Influence of soil fertility on anthracnose and dollar spot of cool-season turfgrasses
Creators: name: Xu, Zhongqi
Publisher: name: No Publisher Supplied
Year: 2023

description: Anthracnose, caused by Colletotrichum cereale Manns sensu lato Crouch, Clarke, and Hillman, and dollar spot, incited by Clarireedia spp., are destructive diseases of cool-season putting green turf. Both diseases are influenced by soil fertility, but the effect of nutrients such as calcium (Ca) and potassium (K) on anthracnose and dollar spot, respectively, have not been extensively studied. Annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] is a common component of putting greens and is adapted to slightly acidic soil. Previous research has suggested that a mat layer pH below 5.5 and a low level of extractable Ca can increase the severity of anthracnose on ABG turf; however, additional research is needed to determine whether pH or Ca is the dominant factor affecting this disease. A 10-yr field trial was continued at the Rutgers Horticulture Farm 2 in North Brunswick, NJ during 2019, 2020, and 2021 with the objective of evaluating the effect of the soil amendments lime, gypsum, and sulfur on mat layer pH, mat layer and leaf tissue Ca, and anthracnose severity, and the anthracnose response to changes in mat pH, mat layer and leaf tissue Ca, and other nutrients on ABG maintained as putting green turf. Ten treatments were evaluated using a randomized complete block design with four blocks. Treatments consisted of five rates of lime, two rates of gypsum, two rates of sulfur, and one non-treated control. Lime increased and gypsum and sulfur had little effect on mat layer pH in all three years. Higher lime rates increased mat layer Ca quadratically on all observation dates and higher gypsum rate increased mat layer Ca linearly in May 2019, and September in all three years. Lime and gypsum increased leaf tissue Ca on most sampling dates. Sulfur did not affect mat or leaf tissue Ca. Higher lime rates decreased anthracnose severity on nearly all observation dates during 2019, 2020, and 2021. Although gypsum decreased anthracnose severity later in the growing season under higher disease pressure each year, the disease response was less consistent than lime. Sulfur rates, which were quite low to prevent foliar damage, had little effect on anthracnose severity compared to the non-treated check. Both the multiple regression and random forest models indicated that higher leaf tissue and mat layer Ca content decreased anthracnose severity measured as area under disease progress curve (AUDPC) over the three-year study. Higher mat layer pH only decreased AUDPC in 2021. Simple linear regression corroborated findings from the Shapley Additive Explanation and Random Forest Models that leaf tissue and mat layer Ca, year, and mat layer Mn were the major factors affecting anthracnose severity in this study. Mat layer pH appeared to have an indirect effect on anthracnose severity through its impact on nutrient uptake. Potassium is an essential nutrient for growth and stress tolerance of plants. However, the effect of K on the dollar spot of ABG and creeping bentgrass (Agrostis stolonifera; CBG) turf is largely unknown. Three field trials (ABG trial 1, ABG trial 2, and CBG trial 3) were initiated at the Rutgers Horticulture Farm 2 in North Brunswick, NJ in 2019 or 2020 to determine the effect of K fertilization on dollar spot severity of ABG and CBG turf mowed at 2.8-mm. A 4 × 2 factorial arranged as a randomized complete block design with four replications evaluated four levels of potassium [0, 3.4, 6.9, 13.8 kg K ha-1] applied every two weeks over 28 (ABG trial 1) or 20 (ABG trial 2 and CBG trial 3) weeks and two levels of N (urea) applied at 4.9 kg ha-1 every 7 days or 28 days over 28 (ABG trial 1) or 20 (ABG trial 2 and CBG trial 3) weeks. Each plot was inoculated with C. jacksonii in mid-September in 2019, 2020, and 2021. Infection centers were counted every 2 to 6 days over two weeks and used to calculate the area under disease progress curve (AUDPC) for each plot. Potassium fertilization had a more dominant effect on dollar spot severity than N, and greater K fertilization increased dollar spot severity on ABG and CBG grown under low mat layer K. Multiple linear regression analysis indicated that low K in the mat layer and leaf tissue were associated with lower dollar spot severity on both ABG and CBG. Relative to K, dollar spot responses to N were small and varied depending on the turfgrass species and year; nitrogen did not affect AUDPC in 2019 and 2021 and increased and slightly decreased disease severity in 2020 on ABG and CBG, respectively. The inconsistency of the N effect was likely due to the relatively low rates of N used in the current study.This research clearly shows that the Ca and K content of leaf tissue and the mat layer should be considered when attempting to control diseases like anthracnose and dollar spot on ABG and CBG turf. Further research is needed to determine the effect of a broader range of mat layer and leaf tissue Ca concentrations and other nutrients on anthracnose severity of ABG putting green turf. Moreover, additional research is needed to determine whether the observed dollar spot response to K is exclusive to turf grown under low K availability and occurs over a broader range of N fertilization rates and mowing heights. This will help improve best management practice recommendations for both dollar spot and anthracnose, particularly with respect to K which has the potential to reduced anthracnose severity of ABG and increase the severity of dollar spot on both ABG and CBG putting green turf.