Prepared by the CSD Extension and Development Team.

Key takeaways

• To achieve optimal cotton yields it is crucial to strike a balance between vegetative and reproductive growth.
• While growth regulators won’t increase yield potential, it can help the crop fulfill its potential by preventing excessive vegetative growth and promoting balanced development.

 

Monitoring growth and determining the need for growth regulators

Various measurements including plant height, main stem node growth rate, nodes above white flower (NAWF) and internode distance are used to capture vegetative growth. These measurements indicate Vegetative Growth Rate (VGR) and should be taken weekly for an accurate assessment.

Focus on the top five internodes as the most important indicator for determining the need for a growth regulator.

Pay close attention to the VGR. If exceeding 5.5 cm per node, this may indicate a need for growth regulators application. Consider the following.

• Different cotton varieties exhibit varying responsiveness to growth regulators. A moderately responsive variety might indicate a need for higher rate applications at a VGR, while a weakly responsive variety might only require it at minimal amount.
• Field history, fruit retention, and environmental factors like upcoming growing conditions, chance of stress, crop moisture levels, and temperature.

 

Application Timing and Rates

Apply growth regulators at the 8 to 10 nodes (match-head square) stage for aggressive growth, especially if there’s a history of rank growth, high nitrogen application and/or early rainfall.

The early-season application of growth regulators can be particularly beneficial for shorter-season growing regions, potentially improving yield. However excessive or mistimed applications can negatively impact yield.

Avoid applying growth regulators when the cotton plant is stressed, as this can exacerbate the negative effects.

Base your decision on various factors such as field history, varietal response, and predicted outlook for growth conditions.

Consider lower rates for less vigorous crops and higher rates for rapidly growing crops. If the Height to Node Ratio (HNR) trends high or exceeds the upper thresholds, growth regulator application is likely necessary. For more on this topic, see the blog article Monitoring for cotton plant growth regulation.

Specific Application Strategies

Research suggests that application of early-season growth regulators, whether at high or low rates, generally don’t significantly impact yield in longer-season regions. However, there may be potential yield benefits in shorter-season regions.

Studies also indicate that very high early-season growth regulator rates can lead to yield reductions.

Additional Considerations

Regularly monitor HNR and fruit retention to guide growth regulator application decisions. CSD’s CottonTracka™ has now included a Vegetative Growth Rate display for each crop inputted. Visit csd.net.au/trackwithcottontracka.

Irrigate after growth regulator applications if possible, as this can encourage growth.

Summary

Optimising cotton management with growth regulators involves a multi-faceted approach.

Closely monitor crop growth, consider varietal and environmental factors, apply growth regulators strategically and adjust rates and timing as needed. This will help manage vegetative growth effectively, promote balanced development and ultimately contribute to achieving optimal yield.