Introduction
More “normal” temperatures should dominate the region this week and will help advance crop development towards maturity.  Overall the region is about 10% behind normal in degree-day accumulation, or about 12 calendar days.  Now is a good time to do the end of year field scouting to identify weed, insect, fertility and compaction issues that should be remedied for next year.  Another disease, Powdery Mildew, is showing up in area soybean fields.  Some recent thunderstorms have caused lodging of corn fields, read up on the best ways to harvest those fields.  The last cutting of alfalfa should be taken now so that a good 6 (frost free) weeks are available to build up root reserves.   Continue scouting for soybean aphids to monitor the length of persistence.

Row-Crop and Forage Information
Growing Degree-day Continued below average degree-days last week made for continued slow crop development.  Last week the area accumulated 133 degree days, 5% less than the average of 140.  The 7-day forecast shows warmer days, but cool nights with an accumulation of 129 degree-days, which should be the same as the 13-year average.    Seasonal total degree day accumulations for April and early May planting dates remain at yearly lows when compared to the 13-year average (87 to 91% of normal).  This equals about 225 degree-days (about 12 calendar days) behind normal.  Degree-days (average for NW Iowa) can be accessed at this web site:  http://www.extension.iastate.edu/carroll/crops/degree-days-2004.htm

Corn development Most corn in the area should be near dent to approaching full dent by the end of the week. 

Lodged Corn?  Strong storms over the last week have caused some lodging in area corn fields.  The University of MN has released a document that I think may be helpful with harvest decisions (http://www.extension.umn.edu/cropenews/2004/04MNCN24.htm)  See also information from 2002:  http://www.extension.iastate.edu/carroll/crops/reducing-harvest-losses.htm

Drought stressed corn for silage:  Some areas in extreme west-central and northwest IA have experienced drought stress in the corn crop with little relief in sight.  Predicting when to harvest drought stressed/damaged corn for silage can be challenging.  But as long as the plant has grain, the dry down rate of the grain will provide a rough guide for predicting whole plant moisture.  In some cases even when all the visible leaves have turned brown, the whole plant moisture is still above 70%.  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

Soybean Development:  Estimate soybean yield potential. 

• Estimate the number of plants per acre (measure an area 1/1000 of an acre and count the number of plants within the marked area.)

• Count the number of pods on ten randomly selected plants within the marked area and calculated the average number of pods/plant

• Calculate pods per acre by multiplying plants/acre by pods/plant

• Calculate seeds per acre by multiplying pods per acre by an estimate of 2.5 seeds/pod

• Calculate pounds per acre by dividing seeds/acre by an estimate of 2900 seeds/pound

• Estimate yield by dividing pounds/acre by 60 lbs. per bushel.

The formula is: [(plants/acre) x (pods/plant) x (2.5 seeds/pod)] / (2900*60) = Estimated Yield bu/acre

This formula uses several estimations and therefore may be variable depending on the final number of seeds per pod and seed weight.  (Source: Corn and Soybean Field Guide, 1997; Purdue University Coop Extension Service)

Forage and Pasture Management
Give alfalfa a rest before winter.  The timing of the last harvest of alfalfa affects its winter survival and next spring's vigor. Alfalfa needs about six weeks of uninterrupted growth in the fall to become fully winterized. Dr. Barnhart (ISU’s Extension Forage Specialist) recommends that for the best survival of the stand, attempt to take the last summer cut by late August or very early September, and let regrowth stand in the field.  http://www.ipm.iastate.edu/ipm/icm/1999/9-13-1999/alfalfaman.html

Pest Management
Scout and evaluate corn and soybean field health now while you have time.  Many disease, insect and weed pest problems can be found in area corn and soybean fields now.  Obtaining a positive ID on a disease, weed or insect will be very important when making crop rotation, hybrid and variety selection decisions for next year.  Be sure to utilize the ISU plant disease clinic (http://www.extension.iastate.edu/Pages/plantpath/pdcintro.html), and/or the ISU weed, insect and soil fertility specialists when confronted with an unknown problem.  When scouting fields, be sure to dig plants and examine the root system, the lower stalk area, split stems and collect soil and plant samples for further testing if the problem is not easily identified.

Soybean Maturity, Drought stress or Disease?  A number of soybean fields have expanding yellow areas in recent weeks. In some cases, the fields are reaching normal physiological maturity. But in fields that have yellow patches and still have green pods, other factors may be occurring in the field that should be investigated. A cumulative effect of drought stress, disease, nutrient deficiency and soybean Cyst may be the problem.

Powdery Mildew has been showing up in area soybean fields, find information and pictures of the disease at this URL:  http://www.psu.missouri.edu/soydoc/files/disease/powdery.htm

Soybean Aphid  Scouting for soybean aphid should continue, but the need for treatment should be very carefully evaluated.  We are most likely past the point of economic return for most soybean fields.  Refer to last year’s treatment response curve to see the effectiveness of aphid treatments in late August:  http://www.extension.iastate.edu/carroll/crops/Aphid%20form%20results%20graphed.pdf.  Yet scouting should continue so that you have an idea of how long the aphids persist and to what degree the aphid population grows.  Refer to this page for more information on identification, scouting and temperature and humidity trends compared to last year.  http://www.extension.iastate.edu/carroll/crops/soybean-aphid.htm  

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

The information given in this publication is for educational purposes only.
Reference to commercial products is made with the understanding that no
discrimination is intended and no endorsement by Iowa State University with
any specific product(s) used in this is implied

This page last updated on 08/30/04