One apple per cluster.

And thin out some of the clusters, too.

I usually follow the same method Itilton suggested. By now, the baby fruit that wil not make it usually show sign of stems yellowing and will fall off.

I admit, once in a while, I let the two biggest fruitlets in the cluster grow, granting I make sure the branch can support them. I've never let 3 in a cluster grow. My apple tree (William's Pride) is still young.

Leaving one apple per cluster would be way too many for my trees. I think that's a really poor way to decide how many apples to leave. After all how many clusters do you have and how far apart? But then I prefer return bloom and really high quality fruit.

Don't leave so much that it runts out your tree. That's probably the worst that can happen.

Usually the reality of bagging causes me to thin a little more. And I've had some bad stone fruit already this year partly due to leaving too much fruit. So I'm on a thinning kick.

Thanks all. Since I've had most of my trees for only 5-6 years, I still consider them very young. I'll thin according to your instructions. Thanks all. Mrs. G Egad! don't want runting trees!

The other downside to not thinning enough is that the trees may decide to thin for you in June. It's not good to see a bunch of painstakingly hung bags on the ground.

On some of my smaller trees, I actually thinned the flowers out, hoping to save energy for the trees. It also makes for less work later (and there were fewer leaves to get in the way).

I started this year's bagging last week (30-40) and used up a complete box (125 count) of bags today. There is more to go, but I am most of the way done. Last week I saw almost no hits, but now, I'm seeing quite a few PC bites, which I am thinning off. I've been careful to collect them all for the trash, rather than letting them sit on the ground where they could hatch.

Interestingly the hits seem to be non-uniformly distributed. Egremont and Roxbury Russets both had almost complete coverage...to the point where I was considering bagging a few ER with bites (hoping the apple would grow fast enough to crush the eggs), just to have something. While the Kidds Orange Red (right in between the 2 above trees in the row) was almost free of bites. Next year, I think I'll need to bag those 2 first.

PC damage has been really heavy this year, very early.

I think one reason is that it's actually pretty late, in calendar terms, not fruit maturity terms. I think the PCs are going by the calendar and getting impatient while no fruit was set for so long.

As Itilton stated "And thin out some of the clusters, too. "
I thinned out a number of clusters esp. ones next to the ones I keep or in bad spots.

Like Fruitnut, I tend to thin more since I have had good experience with good quality fruit (large and fully developed) after aggressive thinning. I prefer quality over quantity for my fruit.