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Fruit tree dieback, Palau

September 2015. A small farm on the east side of the island of Babeldaob, Palau, has land that is fairly well drained, with volcanic clay soil. The owner’s trees are showing dieback of branches, these include carambola, breadfruit, guava, mango, and mountain apple. Banana plants are also unhealthy: the main plants often die before bearing, or have only a small bunch.
Pineapple plants interplanted with banana seem relatively healthy, and the farmer said cassava, too, grew well previously.

The land was cleared from forest a few years ago, and the surrounding forest looks quite healthy. The betel nut trees are also healthy.

Leaves of breadfruit and carambola have what look like mines, or possibly surface feeding insect damage, and maybe small bagworms are present. There were no other insects on the trees. Young, partially expanded leaves look healthy and undamaged, but appear to be attacked after expansion. Shoot tips then die back, and the carambola trees eventually die back to the ground, then re-grow, only to die back again. The photos are representative of the symptoms shown by other trees.

It seems there are two things going on here; you have insects, possibly beetles, feeding on the surface of the leaves, and then something much more serious. But it would be good to know if the land was always under forest or whether it was farmeed some years ago. Is there a chance that it was a farm way back and that the soil has been contaminated.

What to do: (i) a soil test should be done; (ii) check the roots of bananas for nematode infection; and (iii) possibly trasfer the bananas to an area where bananas are growing well and plant them there.

Later (November 2015), the writer returned to the farm and found severe nematode infestation in the bananas and is using the recommendations given in an SPC flyer. As part of the management strategy the publication suggests applying crushed crab shells. It was also suggested that the bananas are pulled out and the pineapples are left to grow. Does anyone have any information on the susceptibility of pineapples to nematodes.

A member replied that surveys in done in Fiji, Kiribati, Samoa, Tonga and Niue by Orton Williams in 1980, found that Helicotylenchus dihystera, the spiral nematode, was the most common nematode associate with roots of pineapple, and there were other Helicotylenchus species, which were less abundant. Pratylenchus brachyurus numbers were generally low, and Pratylenchus coffeae, often found on banana in other countries, was not recorded on pineapple, and neither was Radopholus similis, which is also a major pathogen of banana.It was found only at one site in Samoa on pineapple, although it is common on banana there.

So from the surveys of those countries at least it seems that the major nematodes of banana, Pratylenchus coffeae and Radopholus similis, are not major pathogens on pineapple.

And what about the other trees?

Regarding the fruit trees, there are many weevils on the trees. Based on my inquiry to PestNet a couple of years ago (July 2013 – Crops/Fruitsnuts/Guava/Weevil%28CeleuthetesorLophothete%29,guava,Palau), could it be that the larvae of this weevil are feeding on the roots, and the adults are scraping the epidermis of the young leaves and twigs, and causing dieback?