Research Accomplishment Reports 2007

Helping Kentucky Growers through the Adverse Weather Conditions of 2007 Growing Season

J.R. Martin, J. D. Green, and W. W. Witt
Department of Plant and Soil Sciences

 

Project Description

Several weather events occurred during the 2007 growing season that impacted weed management decisions throughout much of Kentucky. The warm temperatures in late February through March provided a favorable environment for early season plant growth.  This unusually warm period ended abruptly April 5th when temperatures dipped into the teens at night and stayed in the 40’s during the daytime for a period of 5 days. Following the unexpected freeze, the precipitation levels fell nearly ten inches below normal from April 1 through mid October.  The duration and severity of this drought set records for many communities in Kentucky.

Impact

Because of the unusual conditions horseweed (Conyza canadensis) control was erratic where 2,4-D was used in preplant burndown applications.  This raised concern among some growers that 2,4-D tolerant biotypes had developed tolerance to this herbicide. Preliminary results of greenhouse studies conducted by Dr. Witt suggest these are susceptible to 2,4-D and that other factors played a role in poor control.  This type of response helps reassure growers that 2,4-D continues to be a valuable option for managing this weed in no-till systems.  Without 2,4-D, growers may have to resort to tillage which costs more than ten dollars per acre than no-tillage and promotes soil erosion.

It is estimated that approximately 104,000 acres of wheat were either harvested for hay or silage or treated with a burndown herbicide to convert damaged fields to full season soybeans or corn as a result of the April cold front.  Extension worked closely with the Kentucky Department of Agriculture to develop Section 18 labels to allow wheat growers to harvest their crop for hay or silage where Harmony GT or Harmony Extra was applied.  The fact these herbicides are used on approximately 75% of the wheat made these Section 18 registrations extremely valuable to wheat growers who harvested wheat for hay or silage.
It is estimated approximately100,000 acres of early planted corn had to be replanted due to poor stands.   Growers had limited opportunities to control the surviving corn plants when the original planting was a glyphosate-tolerant hybrid.  Studies were conducted to evaluate options for managing glyphosate tolerant hybrids.  Although the research was too late to react to this season's events, these data will be beneficial for future reference.

The dry conditions that prevailed through the summer months caused concern that atrazine would persist longer than normal and injure fall planted crops such as wheat or spring crops such as soybeans.  This herbicide was used on nearly one million corn acres this past season in Kentucky, consequently a large number of acres could be impacted due to atrazine persistence and carryover to rotational crops. Soil samples were collected from strategic sites in Kentucky and analyzed under the direction of Dr. Witt.  Results showed no detectable atrazine or extremely small quantities of the herbicide in the soil; consequently the risk of injuring such rotational crops as wheat or soybeans is very unlikely.