Deleafing Banana Plants to Control Sigatoka

Zeki Murad, Department of Primary Industries and Fisheries. 

Deleafing is the main activity for controlling the spread of yellow and black Sigatoka. Deleafing keeps the development of necrotic patches on leaves in check, thereby reducing the number of ascospores that can be emitted by the diseases. Chemical sprays and oil only work on the early stages of the disease on and in the leaf depending on the chemical. Once a spot turns dark there is no chemical or oil that will stop its development. It will go on to form large dead patches on the leaf that will emit lots of spores to continue the cycles of infection. They only way to break up the cycle is by deleafing.

Leaf area is essential for photosynthesis in the plant. By deleafing we reduce the area available and as a consequence the development of the bunch can slow and towards harvest the bunch can try to ripen prematurely. This can lead to "mixed ripes" at the ripening centres. This is where some of the bananas in a box turn yellow faster than others because the plant they came from was stressed and tried to ripen the bananas too soon.

To avoid this situation it is important to deleaf regularly to keep the number of spores in the air to a minimum. It is also important to only remove leaf area where there are sigatoka infections. There is no use taking of the bottom two leaves without thinking about the task, when the leaves remaining on the plants still have sigatoka spots! Growers should make sure their workers or contractors staff are aware of this and that the job is being done properly otherwise they are wasting their money.

Remember to examine suckers also. Some growers have confused cordana with leaf spot so if in doubt remove the spots. Also it is worth noting that cordana infects through sigatoka infections and often masks a sigatoka leaf spot that can cause reinfection.

It is important to deleaf conscientiously removing all spots where they are found and on whatever leaf. To do this right deleafing cannot be done in the evening or at night, as it is impossible to remove leaf spot properly. If a leaf only has a few spots on it at one end then remove the leaf area only at that end. If only the end half of the leaf is covered in spots then remove that end only and leave the other half attached to the plant. (see figure 1).

Figure 4. Remove all leaves with leaf spot. Here at least three leaves
have leaf spot. Do not remove only the bottom two leaves. All areas
with leaf spot should be removed regularly.

Tools

By choosing the correct deleafing tools the task can be made easier and therefore quicker and more efficient. Knives and blades should be sharp and long enough to move leaves aside to look for leaf spot and to cut pieces of leaf from the highest leaves if need be.

Curved knives tend to only allow a downward chopping action and it is more efficient to have a knife with both sides sharpened to allow upward cutting motions as well as downwards cutting. Vertical blades give good flexibility also. The pole must be long enough and light to allow fast and efficient cutting.

Figure 5. A traditional deleafing blade where only
the lower surface is sharpened. This limits
cutting motions in the paddock slows down the
work and costs more.

Figure 6. A blade with both the upper and lower
surfaces sharpened gives more flexibility when
deleafing and therefore adds speed to the task.

Last reviewed April 2005