I suppose it could be a Ca deficiency; early onset. I assume you're growing in soil(?). Then why only 4 of 16 if they're all getting the same of everything?? Before you dump "panic" nutes, check your water pH and soil pH on the regular. Bad pH can really upset nutrient uptake. Your soil might already have what it needs for the grow to thrive, but a possible pH issue will never allow the plants to get what they need from the soil. My well here in WA. is 8.5 so I pH down to about 6.4-6.5 before I water, every watering. My soil sits at a consistent 6.9-7.0 pH. No nutrition issues ever, from seed to take down.
I would seriously inspect all your plants for what may be a pest outbreak. Use a magnifying glass if need be. Look for tiny bugs, eggs or egg cases and pest skin molts; especially under the affected and larger non-affected leaves.
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I suppose it could be a Ca deficiency; early onset. I assume you're growing in soil(?). Then why only 4 of 16 if they're all getting the same of everything?? Before you dump "panic" nutes, check your water pH and soil pH on the regular. Bad pH can really upset nutrient uptake. Your soil might already have what it needs for the grow to thrive, but a possible pH issue will never allow the plants to get what they need from the soil. My well here in WA. is 8.5 so I pH down to about 6.4-6.5 before I water, every watering. My soil sits at a consistent 6.9-7.0 pH. No nutrition issues ever, from seed to take down.
I would seriously inspect all your plants for what may be a pest outbreak. Use a magnifying glass if need be. Look for tiny bugs, eggs or egg cases and pest skin molts; especially under the affected and larger non-affected leaves.
PEACE!