Molybdenum(Mo) actually contains the proteins which help your marijuana plant take the Nitrogen(N) from the air. A deficiency leaves your plants with a pale and scorched look along with weird and retarded leaf growth. Towards the middle of the plant the leaves will start yellowing and the younger twisted up leaves eventually die. It's important to remember that this deficiency is usually present when Phosphorus(P) and Sulfur(S) are deficient as well.
This element will get locked out of soil at PH levels of below 6.4 and above 7.2. Below 5.5 and above 6 will also give a lockout in a hydro and soiless operation.
A cheap and easy fix for this is using something like a foliar spray Miracle Grow All Purpose Plant Food or Miracle Grow Tomato Plant Food. You can also use Peters All Purpose Plant Food which contains this micro element as well.
So now we take our drive down Highway 101 to see Nick because he has got his remedy right in the store. Nick has many organic solutions like Azomite which contains many micro nutrients. Azomite comes from a mine in Utah where a gazillion years ago a volcano erupted leaving a lake filled with volcanic ash. Over the last 30 million years, give or take a few, that lake bed evolved into a mineral that virtually contains every micro nutrient your plants could ever want. He also like a foliar spray made by Dyna-Gro called their Foliage Pro. This does great at giving a quicker effect to your marijuana which can also give you a peace of mind.
In San Luis Obispo at the Healthy Harvest store they recommend getting one of their fine micro-nutrient products which have small amounts of all the micros your plant could need including Sulfur(S). In particular they like the CNS17 from Botanicare. It works out real nice that as long as your plants aren't flowering it works as an excellent foliar feed so the results will show up much quicker. You can also use this as an additive to your water which works good too.