The corn fungicide dilemma: when should a fungicide be applied? Part IV of V, standability/lodging

Much has been made of the ability of strobilurin fungicides to prevent corn from lodging, typically towards the end of the season.  Since 2007 I have received countless calls that have gone something like “we sprayed a field with fungicide A, and the field right next to it that didn’t receive a fungicide is laying on the ground following the storm on Saturday but none of the corn that received the fungicide fell over.”  Having conducted fungicide trials at 28 different locations over a three year period, the MSU researchers involved in the Mississippi Corn Promotion Board funded trials hoped to see some differences in standability/lodging between treated and untreated plots.  First of all, lodging can occur as the result of numerous situations.  Disease, wind, lack of nutrition, herbicide injury resulting in rootless corn syndrome (typically early in the season), or even insect damage can all lead to lodging.  Notably, there are two specific types of lodging: root lodging and stalk lodging.  Root lodging occurs when a force acts to disrupt the point of root/soil attachment such as a major wind event (i.e. straight-line wind).  Stalk lodging can be the result of a force that causes the stalk to snap at a particular location which can be referred to as “greensnap” throughout the season. 

In 2009, two corn fields received straight-line wind events.  One of the fields, near Shaw, MS was not harvested following our research trials due to the extensive nature of the lodging across the entire field.  The field was still rated for the presence of foliar disease as well as data that were collected during destructive plant sampling but it was decided harvesting the field would result in extensive time delays for the producer on our part.  The 26 other fields observed during the three year study had little or no lodging and in general lodging was not a variable rated.

Lodging from rated portions of the whole plot was visually rated on a scale of 1-12 (Horsfall-Barrett, where 1 = 0% and 12 = 100%) at the same time as foliar diseases.  The two corn fields in question were treated with fungicides (Headline, Propimax, Quilt) at tassel (VT) and treatments included a non-ionic surfactant at a rate of 1.0% v/v.  Fungicides were applied by air in 5 gallons of water. 

Low levels of lodging, based on Horsfall-Barrett scores of 1 to 2, were encountered at the Schlater, MS location (data contained within Tables 1 & 2).  Based on the Horsfall-Barrett scale a rating of 1 would be 0% while a rating of 2 would be 0 to 3% so based on the average of the 4 reps some plots had only a little more than 0% lodging.

Severe lodging, characterized by the majority of the field having received a major wind event that resulted in extensive lodging occurred at the Shaw, MS location (data contained within Tables 3 & 4).  Lodging scores ranged from 6 to 8 on the Horsfall-Barrett scale where a 6 is 25 to 50% of the plot and an 8 would be 65 to 87% of the plot lodged.  Low levels of foliar disease, generally less than 5% on a whole plot basis, were identified at this location and the destructive sampling rated variables (ear feeding, ear rot, staining of the bottom node, root rot, and stalk rot) were similar to those from the Schlater, MS location as well as the other 26 locations rated over the three year study.

Generally speaking, there were no significant differences between plots treated with a fungicide, regardless of the active ingredient(s), and the untreated plots with regards to the amount of lodging sustained.  In addition, low levels of foliar disease and pathological variables rated during destructive sampling means that foliar or stalk diseases were not to blame for the high levels of lodging sustained at the Shaw, MS location.  Put simply, a fungicide should be used in a situation where it prevents yield loss from a disease that has been reported to result in a reduction in yield. 

Part V will present data from a trial in Stoneville, MS where southern corn rust resulted in a situation where yield was lost in untreated plots.