"The most common turf response to inadequate Mn is a markedly reduced growth rate of both shoots and roots....

Increased disease incidence is another symptom of Mn deficiency. Because Mn plays many critical roles in the biosynthesis of phenolics and lignin, grasses deficient in Mn are unable to respond to pathogen attack by producing phytoalexins that would inhibit spore germination and block fungal invasion"

Richard Hull, University Rhode Island, Turfgrass Trends 2001

A note from the field with real-world experience regarding the importance of Manganese

"This summer was a real good test. I did not have any Summer Patch when I heard it was going around and I have not sprayed any fungicides in four years to prevent it. I still spray fungicides but not for Summer Patch.

What works for me is spraying two jugs of Defense-Man per acre with some Pervade (1.0-1.5 oz/1,000) and water in with two turns of the over heads. The spray tank is set up to spray 1.5 gallons water / 1,000 or 66 gallons / acre. I spray this three weeks apart starting in June." 

Floratine's Defense-Man is a concentrated 25% manganese organic acid chelate (i.e. NOT EDTA chelate per reference above) that also contains micronized humic acid powder. The organic chelation ensures rapid plant availability and encourages microbial proliferation in the soil. Uniquely packaged as a dry powder in one-gallon plastic mixing jug- just add water, shake and pour into the sprayer.