Key Corn Verification Findings

The goal of the MSU Corn Verification Program is to increase profitability of corn grown in Mississippi cropping systems.  We seek to accomplish this goal by implementing good practices and technology capable of reducing production limitations and risk when warranted.   We also try to enhance timing and/or execution of important inputs, so the crop may respond much better to those variables. We are also devoting resources available in this program to identify key production limitations, so the Mississippi State University Extension Service and Experiment Station can better direct efforts to develop innovations for our specific problems.  By doing so, Mississippi’s entire agricultural industry, including growers, crop consultants, suppliers, retailers, and consumers will benefit.  This is a summary of such limitations documented during the past few years.

Planting performance significantly affects corn productivity:  Verification fields were evaluated in 2010 to document the effect of stand variability on corn grain yield.  Plant population and plant spacing variance were measured and plots were hand harvested to determine the extent of variability common within fields and its effect on corn productivity. We sampled 2010 verification fields identified areas within fields with good or uneven spacing for analysis. Results summarized from last season’s Corn Verification Program showed good, uniform plant spacing  improved grain yield an average of 44 bu/a or 19% within these fields.  Thus, this offers tremendous potential for us to enhance corn productivity, so we intend to focus efforts upon optimizing planter performance to improve plant uniformity.  Our methods to improve uniformity may include reducing planter ground speed, thorough calibration, and use of mechanical enhancements.  Of course, we also cannot afford to plant when soil temperature and moisture are not conducive to rapid seedling growth and root development.  

Ryegrass control is imperative:  Glyphosate resistant ryegrass is now documented in 12 counties in the Mississippi Delta and ALS resistant populations also exist in 14 counties.  Correspondingly, ryegrass populations are generally increasing and becoming much more difficult to control in crop fields.  One of the 2010 verification fields had a slight to moderate ryegrass population present after the corn crop emerged.  Postemergence herbicide application selected to optimize ryegrass control provided moderate control (60-70%).  However, surviving ryegrass plants grew rapidly and competed strongly with young corn plants.  We documented the level of crop competition by marking areas within the field and hand sampling to assess ryegrass population and corn grain yield response, prior to combine harvest.  Results indicated a population of one ryegrass plant per seven square feet reduced corn grain yield 65 bu/a or 27%, compared to corn with no ryegrass competition.  This indicated we should aggressively and proactively address this specific weed issue.  MSU Weed Scientists and Agronomists have since developed and published new strategies, and hosted a field day and numerous educational events to improve ryegrass control in corn and other row crops.

Exceptionally early planting can lead to stand shortcomings:  Rainy conditions and wet soils normally restrict corn planting until soil temperatures are adequate for rapid germination and vigorous seedling development.  Thus, we often begin corn planting whenever soils are dry enough to plant.  However, cold soils may also inhibit stand development.  Two five to six day cold periods (0 GDD 50’s) preceding and subsequent to plantings during the first week of March 2009 limited germination and exacerbated effects of heavy rainfall following planting.  Cool soils also persisted through mid-March 2010, but did not inhibit stands as much as 2009, because rainfall and soil saturation were far less.  Corn seed germination requires temperatures of at least 50 deg F and proceeds faster when temperatures are higher than this minimal level. This led to corn stand problems, particularly in clay soils and/or poorly drained areas, of fields.  We suggest always using a thermometer to make sure soil temperature is favorable for rapid seedling germination and emergence prior to planting.

Seed treatments have some pitfalls:  We have found substantial insect damage during early vegetative stages in corn verification fields during the past several seasons.   Plant damage has occurred, despite the presence of insecticide seed treatments on seed designed to limit seedling injury.  The primary pests causing damage have been Sugarcane beetles and Stink bugs.  Sugarcane beetles have caused considerable damage in several cases and have primarily been occurring in dryland fields in the hills.  After noting minor damage (often 2-3% stand loss) in 2008, we chose to utilize enhanced seed treatments levels (“500” vs “250” level) in all verification fields.  However, one verification field still suffered damage to at least 25% of plants from Sugarcane beetles.  MSU research has shown the primary commercial seed treatments, Poncho and Cruiser, differ considerably in Sugarcane beetle control.  Sugarcane beetle damage in Poncho treated seed was about 70% less than seed treated with Cruiser.  Thus, we have discussed this issue with corn seed companies and chemical manufacturers to hopefully instigate changes necessary to provide Mississippi growers the resources to address this issue.  Otherwise, in order to effectively address this, we  may be limited to specific hybrids, which provide viable insecticide options.

New technology offers improved weed control:  Combining glyphosate with residual herbicides can provide good seasonal corn weed control in many cases.  However, application timing and herbicide selection can substantially affect performance, as well as expense warranted.  Several new herbicides which are bleachers or pigment inhibitors have enhanced weed control effectiveness, compared to the traditional standard of atrazine/metolachlor  (Bicep II Magnum) when tank mixed with glyphosate.   We have used either Lexar tank-mixed with glyphosate or Halex GT (+atrazine) in Roundup Ready Corn Verification fields with substantial weed populations.   These herbicides have substantially improved weed control, particularly residual control of morningglory species. Utilizing this combination in an early postemergence time frame (V3-V5 or 6-12” corn) has also improved seasonal weed control, compared to preemergence herbicide timing, particularly when planting before soil temperatures climb well into the mid-60 deg F range (~mid-April depending on latitude and seasonal temperatures), when warm season annual weeds normally begin germinating.  However, reliance on postemergence herbicide application can be trying, when frequent rainfall restricts ground application, as in 2009, or covering large acreage. 

 Management can improve nitrogen use efficiency:  We devote considerable effort to improve crop response to nitrogen by using appropriate nitrogen sources, application timing and application methods to ensure more nitrogen is utilized by the crop, rather than potentially lost to adverse environmental conditions.  The South’s warm, high rainfall climate greatly increases potential nitrogen loss through denitrification and leaching, compared to drier and colder climates.  Springtime denitrification losses can be very substantial when soils remain saturated for extended periods, such as in 2009, particularly in heavier, clay soils.  We try to apply nitrogen fertilizer at specific times according to corn need — in other words “spoon feed” the crop using a split application strategy using a small portion of nitrogen just after plants emerge, followed by the bulk of the nitrogen fertilizer just before rapid growth stages, when the plants need it most. We found this method worked extremely well in springs with abundant rainfall, like 2009, when we were able to employ it as desired.  For example, comparing a verification field to a cooperator’s base program, the verification field nitrogen timings were each delayed two to three weeks later than the base program.  Thus nitrogen applied in the base program was subject to loss during very adverse, saturated conditions for about five weeks more than the verification field.  Our cooperator applied 100 lbs/a of urea treated with a urease inhibitor to compensate for anticipated loss, whereas the verification field was able to forego this application.  Harvest results estimated by yield monitor showed similar or better grain production in the verification field, despite receiving less fertilizer.

Field scouting can play an important role in disease management:  The verification program has allowed us an opportunity to intensively manage the crop for diseases and prove we can save money in doing so. Research at MSU, universities in neighboring states and across the United States have shown little or no evidence that an automatic fungicide treatment at the tassel stage is capable of enhancing corn grain yield or other plant health or growth parameters in the absence of disease infection.  Therefore, our approach is to use management practices which reduce the likelihood of foliar disease development and use routine field scouting to monitor the crop and justify fungicide use when there is a high likelihood of generating a profitable response.  We strongly encourage routine rotation of corn with other crops to reduce the significance of our primary foliar diseases which survive on corn residue, such as northern and southern leaf blight, gray leaf spot, and anthracnose, compared to the southern corn belt, where continuous corn, reduced tillage systems have made these diseases a common, annual occurrence.  We also closely evaluate and recommend hybrids with resistance to foliar diseases, particularly for fields following corn grown the previous season.  Furthermore, we routinely scout fields for disease development.  Many foliar diseases of corn, including the leaf blights and spots, initially infect lower leaves, and then spread up the canopy, because the fungus that causes them can survive in infested corn residue on the soil surface.  Higher humidity also promotes initial infection low in the canopy.  Thus, regular scouting has allowed us ample opportunity to identify disease infection and recommend timely fungicide application, before the critical upper leaves are infected.  Ultimately, you can relate these factors to crop growth stage to determine potential crop risk and likelihood of profitable response for making prudent management decisions.