Grain sorghum grown in Arizona usually is not significantly damaged by diseases. Generally, fungicide applications are not economical for grain sorghum diseases. The most effective control measures are hybrid resistance and allowing at least 3 years between sorghum crops. Weed control can further limit disease introduction. Of the few diseases that have been described in Arizona, most have not been problematic in recent years. These include:
(1) Head smut, a fungal disease that infects the inflorescence and sometimes the foliage resulting in sooty vascular strands. In areas where disease occurs, only sorghum varieties with known tolerance should be planted.
(2) Maize dwarf mosaic virus (MDMV), an aphid transmitted virus that infects grain sorghum and Johnson grass. Johnsongrass is a common alternate host for the virus in Arizona.
(3) Fusarium root rot, also called Yuma root rot in Arizona, was reported in southwestern Arizona in 1972 in late planted sorghum. Several species of Fusarium cause root and stalk rots of sorghum and also are implicated in seedling and storage diseases, including mycotoxin production, but none has been a problem in Arizona to date. Tolerant varieties, earlier planting and good cultural practices have probably eliminated much of this problem.
(4) Root-knot nematode is probably the most common and easily missed pathogen on sorghum. Damage to sorghum is not always evident, but sorghum is an excellent host and causes problems when rotated with other susceptible crops such as corn, cotton, peppers and melons