Watch Temperatures to Time Harvest Aid Application

Cotton  defoliation and harvest progress has ceased due to current rainfall patterns through the weekend and the first part of the week.  Rainfall reports have ranged from 1.5 to 3 inches depending on location.  Cotton yields have been reported as low as 500 lbs lint/A on dryland to over 1300 lbs/A irrigated.  Only approximately 10% of the cotton crop was harvested prior to the rain.  Hurricane Issac and other storm systems have caused lodging in many fields as well as hardlock problems especially in Southeastern counties.  Cool temperatures are moving in today and overnight to lows forecasted in the upper 40′s.  Very few of the harvest aids that we have available will have any effect during low temperature periods.  The table below can be found in the defoliation guide (http://www.uaex.edu/Other_Areas/publications/PDF/MP503.pdf) and includes common harvest aid materials and their low temperature thresholds. 

Harvest aids containing thidiazuron (Dropp, FreeFall, others) become less effective when low temperatures drop below 65° F.  Folex, Finish,and Prep begin to reduce activity when temperatures fall below 60° F.  Most herbicide products such as Aim and ET will provide a little more activity with their low temperature threshold somewhere around 55° F.  One reason for the reduction in activity of all these harvest aid products relates back to plant processes.  Warm conditions (>65° F) provide for active plants and leaves that become more receptive to harvest aid applications.  Once a boll opener or defoliant is applied, active plants increase the amount of ethylene produced to hasten the abscission layer resulting in quick leaf drop and boll opening.  Under cool conditions, the plant processes slow tremendously thus making the plant less receptive and less responsive. 

Harvest aid applications will be more effective if they are delayed until temperatures reach a more optimal level.  Usually the plant will become much more receptive two to three days after a cool front moves through.  With this in mind, I would delay all harvest aid applications until temperatures increase and the plants have time to recover. Right now it looks like Friday may be a day to start applications.  If the second application is made this week, products such as Aim or ET will be less affected by the cooler conditions than FreeFall or Folex.  Boll openers will be much more effective if applications are delayed until Friday.  If made during this cool snap it will take an extended amount of time to notice application benefits.