Maybe it is too much water. I water mine once a week in spring and fall, and twice a week in the summer--and that's in 40+ deg. C temps! Unless the soil is extremely fast draining, every-other-day watering is likely to damage the roots. Hmmm. I just realized: I am assuming that these are in the ground, not in pots.

Just so you know, Hannes, you can reply in the answers box of the original question, and I and anyone else who commented will automatically be notified.

Been a while. yes they are in the ground. Over the last month I have planted a couple more trees and have moved the sick chilli tree to a big pot. As you have mentioned it might be to much water. My other plants are looking strong though. I will add some picks of the sick tree

I just realized that I am making another assumption. I'm assuming that these are big chili pepper plants! Is there a kind of actual tree called a "Chilli"?