It leads to less efficient use of the land. Higher costs to control insects and plant disease organisms that attack crop pants. All types of crop products may be reduced in quality. The seeds and bulblets in grain, spindly leaf crops, and scrawny vegetables are a few examples. Livestock products may be lower priced or unmarketable because of weeds, for example, onion, garlic or bitterweed flavour in milk and cocklebur in wool reduce the quality of products.
Weeds are important in irrigation and drainage systems.
They may give off undesirable flavours and odours in public water supplies. They affect recreation and fishing on ocean beaches, lakes and farm dams. Some alien plants reduce human efficiency through allergies and poisoning. Alien plants pose a great threat to ecotourism in the KwaZulu Natal coastal belt. These plants are aggressive growers and a seedbank is created where seeds can lie dormant for up to 50 years.