Some Corn Planting FAQ's

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

Is soil temperature an issue when planting corn?

     Corn germination and growth doesn't begin until soil temperatures reach 50 degrees F.  For this reason, many producers won't begin planting until they are absolutely positive soil temperatures reach and stay at this level. For ultra early corn planting dates, this is probably a good rule to follow. However, we have reached the point in 2001 when soil temperature should have NO bearing on the decision to plant corn.  Soil temperature will now mirror air temperatures on a daily basis. IF soil conditions are good for planting, don't hesitate to begin planting corn (even if actual temperatures are below average) if you have large acreages to get planted. Target May 10 - 15 as dates to be done with corn planting.  After this, the proverbial yield penalty for late planting begins on full-season hybrids.  It takes about 125 Growing Degree Units (GDU's) from planting to emergence.

Does corn seed size affect grain yield?

     The genetics of the parent plant, environmental conditions during seed field development, and the position of the individual kernel on the cob influence corn seed size.  Seed from a single ear could fall into many size/shape classes.  Large-rounds usually come from the base of the ear, flats from the center, and small-round seed from the tip.  Seed size has been a valid indicator of vigor for some crop species.  However, corn isn't one of them.  Numerous research studies have evaluated the relative performance of size/shape combinations and have found few differences in emergence, growth, or grain yield.  Obviously, planter performance can be an important issue with small seeds if maintenance or proper set-up is lacking.  Bottom line:  Don't compromise on genetic potential and seed quality simply to obtain a desired seed size.

Do I need to adjust corn seeding rates when planting corn for silage versus grain?

     Optimum final stands for most corn hybrids are in the 28,000 to 32,000 plants per acre range. Are higher final stands needed to maximize corn silage yields?  Most university and private seed company research indicates that there is not a benefit for having final stands over 35,000 plants per acre for corn harvested as silage.  In fact, as final stands increase beyond this level, forage quality begins to decline.  Thus, there is no reason to significantly increase seeding rates (assuming you are already in the optimum range) when planting corn for silage versus grain.

Are non-conventional corn rootworm treatments effective?

     Every year I get questions regarding the use of non-conventional products for controlling corn rootworms as replacements for traditional insecticides.  These include products such as sulfur, turpentine, soybean meal, dry molasses, kelp, fish meal, diatomaceous earth, and kerosene.  Typically, someone will use one of these products for a year or two and not have a rootworm problem.  The immediate assumption is that the non-conventional product was effective.  In fact, there were probably no rootworms to control and the grower would have been better off to use nothing.

     All of the above mentioned products have been university tested in field plots with known economic insect pressure from corn rootworms.  All of them failed and were no better than “check” treatments where no control measure was used.  Crop rotation and corn rootworm beetle scouting are still the only effective methods to reduce insecticide use on corn acreage unless you simply want to take your chances and use nothing.  The latter approach will be effective most of the time but may prove disastrous in a year and/or field where rootworm populations are high.