Command Injury Symptoms Reemerge in Sweetpotato Fields

Stephen Meyers, Sweetpotato Extension Specialist
By Stephen Meyers, Sweetpotato Extension Specialist August 16, 2013 16:29

Command Injury Symptoms Reemerge in Sweetpotato Fields

Command Injury-Cocklebur

Earlier this week I received a photo via text.  The photo showed white-leafed cocklebur plants in a sweetpotato field in Chickasaw County.  The sender was curious as to what would cause this.

Command (active ingredient: clomazone) is the most frequently used herbicide in Mississippi sweetpotato production.  It is typically applied within 48 hours after transplanting in May and June.  This early season, post-transplant application of Command is almost always evident by the whitening of weeds and hardwood tree species on a sweetpotato field’s edge.  Commercially-grown sweetpotato varieties have a high degree of tolerance to Command.  Even sweetpotato plants exhibiting classic interveinal whitening symptoms will grow out of the injury with very little to no reduction in yield.

It is somewhat unusual to see Command injury in sweetpotato fields in mid-August.  However, cocklebur plants, with their extensive root system, are a great Command-indicator plant.  There has been no shortage of escaped cocklebur this year in sweetpotato fields across northeast Mississippi.  If the field in question did not contain so many escaped cocklebur, the activity would likely have gone undetected as there were no symptoms on the sweetpotato vines.

Persistence of clomazone in Mississippi soils is dependent upon numerous factors including soil texture, pH, and rainfall.  The average half-life of clomazone is 24 days, but can range from 16 days in sandy loam soils to 36 days in silt loam soils.  Clomazone is only moderately sorbed to soil and has moderate water solubility.  Heavy rainfall occurring just prior to the symptoms appearing likely increased the amount of clomazone in the soil solution that was taken up by the cocklebur.  Unfortunately, the large cocklebur plants that are white this week will almost all be green next week.

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Stephen Meyers, Sweetpotato Extension Specialist
By Stephen Meyers, Sweetpotato Extension Specialist August 16, 2013 16:29
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