Tuber infection occurs when spores are washed down to tubers. It cannot get into mature, intact tuber skin, but can enter through immature tubers, lenticles, eyes and wounds. Cross tuber infection is fairly difficult to accomplish, but can happen. Spores have a flagellum so they can swim down and infect a plant indirectly. Sexual reproduction is possible, but has not been documented yet in North America.
Late blight is more aggressive than early blight.
The new A2 strain may be more aggressive than the old A1 strain of late blight-some A1 types are very aggressive. This will result in late blight in your field, and seed infected with late blight usually doesn't emerge so stand problems will result. One of the first thing late blight does when it infects tubers is kill all the eyes. This has been shown to be an excellent way to spread late bight. This will also give you protection against late blight, you just need a lot for fungicides to control late blight. .