Twisted corn and other "opportunities"
by Micheal D. K. Owen
June 14, 2005 -  The recent weather has resulted in rapid development of the 2005 corn crop.  We have gotten an number of calls about "twisted" or "wrapped" corn.  While it is impossible to eliminate a herbicide effect, it is more likely that earlier cool weather have more to do with these developmental issues.  Dr. Bob Nielsen from Purdue Univesity has an excellent article posted on his website.  There are numerous pictures included with the article that provide some reference to the relative severity of the problem.  Also, while Dr. Nielsen does not provide a definitive answer to the cause of the problem, he does give some interesting insights to the issue.

It is also anticipated that this rapid growth of the 2005 corn crop, accompanied by the high winds and thunder storms, may cause some stand loss attributable to stalk brittleness.  Contributing to this can be postemergence applications of plant growth regulator (PGR) herbicides such as 2,4-D and dicamba.  There have been several situations this year where stand loss has occurred due to brittle stalks caused by the PGR herbicides. If applications of PGR herbicides (or any postemergence treatments on corn, given the current stage of development) are planned, directed post applications are highly recommended.

In areas where corn was planted into "too wet" soils, and seed furrow closure was poor, or side-wall smearing occurred, "rootless" corn problems may surface.  Corn may "fall over" inexplicably, and upon inspection, a poor root system discovered.  The problem has been observed in conservation tillage as well as no tillage fields this year.  Careful cultivation may help the problem on smaller corn but it may be best to leave larger corn alone and hope the problem resolves itself.. 

Finally, the other current concern is that many corn fields ( and soybean fields, for that matter) have not had the postemergence herbicides applied.  Many fields are past due for timely postemergence herbicide treatments, and it is suggested that these fields have already experienced some potential yield reductions due to weed interference.  Given the environmental conditions, postemergence herbicide applications of ALS inhibiting products and pigment inhibiting products are best made as directed applications.  While the herbicide label(s) may describe broadcast applications, and realistically, directed postemergence treatments are not a convenient option, treatments over the top of corn represent a risk for crop injury.  Unfortunately, in many fields, weed populations are a sure bet to reduce yields.  Thus, in some cases, the risk of crop injury is likely less than the risk of yield loss.  Hope for moderate weather conditions and do the best you can.  Maybe cultivation is a better option at this time?  It is advised that due consideration be given to the risks associated with postemergence programs and it is recommended that growers strongly consider a two step preemergence/postemergence weed management program in the future. 

 Prepared by Micheal D. K. Owen, extension weed management specialist, Department of Agronomy, Iowa State University