Top 4 Cotton Defoliation Application Tips for Growers

It is that time of the year again when the Cotton is rapidly maturing and approaching defoliation.

I won’t get into defoliant rates or how to tell when to defoliate as there is plenty of literature out there describing how to achieve this including the CSD’s facts on Friday series. 

My main focus in this article is provide advice on how to maximise the performance of each defoliation application in order to minimise the chances of cotton fibre price discounts and, in some circumstances, lower the number of applications to one.

1. Use lots of water

Using a minimum of 100L of water per hectare ensures good coverage and consistency of application. I’ve noted on a number of occasions sub-par defoliations when lower rates of water have been used.

2. Slow Down

Every year, growers that have taken their time across the field have ended up with better results.

Slowing down to 10-12km/hr ensures that the chemical being used is evenly distributed across the canopy and any rocking of the Spray-rig’s boom due to uneven ground is limited.

3. Aim for a medium droplet size

Coverage is extremely important in achieving strong defoliation results. The importance of coverage is closely followed by decent penetration into the canopy. The medium size droplet (226 -325 microns) is the ideal size for providing coverage while still retaining a droplet size significant enough to penetrate deeper into the canopy. This penetration can be further improved while not limiting coverage too much by targeting the larger end of the medium droplet spectrum (closer to 325 microns than 226 microns).

4. Use a ground-rig for the first application.

A plane can often do a perfectly good defoliation job however from our experience ground-rig applications perform consistently better on average. In our experience, ground-rig applications tend to be more uniform and application coverage superior across the field. The importance of using a ground-rig decreases after the first application and defoliation from a plane for the second application performs close to, if not as well as a ground-rig application.

While there are many other elements that contribute to a good defoliation application, such as spraying under the correct weather conditions and avoiding applications before rain, I find that these three factors return the most significant results for our growers.


Written by

Robert Boulton

Black Earth Agronomy


The information provided above is based on experience based on the Darling Downs and may not necessarily apply in other valleys. There is also the chance that it does not apply to a growers specific circumstance so we recommend consulting your agronomist to ensure best performance on your own farm.

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