Potassium Influences Forage Bermudagrass Yield and Fungal Leaf Disease Severity in Mississippi

Fungal diseases in bermudagrass [Cynodon dactylon (L.) Pers.] and numerous other crops have been associated with K deficiency. This study evaluated how levels of K in potash fertilizer (0-0-60) and broiler litter influenced forage yields and severity of disease symptoms caused by a natural complex of fungal pathogens in ‘Tifton 44’ bermudagrass in Mississippi. The relative incidence at different K levels of six species of Bipolaris, Curvularia, and Exserohilum in the complex was also investigated. Disease symptoms were universal and strong in all plots in 2010, but weak and transient in 2011. Forage dry matter (DM) yields increased linearly and significantly (P < 0.05) as K-fertilizer rate increased from 0 to 167 kg K/ha. Disease severity in whole plots decreased as K levels increased in 2010, and severity of symptoms on individual leaves in 2011 was lower at 167 kg K/ha than 0 kg K/ha. The incidence of individual fungal pathogens on symptomatic leaves in 2010 ranged from 3 to 100% (E. rostratum and B. hawaiiensis were universal pathogens) and levels observed for four variable, non-universal pathogens did not differ between K-fertilizer rates. These results indicated that the reduced disease severity observed at the highest K levels was not caused by changes in the incidence of four fungal pathogens within the disease complex.