Weather
Scattered showers are forecasted through the week with temperatures in the 90’s through Thursday.  Friday ushers in a huge change in temperatures as the area will be looking at highs in the 70’s and lows in the 40’s.

Corn degree-days (Base 50) The late season heat wave extended through last week and will continue through mid part of this week, greatly advancing crop development.  176 degree days were accumulated over the previous seven days and 146 degree days (near normal) are forecasted for the next seven days.  The vast majority of the coming week’s degree-days will be accumulated over the next 4 days.  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 Silage-harvest under drought conditions:   (Provided by Dr. Stephen Barnhart, ISU Extension Forage Specialist) One of the main management challenges of harvesting drought damaged corn for silage is cutting the plant at the proper moisture content. In plants with at least some grain, the dry down rate of the grain will provide a rough guide for predicting whole plant moisture.  Plants with no grain, and some live green leaf tissue still evident, will have surprisingly high moisture content (75 - 80%); too high for direct cut and ensiling. In some cases even when all the visible leaves have turned brown, the whole plant moisture is still above 70% moisture.  The strongest take home lesson for livestock producers with drought-damaged corn is to not be too hasty to 'get in to the corn field'. As long as the corn plant is still alive it will be accumulating some additional dry matter.  Each developmental stage of corn growth will add several tons per acre of dry matter to the potential harvested product.  Detailed information on harvesting corn for silage can be accessed at the following web site: http://www.uwex.edu/ces/crops/uwforage/Silage.htm

Fall Management of Drought Stressed Pastures (Provided by Dr. Stephen Barnhart, ISU Extension Forage Specialist) Most grass and legume/grass pastures are overgrazed and have gone dormant; whether or not rain has fallen. Fertilizer will do little to stimulate growth while the pasture plants are dormant, but when adequate soil moisture and cooler autumn temperatures return, stressed pasture plants will respond to applications of fertilizer, particularly nitrogen. Consider applying 30 to 60 lb/A of nitrogen to pastures during late August to stimulate recovery of pasture plants and autumn forage. A significant volatilization loss of nitrogen can occur from surface applications of urea forms of nitrogen. Consider using the ammonium nitrate form if available. If urea is used, time the application just before a rain to minimize the exposure time of urea on a dry soil surface.

Insect Pest Management
Soybean Aphid Update:  How much longer will we have to fight the aphids; is probably your biggest question.  We are not sure how long the aphids will be here, but they could be here until frost or at least soybean maturity.  There are indications though that some field populations have stabilized or are on the decline.  In my observations, I would say the extended warm temperature has limited aphid population growth to the mid-canopy area where temperatures are milder.  I have not been finding many aphids on the upper ¼ of the plant.  Some key criteria to evaluate when making treatment decisions include: 1) how many aphids are on the plant (1000 – 1500 is a heavy load), 2) is the population increasing, decreasing or stabilized, and 3) how much yield does the plant have yet to set (how much yield needs protecting)?  To determine how much yield is already in the pod, reference these charts:  http://www.extension.iastate.edu/carroll/crops/soybean_aphid_yield_set.htm  

In most situations, soybean maturity and insecticide pre-harvest intervals will most likely stop any treatments made after late this week.   Be sure to include all aphids (including the small, pearly white aphids) in your counts.

How much yield is in the pod?  How much yield still needs to be protected?  Use these charts to get an estimate on the % of potential yield is in the bank:
http://www.extension.iastate.edu/carroll/crops/soybean_aphid_yield_set.htm

More information on soybean aphids can be found at:
http://www.extension.iastate.edu/carroll/crops/soybean-aphid.htm

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

This page last updated on 08/25/03