Crop Update and Four Bract Squares

Darrin Dodds, Extension Cotton Specialist
By Darrin Dodds, Extension Cotton Specialist June 22, 2012 17:17

In general, the cotton crop in Mississippi appears to be in good shape.  Some areas are beginning to need some rainfall; however,  a few fields just got water off low areas a few days ago.  Blooms are becoming more prevalent and over the next two weeks I expect a large portion of this crop to be blooming.  Plant growth regulator and layby applications are being made and irrigation will start soon.

A few calls have been received regarding four bract squares over the past few weeks so I figured I would provide some information regarding the phenomenon.  The incidence of occurrence is much lower than in 2011.  Four bract squares typically occur to some degree every year. 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 earlier than normal due to favorable weather conditions during early and mid-April.  Generally, most of the cotton planted during this time has had little to no four bract square formation.  Cotton that was planted slightly later seems to be the cotton in which this is occurring this year.  Day and nighttime temperatures from approximately May 24 through May 28 were well above average the overall average was near 80.  During this time microscopic squares were likely located in the terminals which may account for the appearance of these squares. Given the low incidence of occurrence, the levels that we are seeing may also be naturally occurring.

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.  In addition, taking a more aggressive stance to anything that causes square loss may be warranted.

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Darrin Dodds, Extension Cotton Specialist
By Darrin Dodds, Extension Cotton Specialist June 22, 2012 17:17
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