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Cotton

Monitor Nodes Above Cracked Boll

The average number of nodes above the cracked boll (NACB) helps you determine the proper time to apply defoliants, taking into account the potential yield loss and the quality loss from immature bolls. Ideal timing for defoliation is 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, for instance, because of honeydew-producing insect infestation,

• At an average of 5 NACB, a yield loss of less than 1% will occur.
• At 6 NACB, the loss will be less than 2%.

How to monitor NACB:

1. Select 5 random plants from 4 representative areas of each field for a total of 20 plants.
   • Choose plants that have a cracked boll on a first position fruiting branch.
   • Refer to the cotton anatomy diagram to help locate the various nodes and branches.
2. Find the uppermost cracked first-position boll and count this as fruiting branch zero.
3. 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 counted above fruiting branch zero is the NACB.
4. Take the average this number across the 20 plant samples.

These are the number of nodes above the highest cracked boll. You can use NACB to schedule your defoliation.

• For Upland/Acala, 4 NACB is the target for the first harvest aid.
• For Pima, 3 NACB is the target for defoliant timing.

Related information

• Cotton plant diagram
• UCCE cotton defoliation and harvest aid recommendations
• Yield loss for defoliating at various nodes above cracked boll
• Schedule defoliation