Eucalyptus Trees: Leaves turn yellow and trees die.

We plant eucalyptus trees in India every three years they are harvested and new ones are planted. New trees are generally planted at the end of summer. (The weather is hot and extremely humid). If the region gets a lot of rain showers at least 10% of the trees develop a condition.
The tips of leaves turn dry (brown). The tree's growth slows down. All new leaves that come out are a yellow color and eventually the trees start having red leaves.
It is interesting that the leaves that grew initially are still green. This spreads to other nearby trees if the infected tree is not uprooted and burnt at an early stage.
Could somebody explain why this happens and what can be done to prevent it?
We also have termites from time to time. Could someone suggest a prevention/cure for that too?
Thx, X
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