I planted an asian pear this winter, the leaves emerged and it was doing well for about 4 weeks. Then I noticed that the leaves were curling. A few have even fallen off! I have found some aphids but not enough to make all of the leaves curl;certainly not fall off. There is some evidence of chewing but only on a few leaves. I sprayed with pyrithrum a week ago and I thought it might help but it seems not. Three more leaves fell off today. What's going on? Any ideas?

I know this reply is a long time coming, but if you had this problem last year you will probably have it again.
Aphids will cause leaves to curl and pucker, visually somewhat like peach leaf curl. They have a hollow needle-like piercing mouth part that is used to extract sap (with sugar) from the leaf. They will not chew any holes or notches in leaves.
Aphids like young tender leaves, therefore, remove the sucker growth as soon as you see it.

Control with a soap spray. Soap is a contact poison so the spray must hit the pest. (Good for all soft bodied insects, including red sugar ants)
Make your own soap spray with Fels Naphtha bar soap.
• shave 1 inch Fels Maphtha into 1 quart water - dissolve (may have to heat) - this is yor soap concentrate
• add 1 tablespoon soap concentrate to 1 quart water - this is your spray
* for added "killing power" add 1/4 cup rubbing alcohol
SPRAY AWAY
Ted

The 1/4 cup of alchohol is added to the quart of concentrate, or the spray?

Do you suppose this would kill the dreaded Pear Blister Mite?

Alcohol added to the spray. Don't know about the blister mite.
Ted