WHY IS THERE NO FRUIT ON MY MANGO?

(One of a series of articles about growing fruit trees in Samoa, written by Digby Gotts and published in the 'Samoa Observer' between December 2000 and April 2001)

Many mangos in Samoa have no fruit at this time of year for one of several reasons. Firstly the soil here is very rich, and unless the tree is stressed by cold or dry conditions, this will keep the tree producing leaves instead of flowers and so no fruit can even start. Then if your mango does produce flowers, many of these will be killed by a very common fungus (anthracnose) that is encouraged by the warm and wet climate. You can recognise the fungus by the black spots appearing on the leaves . This fungus can also cause small fruit to drop off the tree and can cause even large fruits to be split open before they mature.

You can help your mango tree resist the fungus by cutting out any branches going straight up in the middle of the tree and removing any other trees that are touching the mango. Both of these actions will increase the amount of sun and wind into the mango tree and so help it to dry out, killing the fungus. Only ever cut branches off your mango at Christmas time, as cutting branches will also force the tree to make new leaves and will block it from making flowers.

There are also chemical sprays available, based on copper solutions, which can also help control the fungus. These can be very expensive, as they have to be applied at least every 2 weeks or every time it rains for the flowering time! Opening up your tree to sun and wind is a lot cheaper.

Some mango varieties are resistant to anthracnose and these can be a better choice than seedling trees for at least this reason. Resistant varieties available at Nafanua include Golek, Nam Doc Mai and Zillate. Also available are local varieties such as Tilafono, Lautasi, Atipera, Parrot, Ireta and Manulagi which have been selected for their good fruit and their ability to survive in Samoa.

Only use fertiliser on the tree if it is turning a pale green to yellow in colour. I see trees like this usually near the beach, where the sandy soil has lost its nutrients to the rain. If you do you use fertiliser on the tree, only ever do so at Christmas or when you are picking fruit. Used later in the year this fertiliser will be enough to also force the tree back into producing leaves instead of flowers.

If your tree is at least 8 years old and still hasn't flowered, then one possible trick to do before the end of January is to cut off every branch where it is about 3 inches wide, leaving no leaves on the tree at all. Take away all the leaves and small branches and leave the tree to grow a new set of leaves. This will help reduce the nutrient available and will put stress on the tree helping it to flower next season. Every Christmas, give your tree a haircut, keeping its size down to one where you can reach all the fruit.