Basil likes at least 6 hours of sunlight, and temperatures of about 70F in the day and at least 50F at night. If your area has been experiencing colder temperatures, it could be that your basil has cold or frost damage. It may also be sunscald, which can occur when sunlight is too intense on tender vegetation, especially wet leaves. This may happen if the basil was not hardened off before transplanting outside in the cooler temperatures. To harden off, you'd put the plant out in a sheltered area for an hour or two one day, increase the amount of time a bit the next day, and so on, as well as later moving it to positions closer to the full-sunlight conditions of its permanent home to-be; do this for about 10 days. Without hardening off, your plant is more susceptible to sunscald and other cultural problems. If you think it might be sunscald, cover the plant in a row cover material or shade cloth for a few days to see if the reduced sunlight might be helping it to recover. If you think it is a disease, you might want to remove the affected leaves (unless it would strip off too many), and monitor the plant.
Sunscald can appear as paper thin silver to pale brown spots on leaves (or fruit). Here is a photo of sunscald on a greenhouse basil plant (I don't think the pink color in this photo is usual):
Basil likes at least 6 hours of sunlight, and temperatures of about 70F in the day and at least 50F at night. If your area has been experiencing colder temperatures, it could be that your basil has cold or frost damage. It may also be sunscald, which can occur when sunlight is too intense on tender vegetation, especially wet leaves. This may happen if the basil was not hardened off before transplanting outside in the cooler temperatures. To harden off, you'd put the plant out in a sheltered area for an hour or two one day, increase the amount of time a bit the next day, and so on, as well as later moving it to positions closer to the full-sunlight conditions of its permanent home to-be; do this for about 10 days. Without hardening off, your plant is more susceptible to sunscald and other cultural problems. If you think it might be sunscald, cover the plant in a row cover material or shade cloth for a few days to see if the reduced sunlight might be helping it to recover. If you think it is a disease, you might want to remove the affected leaves (unless it would strip off too many), and monitor the plant.
Sunscald can appear as paper thin silver to pale brown spots on leaves (or fruit). Here is a photo of sunscald on a greenhouse basil plant (I don't think the pink color in this photo is usual):
http://negreenhouseupdate.info/photos/sunscald-basil-foliage
If you think that it is a disease, you might check out this page:
http://plantclinic.cornell.edu/factsheets/basildiseases.pdf
Some insects can also cause papery thin spots or tiny holes when they feed, such as sawflies, flea beetles, or leafhoppers.