Last week I hosted a Cotton Workshop that focused on the phase of cotton growth from first square to first bloom, the current stage of our cotton crop. Since this growth stage is so important, I thought I would review some basic cotton physiology as it relates to current growing conditions.
Here are some important pointers to consider when managing cotton during this growing stage. Currently the heat units for our cotton crop are very near normal and early planted cotton is at least at the six to seven node stage and setting squares. This cotton should be at first bloom by the first week of June. As a general rule, for every 50 heat units accumulated, the cotton plant will produce a new node.
Moreover, at this time the cotton plant is continuing to develop an extensive root system and will do so until about one week after flowering.
It is important to note that up to 85 percent of the lint yield will be determined by first bloom, and up to 80 percent of that yield will come from the first fruiting positions on the cotton plant. So now is the time to see that our cotton has optimum growing conditions and we need to protect that first fruiting position.
Cotton insects during this growth stage that warrant serious considerations include cotton fleahoppers at which the treatment threshold is 15 per 100 terminals. In addition, aphids can also cause problems, and if more than 50 aphids per leaf persist for more than seven days treatment for them is probably warranted.
One of the goals during this growing stage should also be to develop the best plant structure possible. To achieve that, we need to consider the growth potential of the plant. Ultimately the, final cotton plant height here in the Coastal Bend should be 30 to 35 inches for 30-inch rows, or a rule-of-thumb used to predict optimum plant height is to multiply the row width times 1.1. With these limits, one can ensure that row middles are covered but not to such a degree that boll rot will develop.
The cotton plant produces a new node in the terminal every three days. Each new internode continues to extend and thicken over the next 12 to 15 days, depending on temperature and growing conditions. The most rapid expansion (85 percent) occurs in the first six to ten days. Heavy rains or use of irrigation will cause cotton to increase nitrogen uptake, which can result in rapid growth.
A cotton plant will do a good job of regulating its own height if there is a lack of heavy rainfall and the presence of a heavy fruit load during this time.
To help control rapid growth the product Mepiquat chloride (MC) is used. MC will help retard excessive plant height as it suppresses stem elongation of newly formed internodes. The minimum MC concentration in the plant necessary to provide a maximum level of reduction is 12-15 parts per million. It is extremely important to make the first applications of MC early enough, usually around Matchhead Square to keep the plant’s growth under control. For more information about using MC to manage cotton plant height consult the publication found at this web site; http://safiles.tamu.edu/agronomy/cotton/b6042.pdf
So at the conclusion of this growth stage that is first bloom, one can count the nodes above white flower (NAWF) to determine just how well the crop is doing. In fact, we would like to see that number around eight or nine nodes. If that number is at five, the cotton plant is in trouble and production of additional squares will end as this is known as “cut out.” If the plant has nine NAWF at first bloom, this is an indicator that the plant has a lot of “horse power” and great yield potential. So we hope around June 10 our cotton plants have eight or nine NAWF, and of course a little more rain between now and then will help achieve that goal.