Abstract
In a simulated landscape planting in Brewton, AL, the impact of fungicide treatments on severity of Entomosporium leaf spot was assessed on 13 selections of Indian hawthorn, which range from highly susceptible to resistant to this disease. Chlorothalonil [Daconil 2787 4.17F] at 1.25 g ai/liter was applied at 2-and 4-week intervals to a randomly selected plant in each plot. The remaining plant in each plot was not sprayed and was the untreated control. From mid-winter to mid-spring in 1997, 1998, and 1999, fungicide applications were made over a 13-to 15-week period. When compared to unsprayed controls, reductions in the severity of Entomosporium leaf spot were noted on the fungicide-treated plants of nearly all selections, regardless of their susceptibility to Entomosporium leaf spot. As expected, disease severity was usually lower on those plants sprayed at 2-week rather than 4-week intervals. While chlorothalonil significantly reduced disease severity on the Entomosporium leaf spot resistant selections ‘Indian Princess’®, ‘Clara’, ‘Snow White’, ‘Olivia’™, and ‘Eleanor Tabor’™, only a limited reduction in the number of infected leaves in the canopy and perhaps a minor reduction in premature leaf loss were seen. In contrast, substantially less leaf spotting and defoliation on the selections such as ‘Spring Rapture’®, ‘White Enchantress’®, ‘Enchantress’®, ‘Heather’, ‘Harbinger of Spring’®, ‘Pinkie’, and ‘Bay Breeze’® were obtained with chlorothalonil, particularly when this fungicide was applied at 2-week intervals. When treated with chlorothalonil at 2-week intervals, disease severity on susceptible selections was, however, comparable to the damage levels observed on the unsprayed leaf spot resistant selections. When compared with costly and labor-intensive fungicide inputs, production and establishment of disease resistant selections is the preferred strategy for preventing destructive outbreaks of Entomosporium leaf spot on Indian hawthorn in the nursery and landscape.
Impact of Fungicide Inputs on the Severity of Entomosporium Leaf Spot on Selections of Dwarf Indian Hawthorn