From the HORT402 manual
Bright yellow interveinal chlorotic lesions are typical of magnesium deficiency. These lesions may also have a violet tinge in some species. Older leaves are usually affected first, but sometimes if Mg withdrawal from older leaves is too slow, younger leaves may also show deficiency symptoms.
- Interveinal chlorosis of the older leaves
- Magnesium is the central atom in chlorophyll giving it its green color