Coat the bottom of the deck with oil, we use old motor oil. Then at the end of the day all that grass scrapes right off and the oil protects the deck from rust...it's a trick my wifes granpappy used in the cemetery back in the day.
It works on mulching decks as well. Some of us don't have the luxury of waiting until the grass is dry to mow. When the cemetery needs mown, we gotta mow it, dry or not. We switched to mulching decks and it keeps wet grass from blowing on the headstones which is nice.
Try the oil, it works.