Question
I am growing basil... spread out in different location in my apx 1/2 acer market garden the plants were all started in doors at stagerd intervuls and planted at different times.some are now getting blacktips on the leaves Both older and younger plants  and the plants are not showing much growth ,which makes it unsuitable for market . I have lost a few plants to rot... the stem turns brown ,with some white mold the leaves fall off ... I am practicing organic methods. I was told that perhaps a folier spray with potasium might be helpfull .
Any words of wisdom and or suggestions would be appreciated  

Answer
Basil is very intolerant of poor air circulation and I have seen plantings get black tips after there has been a period of tempature inversion layers (hot, smoggy and humid )also what you are describing can be downey mildew. I would spray with a phosphite material(Monterey lawn and garden has a product called agri-phos)this product is safe to use but not organic. If you do want to stay organic you can try potassium bicarbonate which is organic(again try Monterey lawn and garden they have a product called bi-carb)this will work well on powdery mildew and just ok on downey mildew. good luck and thanks