Relationships between potassium, chloride, and disease incidence in St. Augustinegrass and bermudagrass

Abstract

Potassium and chloride both suppressed Rhizoctonia blight in St. Augustinegrass and the two combined together as KCl was superior to K or Cl applied separately. Potassium applied as K₂SO₄ showed little disease suppression. Increasing rates of KCl on a Tifgreen bermudagrass green showed a strong correlation (r² = 0.9700) of reduction of dollar spot. K applied as K₂SO₄ and Cl applied as CaCl₂ had little effect. Glasshouse results showed increasing K applied as K₂SO₄ from 0 to 97.6 kg ha⁻¹ and Cl applied as CaCl₂ from 0 to 97.6 kg ha⁻¹ reduced dollar spot infection by 26% 1 week after inoculation. Bipolaris cynodontis infection on common bermudagrass in the field was reduced by 26% as Cl applied as CaCl₂ increased from 0 to 48.8 kg ha⁻¹ and K applied as K₂SO₄ increased from 0 to 48.8 kg ha⁻¹. Glasshouse studies showed increasing Cl applied as CaCl₂ reduced Bipolaris cynodontis on Tifgreen bermudagrass by 20% 1 week after inoculation and 30% 2 weeks after inoculation as rates of Cl increased from 0 to 97.6 kg ha⁻¹. Dollar spot infection of glasshouse-grown Tifgreen bermudagrass was reduced by 26% and 33% one and two weeks after infection as Cl applied a CaCl₂ increased from 0 to 97.6 kg ha⁻¹. Increasing K applied as K₂SO₄ reduced dollar spot by 26% and 21% one and two weeks after infection as rates of K increased from 24.4 to 97.6 kg ha⁻¹. Leaf tissue concentration of N was not affected by increasing rates of Cl applied as CaCl₂ or K applied as K₂SO₄ increased from 0 to 97.6 kg ha⁻¹. Leaf tissue K was not affected by Cl applied as CaCl₂ as rates went from 0 to 97.6 kg ha⁻¹ and increasing K above 48.8 kg ha⁻¹ did not increase leaf tissue K. Leaf tissue Cl decreased as K applied as K₂SO₄ increased from 24.4 to 97.6 kg ha⁻¹. Leaf tissue N from 20 to 24 g kg⁻¹, K from 13 to 16 g kg⁻¹, and Cl from 4.5 to 6 g kg⁻¹ had no effect on the infection by Bipolaris cynodontis on field-grown common bermudagrass.