How to remove noise from leaf image

Hi,

I'm asking this questions after spending a lot of days researching without getting an solution for my problem (the good thing is that I've learned a lot).

Well, I have a dataset of leaf images and I will compare their texture to check what's their level of a certain disease. Before working on the code to make comparisons, I've been working on leaf segmentation to remove background (or just make it totally black). I got a binary image and the code was working for some of them, but then I got a bunch of images that have something like a noise in the background and which I'm not able to remove.

I'm pretty new to Matlab, so I'm not sure if this kind of noise is a speckle, salt and pepper or anything else. I just see it when I transform the image to a binary one.

I've attached the original image and the binary image (where you can see the noise in a better way). Most of that it's on top, at left.

Does anyone know how to remove this type of noise from images? I've used medfilter and colfilt, but the results are not good.

Thank you in advance.