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Georgia Cotton: Liberty Control Of Pigweed Depends On Time Of Day

Owen Taylor
By A. Stanley Culpepper, Extension Weed Scientist, University of Georgia June 8, 2012 19:51

Georgia Cotton: Liberty Control Of Pigweed Depends On Time Of Day

During winter meetings, Georgia growers were presented research results showing how the time of day influenced Liberty (Ignite) activity on Palmer amaranth during 2011 (Figure 1). Control ranged from 8 to 97% in response to the time of day in which applications were made.

Control from applications made around 12:30 am and 6:45 am provided 8 and 50% control, respectively. In contrast, mid-day or late afternoon applications provided excellent control (97-99% control).

Additional studies are in progress to better understand this interesting time of day impact on Liberty.

Figure 2 shows the level of Palmer amaranth control from a single Liberty application made from one hour before sunrise up through 6 hours after sunrise; results suggest applications should not be made until at least one hour after sunrise.

Figure 3 shows the level of Palmer amaranth control from Liberty applications made 6 hours before sunset through 1 hour after sunset. Control with afternoon/evening applications were more stable when compared to morning applications but the data does suggest less control may be achieved as the sun sets.

Applications of Liberty to Liberty Link cotton pose no significant injury risk regardless of the time in which applications are made. However, response of Widestrike cotton is more complex (Figure 4).

As expected, Widestrike cotton injury from Liberty applied alone is greatest during mid-day applications (similar to Palmer control).  It is important to note, the addition of Dual Magnum or Warrant with Liberty would increase the level of injury noted regardless of the time of day applications are made BUT the greatest level of injury would now most likely be observed with early morning applications to cotton covered in heavy dew when followed by a hot sunny day.

Just as a reminder, we do not recommend or suggest applications of Liberty be made to any cotton other than that containing Liberty Link technology.

There has been a significant push to include ammonium sulfate (AMS) with Liberty. So far, research has shown the impact from AMS (regular spray grade) to Liberty often causes:

Reduced Palmer control with early morning sprays.

Minimal to no benefit of Palmer control with sprays during other times of the day.

Potential to increase the level of cotton injury regardless of application timing. Therefore, we strongly encourage growers do not use AMS for in-crop applications of Liberty.

These 2012 research efforts are currently being conducted at 2 GA locations as well as a location in Tennessee, North Carolina and Louisiana. The early results from the Tennessee location (Larry Steckel) are similar to our results. By this winter, we should have a very good understanding on how time of day influences control of Palmer amaranth by Liberty across the Southeast and Mid-South.

Owen Taylor
By A. Stanley Culpepper, Extension Weed Scientist, University of Georgia June 8, 2012 19:51