Well, not terminally ruined, as grass is very resilient, but if you leave them, the grass under each windfall will die, leaving small round bare patches. Also, in the short term, the dead apples will rot, attracting wasps, which can spoil an otherwise nice day in the garden. And dead apples go brown, with nasty rings of fungus pustules on them, uurgh, not very nice to look at.
Finally, the grass will grow over the apples, as you won't be able to mow there: if you try, the mower will bump and bang over the fresh windfalls, and will squash the older ones, thus worsening the "dead grass patches" problem.
So there is no alternative: if you have apples trees in your garden, and you value your lush green lawn, then you will need to pick them up.
However, help is at hand: I have invented an easy and cheap way to do it. You don't have to go out there every day, bending double to pick each apple individually.
Nor do you have to buy an expensive gadget for picking them up.
Or, you can look for devices to collect tennis balls - this fun little toy also costs £70 or so, and you can use it to pick up tennis balls AS WELL AS apples!
And here was me, not realising that my life was not complete, as I do not own a tennis ball collecting device....
Anyway, back to the plot, I can't quite get to grips with paying £70 or more for something that will only be used briefly once a year: but I don't want to break my back picking them up individually, so I generally just rake them up.
But this has drawbacks as well: it's frustratingly slow. The lightweight Spring Rake (which we mostly use in Autumn, ha ha, gardeners' joke) is too flimsy for heavy apples, but the solid Ground Rake tends to dig itself into the grass: it's hard work and slow, to rake up apples this way.
So I invented something better.
It's called the Apple Roller.
All you have to do is take an ordinary ground rake, stab one smallish apple onto each end, and lo! and behold, the rake glides across the ground as though it was on wheels, enabling you to rake up the applies into piles, quickly and easily
Then you just rake!
The rake glides, the loose apples bumble themselves towards you, and you can corral the apples into a couple of piles.
And when the roller apples fall apart, no problem - just stab a couple of new ones!
Having made a few biggish piles, I turn my tub-trug on its side, between my ankles, and scoop the apples into it, tipping them out into the wheelbarrow: then when the barrow is full, off to the compost pen they go.
Now here's a grand moment - my first ever gardening video! (If you don't count the occasional wildlife one...) I have no idea if this will work, but if it does, here is the Apple Roller in action, and do please bear in mind that I'm doing it one-handed while holding the camera in the other!
So, what do you with the apples that you rake up? Answer, pop them onto the compost heap. You can't have too many apples on a compost heap! Even if they are mouldy, squishy, rock hard, it does not matter - tip them in, and no matter how many you put in:
... they seem to rot down to nothing in a couple of weeks.
I suppose that apples are mostly water, after all.,
And yes, this applies to crab apples, eaters, cookers, pears and plums as well.
And as a final note, if you want to make life easier for yourself, keep the grass cut short under your apple trees.