Molybdenum deficiencies are quite uncommon, but they do have a higher incidence in marijuana strains that change colors in cold temperatures. The symptoms will start with middle leaves that turn yellow. The signs of the deficiency will move toward the shoots and younger leaves as they become twisted and curled.
Leaves will turn pale and have a fringed or scorched look. Their growth will also slow or look strange. Older leaves that have experienced chlorosis will have rolled margins, slowed growth, and tips that curl inward and are red.
It's not uncommon to falsely think that a molybdenum deficiency is actually a nitrogen deficiency. But, molybdenum affects the middle of the marijuana plant and then moves up (making it extremely mobile) while nitrogen starts out at the bottom.
By contrast, an excess of molybdenum may resemble an iron or copper deficiency. Molybdenum primarily works from within enzymes to help transform nitrates into ammonia. The ammonia is important for protein production, making molybdenum rather essential.
Obviously, it's important to stop a molybdenum deficiency before it even starts. Products like Marijuana Booster will certainly help with that endeavor. You may also want to use a foliar spray composed of water-soluble fertilizers. To avoid over-fertilization, use a small amount of a hydroponic micronutrient mix for this task. You can use them as foliar sprays or apply them directly to the soil.
For the most part, you're going to find a lack of molybdenum when there's also a lack of sulfur and phosphorus. By contrast, a molybdenum surplus won't do much damage to the marijuana plant, but it can be harmful to humans if ingested in large quantities.