Cotton Defoliation Pointers

05 March, 2007

Timing of the first defoliation of cotton crops is regarded as crucial in terms of fibre quality. Too early presents potential quality problems, while too late can make the crop vulnerable to adverse harvesting weather.

CSD extension and development agronomist, Rob Eveleigh, told the weekly Web on Wednesday video that traditionally, when a crop gets to around that 60 per cent open, the crop is getting close to being ready to defoliate.

Alternatively, when there are around 3 to 4 nodes above cracked boll we can certainly look at safely defoliating that crop.

“Another method involves picking bolls off the uppermost harvestable fruiting branches and cutting those bolls with a sharp knife and looking into them to see whether the seed coat is mature.

“If there is no gelatin in those seeds, and you have got a nice firm brown seed coat, then the boll is physiologically mature. If 98 per cent of the bolls are mature then certainly there are no problems beginning the defoliation process,” he said.

He noted, however, that in seasons when crops suffer from water stress and a lack of water to finish the crop, different defoliation methods should be considered.

“Generally, you have to increase the rate by 20 per cent or more than you would be using on a fully irrigated crop that’s ready to defoliate.

“The other thing to keep in mind is that often the cuticle thickens up a little bit more so you have got a little bit more wax on the outside of the leaf.

“Sometimes it is a little bit more difficult to get the material into the leaf to get that defoliation action occurring, so it is important that you use a good quality oil and certainly keep the rates of the oil up to the recommended levels to make sure that you get the product into the leaves.

“Other than that there is not a lot you can really do. It’s a question of using robust rates on the first few fields and then modifying your rates accordingly,” Rob Eveleigh said.

Further information: Rob Eveleigh 0427 915 921