Four Bract Squares in Mississippi Cotton

Although many are aware of the issues that have been created by the appearance of four bract squares over the past few weeks, the magnitude of this issue warrants a final few words.  First and foremost, four bract squares typically occur to some degree every year.  However, the incidence appears to be much higher in 2011.  In some cases four bract squares have been discovered when flared squares appear and fruit retention numbers begin to decline in the absence of insect pressure.  Although there is not a tremendous amount of research on this phenomena, average day/nighttime temperatures above 80°F in the first few weeks after cotton emergence appears to be a primary factor in the formation of four bract squares.

A cotton plant can begin square initiation as early as the time the second true leaf expands.  Generally, about 40 days prior to bloom microscopic squares are located in the terminal of a cotton plant.  High temperatures during this time cause the meristem to attempt to form an additional leaf.  This extra leaf eventually forms a fourth bract.  The formation of a fourth bract can prevent the square from “sealing” and thus allow an entry point for thrips, plant bugs, etc.  In some instances, the fourth bract appears to stick to the fruiting structure itself.  As the fruiting structure expands, the square will generally flare and fall to the ground.

Most of our cotton was planted somewhat later than normal due to difficult weather conditions which was followed by abnormally warm temperatures during the first two to three weeks of June.  Cotton that was planted during mid-May likely had microscopic squares located in the terminals during the two to three weeks of high temperatures.  Subsequently we have seen an increased number of four bract squares in 2011.  The table below illustrates the effect of planting date and heat unit accumulation on the formation of four bract squares.  These data were collected by Dr. Chris Main at the West Tennessee Research and Education Center in Jackson, TN.

The lower fruiting branches appear to be the most susceptible to the formation four bract squares.  Many folks are reporting that the issue with four bract squares is beginning to correct itself.  In other words, fruit from lower branches may have been lost; however, as new fruiting branches and squares have formed they appear to be a normal three bract square and are not flaring as some four bract squares have previously.  If you have lost fruit due to four bract squares, or other factors, a more aggressive approach to managing vegetative growth will likely be necessary.  Keep a keen eye out for internode elongation and make appropriate plant growth regulator applications as growth, soil type, soil moisture status, variety, and other factors dictate.