The Bloom Period
Keith Edmisten - Cotton Extension Specialist
Charles Burmester - Extension Agronomist
The following Cotton Note was written in Alabama prior to Keith Edmisten coming to NC State to accept the Cotton Specialist position. This was called:
Plant monitoring techniques such as nodes above white bloom and plant mapping have received a great deal of attention in the past few years. These techniques require a certain amount of time and energy but can tell us a lot about our cotton crop and how the crop should be managed. This article is the third in a series of discussions concerning plant monitoring.
The Bloom Period
Cotton normally blooms for a period of seven or eight weeks. Stresses such as drought, nematodes and/or fertility can shorten the bloom period significantly. The bloom period can also be lengthened by poor fruit retention and/or excess nitrogen (with adequate rainfall). Plant mapping as discussed in Plant monitoring: 2. can be beneficial during the bloom period. In addition, monitoring the movement of first position white blooms up the stalk during the bloom period gives us a good idea of the condition of the crop.
Nodes Above White Bloom (NAWB)
Counting the nodes above white bloom is a relatively easy observation to make during the bloom period. This technique involves locating the highest first position white bloom on a plant and counting the nodes above that bloom. Each node above the highest first position first bloom should be counted if the main stem leaf associated with the node is larger than a quarter. Chart 1 illustrates how this count should be made.
Implications of Nodes Above White Bloom (NAWB)
NAWB should be 8 to 10 at first bloom depending on variety and growing conditions. NAWB at first bloom for short season varieties that fruit on the 5th to 6th node normally will be at the lower end of this range while full season varieties will usually be at the higher end of this range. Stress due to drought or nitrogen deficiency will result in a lower NAWB at first bloom. Poor fruit retention and\or excess nitrogen may result in a higher NAWB at first bloom. NAWB should begin to decrease after 2 weeks of bloom due to fruit load. If NAWB does not begin to decrease during the third week of bloom fruit retention and boll size should be evaluated. Crops with a large NAWB may be suffering from poor fruit retention due to insect damage. Under these situations the crop will grow rank if ample moisture and nutrients are available. In crops with higher than normal NAWB at first bloom and/or crops where NAWB does not begin to decrease during the third week of bloom one can expect a strong response to Pix. On the other hand, Pix may not be needed in crops with low NAWB at first bloom and/or crops where NAWB decreases rapidly during the bloom period.
NAWB should continue to decrease through the remainder of the bloom period as the plant moves towards "flowering out the top". If NAWB is decreasing to rapidly one should attempt to identify stresses and alleviate them if possible. The most common stresses that will cause a rapid decrease in NAWB are drought and nitrogen deficiency. When nodes NAWB is lower than normal at first bloom and or decreases more rapidly during bloom than desired due to drought stress increasing the frequency of irrigation may be beneficial. Foliar urea applications have been shown to increase NAWB and yield where NAWB is lower than desired due to nitrogen deficiency.
When NAWB has reached 5 the terminal has essentially ceased growth and cutout is eminent. Less than 2 percent of the yield is set after NAWB reaches 4. Cutout occurs when NAWB reaches 3 or less.
Whenever NAWB is higher than normal - look hard at insect related fruit shed and consider Pix to control plant height.
Whenever NAWB is lower than desired - avoid Pix use and attempt to alleviate any drought or nutrient deficiencies.
Back to the 1997 and earlier Cotton Notes
Carolina Cotton Notes CCN-92-6a June, 1992