Reviewing Winter Wheat Herbicides

        One of the first orders of business for winter wheat is to evaluate weed pressure.  While winter wheat is generally quite competitive against most summer annual weeds, winter annuals like mustards (field pennycress, shepherd’s purse, wild radish, etc.) pose a bit more of a problem.  If these weeds have a density and size that warrants control, there are several postemergence herbicide options available for use. 

        There are two key factors to consider when selecting herbicides for winter wheat.  First, the selected herbicide must have good activity against the weed species that are present.  The cheapest alternative, 2-4-D, is good on mustards, but weak on wild buckwheat and smartweed.  Dicamba products like Banvel and Clarity are good on wild buckwheat and smartweed, but generally weaker on the mustards.  The sulfonylurea herbicides like Harmony GT and Harmony Extra are becoming popular but a bit more expensive herbicides for winter wheat.  They offer a bit better crop tolerance and provide excellent control of mustards. 

        The second important consideration with wheat herbicides is the maximum wheat growth stage when they should be applied.  In particular, late applications of dicamba or 2,4-D can cause kernels to abort and leave blank heads.  Both herbicides need to be applied before the jointing stage.  The sulfonylurea products should be applied after two leaves but before the flag leaf is visible.
 

Soil Temperature and Corn Planting 

            We often equate corn-planting time with soil temperature, but the fact is that in most years it's calendar date that starts the planters rolling.  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.  Soil temperature will mirror air temperatures on a daily basis. After April 25, IF soil conditions are good for fieldwork, don't hesitate to begin planting corn (even though actual temperatures remain 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.
 

Do I need to use corn starter fertilizer?

     Using starter fertilizer for corn has been standard practice in Wisconsin for many years.  This is not the case in some other states where all plant nutrients are often applied as a broadcast application in the spring or fall.  Each spring, questions arise as to whether fertilizer needs to be applied at planting.  The major disadvantage to such a practice is that it slows down the planting operation because time is spent filling dry or liquid fertilizer holding units on the planter.  Also, many fields already have excessively high levels of phosphorous (P) or potassium (K) and the need for adding more nutrients as a starter fertilizer is justifiably questioned.

     To help answer these starter fertilizer questions for corn, University of Wisconsin soil scientists initiated a large research project in the late 1990’s that involved 100 replicated starter fertilizer comparisons on farms throughout the state.  Essentially, fertilizer treatments were compared on each farm where a starter fertilizer was used or was not used.  Most of the locations involved fields with high or excessively high P and K levels.  Depending on the year, positive economic response to starter fertilizer occurred 32 to 48 percent of the time.  Corn yield responses ranged from –10 to +42 bushels per acre.  

     Results from these on-farm trials showed that corn hybrid maturity, planting date, and soil test K levels were the major site-specific factors affecting corn yield response to starter fertilizer.  Contrary to conventional thinking, the probability for profitable yield responses was highest at later planting dates for any given corn hybrid relative maturity (R.M.), especially when soil test K levels were less than 140 ppm.  Any combination of circumstances that pushed the limit on corn maturity (e.g. excessively long R.M. corn planted anytime but especially late) increased the odds for positive economic response.  Planting a short-season hybrid early in the spring resulted in the least likely scenario for positive response from using a starter fertilizer.

     Site-specific management decisions need to be made.  For sites with excessively high levels of P and K, we still recommend to apply a minimum rate of starter fertilizer of about 10-20-20 (N-P-K) pounds per acre.  It's highly unlikely that a yield response will be obtained by applying nutrients beyond this level.  Even at this rate, early planting of a short season hybrid is unlikely to result in additional yield.  For fields having optimum or high soil test levels, higher than minimum starter fertilizer rates will be needed to provide the entire crop P and K requirement, or use the minimum starter fertilizer rate at planting and supply the additional needed nutrients with a broadcast application.  For heavily manured fields, apply only the minimum 10-20-20 rate.