Plant monitoring (or mapping) provides a system to evaluate the growth and development of cotton plants throughout the season. You can use this information to fine tune management practices for the current crop stage. Many pest management decisions must be made at specific growth stages, and plant mapping helps you time them precisely. Plant measurements and calculations for making management decisions change as the plant develops.
Early Squaring
Plant monitoring during early squaring focuses on plant vigor and square retention. Measure:
- Plant height.
- Total number of mainstem nodes.
- The first position squares on the terminal 5 fruiting branches.
For more information about making these measurements and for recording forms, ask your local farm advisor. You can also check the UCCE Cotton Production Information site for details on how to apply monitoring information for: plant growth regulator applications, lygus treatments, and irrigation decisions.
Early Flowering to Preharvest
Mapping plant growth from early flowering to preharvest consists of tracking:
- Retention of squares in the bottom and top first position fruiting branches.
- The number of nodes above white flower.
- The number of nodes above the highest cracked boll.
Monitoring Square Retention
Square retention is evaluated in the San Joaquin Valley to help determine the need for lygus bug management. Track the percent retention of the first-position squares on the top five and bottom five fruiting branches and keep records .
Start at early squaring:
- Examine five top branches and five bottom branches on each of five plants in four areas of your field.
- On each branch check for the presence or absence of first-position squares.
- Use the diagram of the cotton plant to help you.
- After the plant has developed more than ten fruiting branches, stop counting fruit on the bottom five branches if the average boll retention remains constant for 2 weeks in a row. You can use this retention level for the rest of the season.
Treatment may be warranted if you find 3 to 6 lygus per 50 sweeps before bloom and the square retention is lower than expected.
After monitoring for fruit retention, use the square and fruit retention action threshold table to look up the critical square retention based on the total number of fruiting branches and the percent fruit retention on the bottom five fruiting branches.
Monitoring Nodes above White Flower
The primary use of measuring Nodes Above the White Flower (NAWF) is to determine when cutout occurs. Cutout is reached when 95% of the cotton bolls are mature and have advanced beyond the presence of squares and blooms. There is also no new terminal growth. Cutout indicates that 95% of the crop has been set. Stop sampling for lygus bugs at cutout since bolls are generally not susceptible to lygus bug damage 10 days after flowering.
Measuring NAWF:
- Select a minimum of 5 plants with a first-position flower from each of four different areas in the field.
- Count the node with a first-position flower as zero and move toward the terminal.
- Record the total nodes above white flower for all of the samples.
- Record the number of plants sampled.
- Divide the total number of nodes by the total number of plants sampled.
If the terminal node has a leaf associated with it of at least 1 inch in diameter, consider it a new node.
Monitoring Nodes above Cracked Boll
The average number of nodes above the cracked boll (NACB) provides a measure for defoliation timing, taking into account not only the potential yield loss but also the loss of fiber quality in immature bolls. Ideal timing for defoliation occurs when unopened harvestable bolls are an average of four or less nodes (including missing branches) above the highest first position cracked boll. If it becomes necessary to defoliate a field prematurely at an average of 5 nodes above cracked boll because of a honeydew-producing insect infestation, a yield loss of less than 1% will occur; at 6 nodes above cracked boll the loss will be less than 2%.
The number of nodes above the first cracked boll helps you determine the proper time to apply defoliants. Select 5 random plants from each of four representative areas of each field for a total of 20 plants. Choose plants that have a cracked boll on a first position fruiting branch. Use the cotton diagram to help locate the various parts. Find the uppermost cracked first position boll and count this as fruiting branch zero. Count the number of nodes above the fruiting branch zero until you reach the most apical harvestable boll on the plant. This is a boll that is large enough and mature enough in development that it will open before the scheduled harvest date. The number of nodes you counted above fruiting branch zero is the NACB. Average this number for the 20 plant samples.
| A. | Total number of plants sampled ............................................................ | = | ___________ |
| B. | Total number of nodes above cracked boll ........................................... | = | ___________ |
| B ÷ A | = | ___________ |
You can use NACB to schedule your defoliation as follows:
- 4 NACB is used as a target for the first harvest aid in Upland/Acala
- 3 NACB is used as a target for defoliant timing in Pima