There is no such thing as a "cal-mag" deficiency...
Hey Guys, I took this from another website because i found in interesting and informative. There's some good points in here and i'm often quick to diagnose cal-mag def rather than cal or mag def.
Thread title pretty much says it all. Use the charts in my signature line to help with understanding, but the gist of it is this: Calcium (Ca) and magnesium (Mg) are two different elements required for plant nutrition. One, Ca, is immobile. That means it cannot be translocated (moved) through plant tissues. The other, Mg, is highly mobile in plant tissues.
Understanding this is important on a few levels, including making a proper diagnosis. Because Ca is immobile a deficiency will only occur on the upper, or newer growth. Because Mg is so mobile deficiencies occur on the older, or lower growth.
Their appearances and effects are also very different, and while both elements play together and are required by the plant, they cannot be lumped together as a single deficiency. You can experience both a Ca- and a Mg-, but they are not one and the same thing, not at all.
This is one of the charts posted in my thread, and while it is very good it does have a mistake--calcium is immobile. Keep that in mind.
BOTH Ca and Mg can be delivered into plant tissues via foliar applications to help correct, however, while the Mg- signs prior to actual necrosis can be alleviated and even reversed, the same cannot be said of Ca-.