Where are you located Tam? Depending on the weather this could be just sun burn or wind damage as well.

The speckles could be sucking pest damage, look with a magnifier. The chewing is insect damage such as caterpillars. The blackening, associated deformity could be bacterial blight. Or maybe a problem with chemicals or minerals in irrigation water - especially since in the one instance it was concentrated at the leaf tip, where water would tend to accumulate.

It could be a mixture of all the above things Tam. Try moving it to a shaded area to see if it helps. Try not to fertilize the plant on an extremely hot day as well. My plants reacted badly when I did that very early in my gardening days. It blackened the tips of the plants the same way. If its only one leaf don't worry too much. The leaf will die but the plant will be ok. But if its any other issue like Embothrium mentioned just keep a watch to see if it spreads. If you see it increasing maybe a diluted neem spray might help.

I have found spider mites and salt deposits in the soil to do that and not enough warm air movement..