that is 18" or taller and sorghum sudangrass 30" or taller after about 3 or 4 days.  If the grass was shorter than these heights when frost injured, withhold cattle and sheep for 10 days to 2 weeks following the frost to avoid problems. Then watch for new shoot regrowth, (tillers or “suckers”) on partially frost killed plants! Direct grazing of these fresh new shoots can be toxic too. Where new shoots appear following frost, avoid grazing until 2 weeks after the "killing" frost that kills the new shoots.

Frost damaged sudangrass or sorghum sudangrass hybrids can be cut and stored as silage.  Sudangrass and sorghum-sudangrass hybrids are difficult to dry thoroughly enough for safe storage as dry hay.  As with wilting and ensiling, most if not all of the hydrocyannic acid is dissipated in the drying process.

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

This page last updated on 09/26/03