Não informado. Leaflet. Purdue University, Agricultural Extension Service.
Chicago-referens (17:e uppl.)Não informado. Leaflet. Lafayette, Ind: Purdue University, Agricultural Extension Service.
MLA-referens (8:e uppl.)Não informado. Leaflet. Purdue University, Agricultural Extension Service.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.