Orlah 2:1

Terumah, terumas maaser – even of demai, challah, and first fruits – are all nullified in a ratio of 1-in-100. These all combine with one another and one must remove the requisite amount and give it to a kohein. Orlah and mixed species grown in a vineyard are nullified in a ratio of 1-in-201, they combine with one another and one need not remove a portion. Rabbi Shimon says they do not combine; Rabbi Eliezer says they combine when they impart flavor but otherwise not.

Orlah 2:2

Terumah and orlah can nullify one another in the appropriate ratios. For example, if a seah of terumah falls into 99 seah of regular produce and then three kav (= half a seah) of orlah or mixed species from a vineyard fell in, then the terumah and the orlah cancel one another out.