According to the Missouri Crop Progress and Condition Report for the week ending August 3rd, our cotton is 24 days ahead of last year and 20 days ahead of normal. The higher temperatures this year have led to a much earlier crop and the loss of yield potential for the non-irrigated cotton. While I was at Columbia last week at the University of Missouri's Bradford Farm, I was amazed at how wet the fields were. They have been having problems all year long with rain affecting their planting and replanting, loss of fertilizer, and weed control. We were not able to go into the herbicide injury plots because it was too wet. We settled for a PowerPoint presentation indoors. To put this in perspective, the North Central Region still has 26 percent of their fields affected by excess moisture and the Northeast Region has 70 percent surplus. This means that it's too wet for most field operations in several of the counties in those regions.
The US Drought Monitor shows that all of the lower Bootheel counties are considered moderate drought. There is also an area to the west and north of us that is considered abnormally dry. This website can be located at http://www.drought.unl.edu/dm/monitor.ht.... If you look at the 12 week animation, you can see that we became abnormally dry around the 22nd of June and it has become increasingly drier since then.
While I attended the Crop Injury Diagnostic Injury Clinic, we heard an excellent presentation about the climate and problems associated with it. The reason for our weather patterns is blamed on the El Nino-Southern Oscillation (ENSO). This is a weather pattern that occurs on average every five years. Generally, it is about 3-7 years for the entire cycle. It is characterized by variations in the temperature of the surface of the tropical eastern Pacific Ocean - warming or cooling known as El Nino and La Nina, respectively - and air surface pressure in the tropical western Pacific - the Southern Oscillation. According to the speakers, El Nino is winding down and we are in a transition to La Nina. This phenomenon affects the jet stream. El Nino is Spanish for the child or boy and it gets its name because the weather changes often change around Christmas. La Nina is Spanish for the girl and it has an opposite effect.
I also learned that the Bootheel typically follows the weather patterns in the Southeast U.S. rather than the patterns of the rest of the state and the Midwest in general. Looking at forecasts from the National Weather Service, it is unlikely that we will get relief from the heat anytime soon. Since August is typically a dry month, it is expected to remain dry.
I have been keeping up with our cotton development all season long. In summary, we had enough moisture to get the cotton up and we had enough temperature for the crop to develop very quickly. All of this has come to a halt with the dry conditions. Much of our irrigated cotton looks pretty good but there are exceptions. On some of the sandier fields, constantly running the center pivots hasn't met the total moisture needs of the plant. While it is enough for plant survival, it's not enough for optimum yields.
With the hotter summer conditions, the early plant maps looked good. After the plants begin to bloom, we can look at the nodes above the white bloom to see what is happening to the crop. At the beginning of blooming, we would expect to see 8-11 nodes above the last white bloom. We were in this range in the irrigated cotton. However, the non-irrigated cotton was not as fortunate. Physiological 'cutout' is the final stage of cotton plant growth prior to boll opening and characterized by predominance of more mature fruit, general absence of squares and blooms and cessation of new terminal growth. According to more recent terminology, cotton is approaching cut-out at five nodes above white bloom. At the Delta Center earlier this week, I learned that they had already reached 'cutout' by the end of July. A heavy boll load on the plant will cause this to happen.
In our area, we are interested in the last effective bloom date. This is the average date in which a bloom on the plant will have enough heat units to mature the bloom into a harvestable boll. The average date in our area is August 15. So we would like to see the cotton reach 'cutout' around that time. If it occurs too early, then we are not able to take advantage of the entire growing season. This appears to be the case this year.
I have mentioned that most of the cotton that sets fruit will accomplish this during the first four weeks of bloom. As the season progresses, the percentage of bolls set after this time is reduced. On several occasions, I have tagged bolls on the 15th of August and gone back to the field about 3 weeks later. It was rare to find more that 3-4 bolls set on the 100 blooms.
To get a clearer picture of what is happening this year and why things are earlier than normal; we need to look at the DD-60 or heat unit data from the weather stations. The temperatures are the primary driver of cotton development. At Portageville, the heat units from May 1 through July 15 were 1322. This was the most heat units in this time frame in the last 8 years. If we look at May 1 through August 1, we had 1709, which is also the most heat units during the past eight years. Even if we did not get any additional heat units between now and August 15, we would still exceed four of the last eight years. For the May 1-September 1 time frame, the 1709 would still exceed the 1673 that had accumulated in 2008.
According to data collected at the Delta Center, we normally will have heat units in the range of 2,150-2,300 around September 21 or later. I think that it's safe to predict that we will exceed this range this year.
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Dr. Michael R. Milam is an agronomy specialist and county program director with University of Missouri Extension in Dunklin County.