Ok,
I'm becoming a magnet for physiological disorders... mostly plant ones anyway. I suppose when plants are pushed to grow in a commercial setting, more chemical imbalances will be highlighted.
This is a problem that I've noticed among crassulaceae, particularly on Echeveria. Leaves become extremely brittle and crack at the slightest touch, like the epidermis looses elasticity and starts degrading. Sometimes the leaf will resemble alligator skin. This is accompanied by flecking (necrotic spots), and is followed by rapid death of the leaf. It starts on the eldest leaves, and progresses upward. Seemingly healthy plants can become riddled with symptoms in a matter of a week.
Prolonged cool weather (above freezing), and cold damp soil seem to predispose the plants. It has occurred every winter ( the southern California kind) on these types of plants. I've noticed the problem elsewhere during the cool season... it seems quite common and is sometimes fatal. Only once have I seen the problem on cold hardy types (agavoides, colorata, etc.), but mostly on gibbiflora hybrids and others from more southernly latitudes.
I had sent leaf samples to a lab for comparative nutrient analysis, but the results were murky. The occurrences don't seem consistent with a virus, and I've tried "infecting" healthy plants time and again with no success. In "Echeveria Cultivars", by Lorraine Schulz and Attila Kapitany, Dick Wright believes that a mycoplasma is responsible for similar symptoms. I think the problem is nutritional, and mostly likely involves nitrogen. Nitrification in soil, along with nitrogen transport and assimilation in the plant can be strongly hindered by cool damp soil and cool weather, respectively.
Has anyone else noticed this?
Any thoughts?
...I know there's at least 2% on this forum who care about crassulaceae
Matt