Continuous Hours of Leaf Wetness as a Parameter for Scheduling Fungicide Applications to Control White Rust in Spinach. F. J. Dainello, Research Horticulturist, Texas Agricultural Experiment Station, Uvalde 78801. R. K. Jones, Plant Pathologist, Texas Agricultural Extension Service, College Station 77843. Plant Dis. 68:1069-1072. Accepted for publication 18 May 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-1069.

The timing of fungicide applications to control white rust of spinach based on continuous hours of leaf wetness (CHLW) was evaluated in three experiments. Chlorothalonil applications after 6, 12, and 18 CHLW were compared with an unsprayed check and a 10-day fixed schedule in both fall and spring plantings of the spinach cultivar Iron Duke. The 6- and 12-CHLW treatments were as effective as the fixed schedule in reducing white rust in both plantings. The potential for using 12, 18, and 24 CHLW to time metalaxyl sprays compared with a 7-day schedule under multiharvest conditions was investigated using the cultivar Chinook. Under these conditions, the 12-CHLW treatment also provided the same level of control as the fixed schedule but required five fewer applications. The rate of disease progression as influenced by metalaxyl applications based on 12, 18, and 24 CHLW was also studied. Although the incidence of white rust increased in unsprayed, 18-, and 24-CHLW plots, similar levels of disease control resulted from the 12-CHLW treatment and the fixed schedule.

Keyword(s): Albugo occidentalis, Peronospora effusa, Spinacea oleracea.