Learn Croatian: Nemojte jesti te prljave maline. - Don't eat those dirty raspberries.

Both mean "do not eat", but using nemojte followed by the infinitive (jesti) is the most common and standard way to form a negative command. Using ne plus the imperative (ne jedite) is also correct but can sound a bit more direct or abrupt.

What case is te prljave maline in, and why?

It is in the accusative case because it is the direct object of the verb jesti (to eat). For feminine plural words, the accusative endings are identical to the nominative endings, which is why te prljave maline looks exactly like the subject form.

Jesti is an imperfective verb. Could we use the perfective pojesti here instead?

In negative commands, Croatian strongly prefers imperfective verbs. Nemojte jesti is the natural way to say "don't eat." Using the perfective (nemojte pojesti) would sound unusual here unless you specifically meant "don't finish off" or "don't eat all of" those raspberries.

Why use te instead of one for "those"?

The word te points to things that are physically or conceptually near the person you are talking to. If the raspberries were far away from both of you, you would use one.