Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


July 27, 2005

July 27, 2005





The much needed rainfall that finally came yesterday means that we still have the potential for respectable corn yields in many fields that have soils with good water holding capacity. The extreme heat and drought conditions of the past few weeks have no doubt taken a toll on potential corn yields in the area, but fortunately we started off the season with the soil at field capacity in most fields. The extreme heat that occurred in the past week came after pollination was complete, and it appears that there was good pollination in many of the area corn fields. Most corn is in the R2 (blister) stage now and moving into R3 (milk). The high humidity that came with the heat should have reduced the stress on the crops somewhat. In the area I cover, Benton County and areas immediately adjacent are in the best shape, and the further east and south you go from Benton County, the drier it has been. We will obviously need to continue receiving some good rains through the rest of the season, since the soil moisture reserves have been depleted. Corn needs about 5-6 inches of moisture in July and 4-5 inches in August. For a map showing an estimate of the rainfall in the past week see Its nice to finally see some color on the map for the area.

August is usually the most critical month for soybeans, so we should still have the potential for good soybean yields if we have some good August rains. Soybeans in many fields are in the R3 stage now (beginning pod) and moving into R4 (full pod). Stresses from R1 (beginning flowering) to R3 usually do not reduce yields because some flowers and pods can still be produced until R5 (beginning seed) to compensate.




Two Spotted Spidermites


Spider Mite problems that I have heard about have mainly been east of the Cedar Rapids-Iowa City area. Hopefully the rain and cooler temperatures will help to reduce problems with the pest. See the last ICM Newsletter for more information at


Soybean Aphids


Soybean Aphids can still be found in most fields in the area, but in low numbers. They are most numerous on the underside of newly developing trifoliates, including younger trifoliates low in the canopy. On fields that I have looked at there have been less than 50 aphids per plant in most cases. The economic threshold is 250 aphids per plant and increasing. At this level it is recommended to spray an insecticide to prevent the level from reaching the economic injury level of 1000/plant where the damage caused equals the cost of treatment. Under the right conditions, populations can double in 2-3 days, so 250/plant can increase to 1000/plant in less than a week. The heat has probably kept populations in check, but its possible that they may increase more rapidly with these cool temperatures, so fields need to continue to be monitored closely. For more information on soybean aphids see and the July 11, 2005  ICM Newsletter at

Asian Soybean Rust


No news is good news. For the latest see




Western Bean Cutworm


The western bean cutworm has not been a widespread problem in EC and SE Iowa, but did cause damage last year in some corn fields in the northern part of the area. Moth traps are again located throughout the state, and there have been some large moth captures, especially in Benton, Linn, and Jones Counties. Scouting for the pest is encouraged to continue until 7-10 days after the peak moth flight. The peak moth flight occurred from July 18-22 at some sites in Benton, Linn, and Jones counties, so scouting should continue for a few more days. You can check on moth catches at An insecticide is recommended if egg masses are found on 8% or more of the corn plants and when 70-90% of the eggs have hatched out. Some fields have been sprayed in the past week for the pest, especially in western Iowa. For more information see the last 2 ICM Newsletters at and




Potato Leafhopper


Potato Leafhopper numbers continue to be high in many fields, so scouting of hay fields continues to be an important activity.  For information on managing potato leafhopper, see pages 107 - 110 of the June 21, 1999 Iowa State University Integrated Crop Management Newsletter or A couple of sources for sweep nets are and


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: July 27, 2005
Contact: Jim Fawcett

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