Early Season Cotton Planting Concerns for 2008
I have looked at the long-term forecast for Raleigh (http://nc.weather-forecast.ws/raleigh) which goes from today, May 28 through May 5). I have used this site, http://www.weather.com/weather/tenday/27695?from=36hr_topnav_undeclared for May 6th and 7th. Based on this prediction we do not really start accumulating heat units until the May 1st. Heat units are calculated by adding the high and the low, dividing that number by 2 and then subtracting 60
[(*F Max + *F Min Temp)/2] - 60 = DD60s.
You can update these numbers for you local conditions and for changes in the forecast that will likely become more accurate closer to the actual day of planting.
Here is a look at how heat units(DD60's) are predicted for the next 10 days.
| Date | High Temp | Low Temp | Daily DD60's | Predicted DD60 accumulation for the following 5 days |
| April 28 | 72 | 50 | 1 | 22.5 (April 28-May 2) BEWARE see* |
| April 29 | 68 | 46 | 0 | 30.5 (April 29-May 3) BEWARE see* |
| April 30 | 71 | 52 | 1.5 | 38.5 (April 30-May 4) BEWARE see* |
| May 1 | 78 | 60 | 9 | 45 (May 1 - May 5) |
| May 2 | 83 | 59 | 11 | 45.5 (May 2 - May 6) |
| May 3 | 78 | 60 | 9 | 45.5 (May 3 - May 7) |
| May 4 | 79 | 57 | 8 | |
| May 5 | 79 | 57 | 8 | |
| May 6 | 79 | 60 | 9.5 | |
| May 7 | 79 | 63 | 11 | |
*although DD60 accumulation is adequate to very good, low night time temperatures during the early germination may cause stand loss problems.
We normally do not recommend planting cotton prior to April 15. Conditions from April 15th until now have been cool and have not provided any really good windows for planting. The following table relates 5 day DD60 accumulation to planting conditions.
The predicted 5–day DD60 accumulation for planting on April 28 is considered adequate and the 5-day DD60 accumulation for both April 29th and April 30th is considered very good base upon the above table; however, growers probably want to avoid planting these days because low night time temperatures when the seed first imbibes water can be very detrimental to germination. The figure below shows how critical the temperature is during the first day of germination. This is when the seed first imbibes water.
If a grower feels like they need to plant during this period they should make sure they are planting on well drained soils with high seed quality.
The high cost of seed makes it more important that growers consider seed quality. In cotton there are two common germination tests, standard germination and cool germination. Standard germination results are reported on the seed tag. Standard germination tests are conducted at 86 degrees F for sixteen hours per day and 68 degrees F for 8 hours per day. In North Carolina it is highly unlikely that all of the cotton seed you plant will benefit from this close to ideal conditions.
The test that is of more practical value to growers in North Carolina is the cool germination test often referred to as "cool germ". Cool germ tests are not reported on the seed tag. The seed companies run this test on all seed and the dealer or distributor usually has this information. If not, the value can be obtained by calling the seed company with the lot number of the seed. NCDA can run cool germ tests on your seed if needed.
What is considered to be "good" cool germ results? Being aware of the cool germ results is probably more important than what is actually a good or bad cool germ. As long as you are aware of the cool germ values for a given seed lot you can plan accordingly. A somewhat arbitrary division of cool germination values follows in Table 2.
Cool Germ Value |
Ratings - Comments |
under 50 |
bad - most companies would not sell this seed |
50 - 65 |
acceptable - use special care with this seed |
65 - 80 |
good |
over 80 |
superior |
2008 - Carolina Cotton Notes
