This month we will look at cotton crop water use from first flower through to peak flowering and then cut out and monitoring crop growth and fruit retention
Welcome to this January edition of the Newsletter, the first for 2026. This month we will look at cotton crop water use from first flower through to peak flowering and then cut out and monitoring crop growth and fruit retention.
January is a critical time for crop management. Monitor first position fruit retention, whether it is the top 5 nodes or the whole plant. CSD uses the whole plant first position retention as a standard. Monitor crop growth rates to help with plant growth regulator application decisions if needed. Measuring crop growth rates and fruit retention helps with managing the crop better.
Cotton crop water use after flowering starts
Cotton plants have significant water requirements after flowering commences. Understanding these patterns is crucial for effective irrigation management and maximising yield potential.
Peak Water use period
The daily water use of cotton plants reaches its peak during late flowering, typically in late January in Australian growing conditions. During this critical period includes the below.
Early season water use: 2-4 mm per day
Peak water use (late January): 8-10 mm per day
Post-flowering decline (March): approximately 5 mm per day
During Active Flowering
Cotton is most susceptible to water stress during a 50-day period from first flower to approximately 10 days after cut-out. During this time:
Water stress must be avoided, as yield losses can reach 2.7% per day of stress when fruit retention is high.
Most frequent irrigation is required during the flowering period.
Timing is most critical for crops flowering in February-March when evaporation rates and crop sensitivity to moisture stress are highest.
Water stress is most likely when plant available soil water falls below 50%.
Management Recommendations
To optimise yield and quality after flowering:
Schedule irrigations to maintain plant available soil water above 50%
Plan for one or two irrigations between cutout and final irrigation, depending on soil type and rooting depth
Avoid waterlogging, which can cause yield reductions of 0.2 bales/ha per day during flowering
Monitor soil moisture levels closely rather than relying solely on visual indicators of stress.
More information about water scheduling and water budgets can be found on the CSD Website under ‘Irrigation IQ™’, (formerly called The Water Dashboard). Irrigation IQ™ is a joint venture between CSD, the CRDC and Goanna Ag.
It offers a whole irrigation knowledge package including:
irrigation timing and real time monitoring
planning and forecasting for water use and getting through the peak demand times
traceability and tracking water from source to field.
Figures 1 and 2 are examples of the information that can help farm managers to manage water on farms using Irrigation IQ™.
Managing crop vegetative growth rate (VGR)
The Vegetative Growth Rate (VGR) is a key measurement tool used to monitor cotton crop vigour and inform growth management decisions. Here's the formula and how to use it.
The VGR Formula
VGR (cm/node) = (this week's height - last week's height) ÷ (this week's nodes - last week's nodes)
Where:
Height is measured in centimetres from the ground to the growing point of the main stem (not to the end of the top leaf)
Nodes are counted from the cotyledons (numbered 0) to the top node with a fully unfurled leaf
Measurement Protocol
To accurately calculate VGR:
Measure plant height from ground to the growing point of the main stem
Count total nodes from cotyledons to the top node with a fully unfurled leaf
Record measurements on at least 20 randomly chosen plants
Repeat the same procedure one week later
Apply the VGR formula to calculate the rate of internode increase
When to Monitor VGR
Start: Before first flower, around 10-12 mainstem nodes
Continue: Until mid-flowering, as rapid increases in growth rate can occur at any time during this period.
Interpreting VGR Values
VGR > 5.5: May indicate the need for mepiquat chloride (MC) application.
VGR > 7.5: May indicate a definite need for a MC application
However, VGR measurements should be considered alongside other factors includincrop variety, fruit retention levels, field history, climatic conditions, and soil type before making management decisions.
What's on?
A Field Walk at the Jedburgh, Warren CSD variety trial in conjunction with CGS Warren will be held on Tuesday January 20th in the morning. Keep an eye out for the invitation.
