Dave Verbree and Tyson Raper
As of 8/26/14, this cooler than normal year has set cotton back by 166-215 heat units depending on the planting date (Table 1). Based on the 30-yr average, we typically accumulate about 18.5 DD60s/day during this time of year which puts our cotton 9-12 days behind schedule. However, we have been accumulating about 23 DD60s/day over the past 5 days which is helping us catch up. Unfortunately, the number of DD60s per day normally begins to drop about 0.2 degrees each day at this time of year.
We need about 1625 DD60s to reach 1st open boll and some of those who planted timely, did not over-fertilize, and managed for earliness are already there. We need about 2200 DD60s to reach maturity so we hope the above average temperatures will stick around a few more weeks. Realistically, most of us should expect cool temperatures during defoliation and plan to use a two-pass approach, relying more on our herbicidal defoliants to finish off the job. We will post more about defoliation in the coming weeks.
Table 1. Accumulated heat units (DD60s) for Jackson, TN by planting date.