Ferris 5000/61RCE Operator's Manual page 51

Stingers
Stingers are sparse patches of uncut grass left behind
the mower. Stingers are usually caused by operator
error or poor blade maintenance.
CAUSE
Blades are not sharp or are nicked
Blades are worn down too far
Engine speed is too slow
Ground speed is too fast
Deck is plugged with grass
Lawn Care & Mowing Information
SOLUTION
Sharpen your blades
Replace your blades
Always mow at full throttle
Slow down
Clean out the mower
LC-7