Thanks for such a quick response! Should I be at all concerned about taking such a big chunk off of it with it having dropped a bunch of leaves recently?

It is clearly a rootstock sprout, it is below the graft line and note the long thorns on the sprout, a typical characteristic of vigorous juvenile rootstocks.

If it were me, I would cut it off now.

No, don't be concerned that you're cutting a big chunk off. Your Meyer is dropping leaves because it is putting all of its strength into that rootstock sucker. Cut that off ASAP and see if that helps with the lead drop, if not, it's possibly something else. What type of soil do you have your tree planted in? How often are you watering/ fertilizing? Have you potted it up since you recieved the tree? How much sun is it getting daily? This info will also help us with a diagnosis of what might be ailing your tree.

Evan

okay, thanks for the advice! I'll cut it off right away.

I'm guessing the leaf drop has something to do with the scale? I took it outside today and soaked it down with some organic insecticidal soap.

It's in front of a southern facing sliding glass door and gets about 5-8 hours of sun/day.

I potted it with miracle grow's citrus/palm soil when I first got it about three years ago.

I just ordered some citrus-tone, but I've been fertilizing every other week with a general fertilizer. And I water it every week.

Ok, the soil mix you have it in is very heavy, even though it is for palm and cactus it does not suit your Meyer trees needs. You can do a search here in the citrus forum for 5-1-1 mix or gritty mix and make your own soil that is much better suited to what your tree would need. Citrus tone is a good product for fertilizing, although not sure it is ideal for containerized trees. A lot of container folks on the forum use a product called dyna gro foliage pro and have great success. Also, Meyers are very sensitive to lighting condition changes so if you are just now re-introducing it to be outside for the spring and summer it will need to be done so over a 2 week period otherwise it will drop all of its leaves and grow new ones that are better suited for the change in light conditions. Hope this helps and I'm sure others will be along with much more info than I am able to provide.

Evan

next question, what's the best way to protect the tree where I may have poked through the bark while cutting that sprout off?

I would leave it alone, it will heal on its own.

ok, that's good to hear!