 These chemicals may limit the growth of established plants or the germination and growth of seeds and seedlings.Another of the ways in which the ecological role of a plant can make it a weed even if it is in itself inoffensive, is if it harbours a pest that is dependent on it for survival; for example, "Berberis" species are intermediate hosts for stem rust fungi, so that they promote serious damage to wheat crops when growing near the fields.A number of native or non-native plants are unwanted in a specific location for a number of reasons.