Stored-grain insects can also produce great damage. Species in the genera [Ephestia], [Rhyzoperta], [Sitophilus], [Tribolium], [Sitotroga], [Cathartus], [Dinoderus] and [Trogoderma] have the widest distribution and cause major damage in stored grains. Maize rusts (especially [Puccinia sorghi] and [P polysora]) and leaf blights (especially [Helminthosporium turcicum] and [H maydis]) are the most damaging diseases. Rust due to [Puccinia sorghi] is found in the USA and is common throughout highlands of subtropical areas of Latin America and Africa. Previously regarded as of minor importance, [P sorghi] rust became increasingly prevalent in the USA during the 1950s when open pollinated varieties of maize were replaced by [P sorghi] susceptible hybrids. The rust caused by [P polysora] is of some importance in southern USA, but is more common in the tropical areas of the Americas. Since 1948, it has spread with remarkable speed. In 1949 it was found in Sierra Leone, and in 1950 in the Ivory Coast, Ghana and Southern Nigeria. Then it moved on to the Cameroons, to east Africa and far as Zululand. A few months later it was spreading through the scattered islands of the Indian Ocean, reaching Mauritius, Reunion, Madagascar and the Seychelles. Finally from these islands it invaded North Borneo, Thailand, Malaya, and the Philippines. The effect of the maize varieties grown in Africa and Asia was devastating, with up to 70% crop losses. Thus it was and still is a fearful threat to all those Africans and Asians dependent on maize for much of their food. [Helminthosporium turcicum] leaf blight is common in cool, moist areas, and may decrease yields mainly when infection occurs at the silking stage of the plant. [H maydis] race T caused great losses on maize production of USA during the early 1970s due to susceptible germplasm included in commercial hybrids through the incorporation of Texas male-sterile cytoplasm source. Probably this has been one of the most devastating maize diseases ever known.
Other economically important maize diseases are stalk rots and ear rots. Stalk rots cause wilting of the plants before or after pollination thus decreasing their yield. Several ear-rotting fungi are known to affect the yield and quality of grain produced. Several mycotoxins have been identified produced by fungi, mainly in the genus [Aspergillus] and [Fusarium] which affect birds and mammals fed with infected kernels. Of major concern are the downy mildews of maize caused by several species in the genera [Sclerospora], [Sclerophthora] and [Peronosclerospora]. These diseases were originally reported as limiting factors in maize production in Southeast asian countries, and later the disease spread to African countries where maize and sorghum are cultivated. Since 1964 the disease was reported in southern Texas and northeast Mexico and has expanded rapidly in humid tropics of the Americas, probably through contaminated seed. Diseases caused by viruses (such as Maize Streak transmitted by leafhoppers of the genus [Cicadulina] in countries of tropical subequatorial Africa, Rayado Fino transmitted by the leafhopper [Dalbulus maidis] in Latin America and southern USA, Maize Dwarf Mosaic Virus transmitted either through infectious sap or the aphid [Rhopalosiphum maidis]) are creating concern in maize growers around the world. Spiroplasma-caused diseases like Corn Stunt transmitted mainly by the leafhopper [D maidis] is important in tropical Latin America, the Caribbean and Southern USA.