Take-all Patch Suppression in Creeping Bentgrass with Manganese and Copper

Take-all patch, caused by Gaeumannomyces graminis (Sacc.) Arx. & D. Olivier var. avenae (E.M. Turner) Dennis (Gga), is a disease of creeping bentgrass (Agrostis stolonifera Huds.), which most often is associated with golf courses. Synthesis of ligneous and phenolic compounds by plants requires adequate Mn and Cu nutrition and may be a factor in disease resistance. An experiment was conducted on a creeping bentgrass fairway naturally infested with Gga to determine if foliar applications of Mn (1.02 and 2.04 kg·ha per application) and Cu (0.68 kg·ha per application) would reduce take-all severity. Prior to initiating treatments, soil pH was 6.4 and Mehlich-3 extractable Mn and Cu were 5 mg·kg and 1.7 mg·kg, respectively. Manganese and copper sulfate treatments were initiated in July 1995 and foliarly applied every 4 weeks through 1997 with the exception of December, January, and February. Disease incidence was decreased from 20% on untreated turf to 5% with the high rate of MnSO4. For both years, turf treated with the high rate of Mn had less disease than turf receiving the low rate of Mn. The application of CuSO4, however, did not influence disease development. Take-all patch is caused by Gaeumannomyces graminis (Sacc.) Arx. & D. Olivier var. avenae (E.M. Turner) Dennis (Gga), and is primarily a disease of Agrostis spp. A related organism, Gaeumannomyces graminis (Sacc.) Arx. & D. Olivier var. tritici (Ggt), is a serious root disease of wheat (Triticum aestivum L. em. Thell). Garrett (1981) reported that the disease could be effectively suppressed by mineral nutrition and soil management practices that lower soil pH. The optimum pH for the growth of Ggt is 7.0 (Marschner, 1995). The severity of wheat takeall is influenced by Mn availability in the rhizosphere and the Mn concentration in roots (Huber and Wilhelm, 1988). Soil application of Mn fertilizers helps to suppress wheat take-all on non-calcareous soils. In high mowing height and clippings were removed. Applications of a 16N–2P–7K fertilizer, which contained ammonium phosphate, ammonium sulfate, potassium chloride, iron sulfate, and iron oxide as nutrient sources, were made monthly for a yearly total of 146 kg·ha N. The Mn and Cu fertilizer treatments listed in Table 1 were initially applied on 27 July 1995, and with the exception of December, January, and February were applied every 4 weeks throughout 1996 and 1997. Commercial sources of manganese and copper, dissolved in 1 L of water and sprayed over 4.3-m × 6.1-m plots with a backpack sprayer calibrated to deliver 374 L·ha. The turf was irrigated with ≈1/3 cm of water after treatments were applied on hot sunny days to reduce the potential for foliar injury. Initial treatment rates (1.53 and 3.05 kg·ha Mn per application; 1.02 kg·ha Cu per application) were reduced by one-third as shown in Table 1 after the first application on 27 July 1995. This was due to concern by the golf course superintendent about the potential for foliar injury. The experimental design was a randomized complete block with six replications. Composite soil samples of five cores (0 to 5 cm) and the thatch were collected from each plot just prior to the application of treatments on 27 Mar. 1996 and 11 June 1997. Soil samples were analyzed for Mehlich-3 (Mehlich, 1984) extractable Mn and Cu. Soil pH was determined using a 1 soil : 1 water (by volume) ratio. The Mn availability index (MnAI) was used to determine the soil Mn status (Mascagni and Cox, 1985). The MnAI is a function of both soil pH and Mn extracted by the Mehlich-3 extractant: M3MnAI = 101.7 – 15.2 (pH) + M3Mn (no units). The incidence of take-all patch was recorded on 30 May 1996 and 20 June 1997 to determine the effects of the treatments on symptom expression. Disease incidence was calculated from a grid that was placed over each plot. Cross marks falling on necrotic tissue were counted as disease. Incidence is reported as the percentage of the plot area that was affected by the take-all fungus. Statistical analyses of the disease data were performed using the GLM procedure of SAS. Single degree of freedom contrasts also were evaluated to test treatment effects. Results and Discussion Take-all patch was observed each spring and disease ratings were taken on 30 May 1996 and 20 June 1997. There was no phytotoxicity observed for any of the treatments. The application of Mn reduced disease severity in both years (Table 2). Plots treated with the high rate of Mn exhibited less disease than turf receiving the low rate of Mn. In both years, disease incidence was decreased from 20% on untreated turf to 5% with the high rate of Mn. Treatment effects were apparent for the period of time that disease symptoms were expressed (late spring to mid summer). These findings suggest that Mn may play a role in improving the resistance of creeping bentgrass against take-all. pH soils, Mn is rapidly oxidized and made unavailable for plant uptake. Supplying N fertilizers in the ammonium form helps to lower soil pH and increase Mn availability (Thompson et al., 1995). Soil application of Cu also helps to reduce take-all of wheat grown on soil deficient in copper (Gardner and Flynn, 1988). Applications of manganese and copper are thought to increase the plant’s resistance to disease through utilization of these elements in the increased synthesis of phenolic and ligneous compounds. These compounds may serve as chemical barriers in plants to increase take-all resistance of wheat, even in soils adequately supplied with Mn and Cu (Graham and Rovira, 1984). The objective of this study was to determine the effect of Mn and Cu fertilization on the control of take-all patch of creeping bentgrass. More emphasis (two rates) was placed on manganese applications since there was more evidence in the literature to suggest that Mn would have an effect on take-all. Materials and Methods An experiment was conducted on the third fairway of the Metedeconk National Golf Course in Jackson, N.J., where the creeping bentgrass turf (‘Penncross’ and ‘Penneagle’) was known to be infested with Gga. The fairway was established on a modified Lakehurst sand (mesic-coated Haplaquodic quartzipsamment) soil 10 years prior to the initiation of the experiment. The experimental area was maintained under normal fairway management throughout the duration of the study. The golf course crew used an 11-mm