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Influence of Potassium on Helminthosporium Cynodontis and Dry Matter Yields of ‘Coastal’ Bermudagrass¹

A study was conducted to investigate K nutrition in relation to occurrence of a leaf spot disease identified as Helminthosporium cynodontis Marig. on ‘Coastal ’ bermudagrass (Cynodon dactylon L. Pers.) grown on sandy soils of east Texas. Previously studied research plots of Coastal bermudagrass production via clipping removal were used. These were located on Darco (Grossaronic Paleudult; loamy, siliceous, thermic) and Cuthbert (Typic Hapludult; clayey, mixed, thermic) soils, typical of those used in forage production in east Texas. The influence of applied K at 112 and 224 kg K/ha with varying P on incidence of the disease, tissue K levels and exchangeable soil K was measured. Disease severity was curvilinearly related to tissue K levels. Midseason tissue K levels of 0.60% or less were associated with progressively increasing disease severity and decreasing dry matter yield. The first increment of 112 kg K/ha decreased disease severity and increased dry matter yield substantially. Phosphorus supply without K appeared to slightly aggravate the disease, possibly due to nutrient imbalance. Longevity of intensified forage production without K fertilization before development of the disease anomaly was soil dependent and varied from two production seasons for the Cuthbert soil to six seasons on the Darco soil. Differences in soil K reserves and soil depth were apparently responsible for the timing of the K related problem.

Key Words: Phosphorus • Disease • Forage production • Exchangeable K • Tissue analysis • Cynodon dactylon

² Respectively, formerly associate professor, the Texas A & M Univ. Agric. Res. Ext. Ctr., Overton. Presently, professor, Texas A & M Univ. Agric. Res. Ext. Ctr., Box 10607, Corpus Christi, TX 78410; and formerly Texas A & M Ext. plant pathologist, Overton, presently located Hidalgo County, Edinburg, TX 78539.

Received for publication July 12, 1978.

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