Hello. My cauliflower was growing well and then one of the plants started to get gray discoloration at the tips of the older leaves. This rapidly spread throughout the leaf and the leaf becomes grey and crumbly and dry. The veins are largely unaffected. This has only happened in the outer, older leaves thus far.
I have looked for insects and have not seen any. The plants are on my rooftop in a container. The other cauliflower and broccoli plants in this container are growing well without signs of disease.
I was thinking this is a nutritional issue, but I'm not sure. I did add garden lime to my potting mix when I planted it. Thank you!