Weather
Dry conditions have prevailed over much of Iowa over the last two months; some areas have been much drier than others.  Large precipitation events in June and the first few days in July make summer precipitation totals look adequate, yet a dry period from early July through August have left many areas without any appreciable precipitation events for 58 days.   Good subsoil moisture reserves have greatly aided area crops through the dry period, but in many cases yields have suffered due to moisture stress.
 

Row-Crop and Forage Development
How much yield “Potential” did the area lose in August?  This question has been weighing on most peoples minds and is anyone’s guess as to what the real numbers might be.  To help alleviate my own curiosity, I looked to my computer where I have been working with a crop (corn and soybean) simulation model which uses local climatic conditions to mimic crop growth and development and to generate an estimate on final yield.  I ran the model with updated weather data about every two weeks this summer to get an updated picture of how the corn and soybean crop was doing. (The model needs a full year’s worth of weather data to operate, so I use 2003 weather data up to the day I run the model, then I use previous year’s weather data (2001 and 2002) to finish the year out.)  Yield “potentials” were high and relatively stable up through August 1, indicating little crop (weather) stress up to that point.   I then ran the model on August 26 (replaced 26 days of “previous years” weather data with current data) which then gave a good picture of how 2003 August weather may have affected area crops. 

The results indicated a decline in “Potential” grain yield of 24% – 30% for corn and 45% - 48% for soybean. 

Before this information is taken to the bank (or coffee shops); a few key points must be stressed with this data.  The “potential” yield that the model generated on Aug 1 was very high, indicating very good growing conditions up to that point.  A significant drop in yield potential may still result in good or average yields for both crops.   Additionally, local field results will vary widely depending on site specific soil conditions, planting date, hybrid/variety grown, precipitation, rooting capacity and soil fertility.  And finally, weather data was collected from only two points in west-central IA which may not reflect other field locations across the state.    

Stalk rot scouting Late season drought stress can greatly enhance stalk rot problems in corn fields, resulting in lodging problems before harvest.  Scouting involves looking for lower stalk discoloration and test stalk firmness by pinching the lower internodes between your thumb and forefinger. Healthy stalks are firm and won't compress easily. If a node can be compressed or otherwise feels soft, rotting has started that plant is a good candidate for lodging. Check at least 100 plants per field, in representative locations. Fields with different tillage systems that are in different rotations, planted to different hybrids or with different fertility histories should be scouted separately. If more than 10-15 percent of the stalks show rot damage in a field, significant lodging is likely.  If possible, harvest high lodging potential fields early. And don’t forget to record the stalk rot incidence in field records so you can use this year’s problems to avoid future problems.

Information on Harvesting and Storing Drought Stressed Crops can be obtained from this web URL:
http://www.exnet.iastate.edu/Pages/grain/news/03drought/03drought.html

Soybean Aphid Update:  Treatment of soybean aphids is now completed. It’s important to collect information from treated vs. non-treated strips. Useful information is a yield comparison and aphid population estimates. Take a picture if dramatic differences are noted between the treated and untreated areas.  Pictures and 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 09/05/03