Note – This is a message from UGA Extension Cotton agronomist Dr. Jared Whitaker. For more information on the UGA Cotton Team, visit http://www.ugacotton.com.
Weather is a big factor that all cotton producers have to consider during planting season. In Georgia, rainfall is almost always limited at some point and our producers are some of the most experienced in “making it work”.
This year was no exception as conditions deteriorated quickly, where rainfall became increasingly rare anywhere across the state between May 14th and June 3rd. On top of the dry weather, air temperatures soared between May 26th and June 3rd. This left conditions exceedingly poor for most of the state and producers who were finishing planting during this time faced an extremely difficult task.
Ultimately, many (if not most) fields which were planted during the window between May 26th and June 3rd ended up having to be replanted.
Replanting occurs on a small percentage of our crop each year, but this situation was unique as stands were inadequate in fields where producers did everything right and used all the tricks and tools we have to help emergence during less than optimum conditions.
Most of the time when a cotton field has to be replanted there is some issue that we can point to which helps explain what happened and give hints to what could be done differently next time.
This time I visited growers across the state with stand issues that occurred during this window and time after time there was not obvious issue that would explain why we failed at getting a stand. The only common thing was that germination seemed to slow down and seedlings seemed to “run out of gas”, which was backwards to the common idea that emergence is faster as soil temperatures rise. We did measure soil temperatures in a lot of fields during this window and documented temperatures at 1” below the surface well over 100° F in wet soil and over 120° F in drier soil. We’ve seen soil temperatures this high many times before, but rarely see it last over a week.
Looking back, there was quite a bit of literature that provided evidence to indicate that cotton emergence slows and is ultimately limited when soil temperatures rise above 95° F. Specifically, that research has shown that temperatures even slightly over 95° F can significantly limit the emergence process. There are several physiological processes that are negatively affected when temperatures rise above 100° F, yet the work ultimately suggests that the seedling emergence process is not efficient and the process slows, in some cases to the point where seedlings don’t make it to the soil surface prior to running out of energy (ending in seedling death).
Some of this temperature related cotton seedling work has indicated that seedling vigor, or inherent differences in vigor, can significantly impact how much these adverse conditions play a role in emergence. In Georgia, most of our best variety choices are considered to be extremely small seeded varieties. We know that seed size is very closely correlated to seedling vigor, as seed size decreases, vigor decreases (and vice versa). This is not something that is seed company or brand specific, but rather simply a function of energy storage. So, it should not be surprising that when a larger seeded variety is planted next to a smaller seeded variety, when conditions are poor, one could see differences in overall emergence.
In hindsight, we had some extremely poor weather conditions for almost half of our planting window and almost impossible conditions during a particular week. Knowing what we know now, there were obvious situations where a bag of seed with better vigor could have made the difference in getting a stand. However, making variety decisions only based on vigor in Georgia could leave yield potential on the table.
With weather predictions becoming increasingly better, we may be able to know when this will happen again. However, we still need to have better information on how seed from a particular bag will respond. Currently, we only know that seed we buy has adequate vigor to emerge in a standard germination test, which is conducted with temperatures up to only 86° F. We can also make inferences based on seed size and in some cases have the results of a cool germination test.
As much as producers pay for cotton seed, I think it’s fair to say that we need better information on what happens when soil temperatures rise to risky levels. There are other germination tests out there, specifically an accelerated aging test, which may provide key information needed to help make the decision on how to choose a variety when seedling vigor becomes increasingly important. More times than not, we plant cotton in soil temperatures that are well above 86° F and testing information that reflects that could make all the difference in whether or not we get an adequate stand of cotton in early enough to maximize yields.
This article is certainly not meant to challenge current germination testing procedures or to say that growers should make rash decisions based on recent experiences, but rather to encourage our industry to strive to provide Georgia producers with variety decisions which don’t make us settle on sometimes “lower than needed” vigor. In the meantime, we need to work to ensure that we have the best information possible to make good decisions when these scenarios occur again in the future.
After all that, let’s hope for a successful 2019 cotton crop. Even though much of the crop suffered early on, the weather has made a turn for the better in most places and with a favorable August we could make an extremely good if not record crop.
For any question or issue with your cotton crop, be sure to reach out to your local UGA County Extension agent.