Susan from NZ sent the Phactor a question. Her plum tree has some large, whitish fruits instead of the green, olive-like normal immature fruits. She wondered if perhaps they were pollinated by some other exotic fruit tree, but no. This is the result of a fungus disease, Taphrina pruni, infecting the fruit and altering their development. This is not as common as another species of this fungus that causes peach leaf curl. The first time you see this disease it can be quite strange because of the appearance of the fruits. Here's an image from Susan that shows both normal and infected young plums. But as you may guess, a heavy infection destroys your crop.