Gday Everyone i need urgent advice

[Beauthenewbiegrower]

Hello everyone im new to this forum, i have recently got myself involved in growing vegetables an fruits.
I need some advice to what is happening with my vegtables.
I had thai basil that is now dead after it lost all its leaves, the leaves became black an it was just a trunk in the end.
The same is happening with my chilli tree, capsicum tree and my lemon tree also, there all about 3-4 months old.
I water regulary, liquid fertilize every fortnight, and use a bug spray to repel insects. After all this extensive care my plants are still dying, my tomatoe tree suffered the same fate also.
Any advice would be appreciated
Beau

 

[Chuck]

From the picture of the pepper and what little I could see of the plant, I would say the leaf drop is from overwatering and keeping the soil too wet.