Evaluation of a six variety planting date trial in Jackson has indicated that when cotton was planted has an impact on development of four bract squares (FBS).  Six hundred squares were examined for each planting date listed in Table 1 data is presented as percent of squares that had a fourth bract averaged across six different varieties. Only four out of six planting dates were evaluated since squares are just becoming visible for June 1^st and June 15^th planted cotton. These dates will be evaluated later when the squares can be easily examined. FBS incidence increases from 3.5% for April planted cotton to 15% in May 5th planted cotton, to 28% for May 20th planted cotton.

Table 1. Percent of squares having a fourth bract in planting date trials, Jackson, TN 2011.

The major factor to consider is how quickly heat units are accumulated. Table 2 compares heat unit accumulation for the first four weeks after each planting date. Notice that the May 20^th planted cotton accumulated nearly twice as many heat units as the May 5^th planted cotton in four weeks.  Heat stress is  major factor in the development of FBS.

Table 2. Weekly heat units accumulated after planting, Jackson, TN 2011.

Finally, differences were noted among varieties with FBS percentages ranging from 6-40% in the May 20^th planting date. The earlier maturing the variety the more FBS were present. Additionally the more determinate the variety more the FBS were present. In other words, earlier more determinate varieties had the most FBS followed by early indeterminate varieties, and later maturing indeterminate varieties had the least FBS. Over the next few days we will evaluate square loss on varieties with high and low FBS percentages. Stay tuned for more information.