In your dishwasher, it uses a lot of plastic parts purely because it is exposed to water as part of its regular function. However, when it comes to the dish racks on the interior, plastic just isn’t enough to cut it. Most dishwashers still use coated metal dish racks because they can withstand the weight of any dish and generally hold up well. However, over time, the protective layer of paint may wear down and you may notice rust starts to form.
Obviously, an easy solution is to just order a replacement dish rack. They aren’t terribly extensive and probably the easiest thing inside your dishwasher to install. However, with the right tools, it can also be repaired. All you need is a pair of wire cutting pliers and dishwasher rack coating that can be picked up at most appliance stores.
If the tines on your dish rack are the part that is rusting, you simply need to snip off the rusted part with your pliers. Afterward, you want to sand down the area and then apply the dishwasher rack coating liberally. You may want to use multiple coats if it is a high traffic area and the paint gets worn away so rust does not form again. You only have so much of the tine that can be snipped away so you only really get one or two repairs of it.
If an area of your dish rack is rusting where you can’t actually snip it away, what you can do is just sand and repaint it. However, it will require more sanding to make sure that you removed as much rust as possible before repainting. Just leaving the rust on the dish rack will still allow it to spread, so you want to get as much off as possible before covering it.