Willow oak (quercus phellos) make good bonsai. Probably the best oak among the Eastern oaks for bonsai, as the leaves are in scale and reduce. It is shallow rooted, tough hardy and pretty easily collected. I would not dig this late in the year though.

Collecting this tree would be much like collecting any other. You sever the roots, dig it up and put it in a container with good bonsai soil that drains. Refrain from design work for two years.

You have to get the hang of collection before you go after the truly magnificent specimens out there. If you're still losing a signficant number of the trees you collect, perhaps you should wait on this one.

Zack,
Be patient. Take your shovel out this fall (leaf drop) and just cut the roots in a semi-circle (half way around) about the size of the rootball you want to finally collect. Do it again next fall, on the other half and then the following spring go and collect your tree. This is all presuming you are on good terms with the landowner. With this prep the feeder roots will all be within the rootball you want to collect.
Patience,
Vernon

After watching this tree for several years, I now don't have two years to collect it. Any idea on making the half cut now and then keeping it well watered with willow water and collecting it next spring? Zack

Is the tree in danger of being bulldozed or otherwise destroyed? If not, and you're killing collected trees, you'd better take the time. Impatience kills the majority of new collectors' trees.

Collecting it right now is a death sentence. Fall is marginal. Spring is best. All ths depends, or course, on landowner permission.

Rushing collection isn't a great thing to do, especially when you're working with a nice tree with alot of potential. There's nothing like watching all your plans circle the drain as the collected tree fades and dies weeks, months or even a year after you collect it. I've been there...

If it is in danger, dig it up--get as much rootball as you can. Eliminate the field soil with water sprayed from a garden hose--get the plant into a growing box with well draining bonsai soil, keep your fingers crossed.

This method is bare bones and will stress the tree greatly. You will have to monitor watering--making sure the soil stays moist, not wet. You will have to judge the amount of sunlight the plant gets post collection, too much will kill it, too little won't stimluate new budding. You will also have to decide how much top reduction has to be done to minimize impact on the roots, but leaving enough to pull the plant through. You will have to provide shelter for it in the winter--not indoors, but in a cold, but not frigid area, out of the wind.

Willow water will be of only minimal, if any help. It is not the cure all it's made out to be. It can help, but it's not going to pull the tree through this process. That task is yours and yours alone. Knowledgeable watering, soil composition, and placement in the correct growing conditions are far more important factors in collected tree's recovery than additives to water. If you're stil working to get this knowledge, I'd wait to collect the tree.

Good luck.