Effect of Temperature, Relative Humidity and Some Systemic Fungicides on Cucumber Downy Mildew and Certain Crop Parameters

Abstract

Downy mildew caused by Pseudoperonospora cubensis (Berk. and Curt) Rostow is a major disease of cucumber (Cucumis sativus L.) in Egypt. The current study was carried out in Fayoum, Ismailia and Kafr Elsheikh Governorates in summer and fall during of 2018 and 2019 seasons. The effect of some whither parameters on downy mildew was studied. Temperature, relative humidity, disease severity and their relationships were determined. Five fungicides Previcur N 72.2 SL, Veulet 80 WP, Previcur Energy 840 SL, Infinito 68.75 SC and Profiler 71.1 WG, were used for the disease control. Final disease severity (FDS), area under disease progressive curve (AUDPC) and fungicides efficacy were measured and analyzed. Scanning electron microscope was used for histopathological studies. Fresh, dry weight and the average number of fruits/plant and fruit yield/feddan (ton) were recorded. Kafr Elsheikh recorded the lowest average temperature, being 23.8°C during the two growing seasons followed by Ismailia and Fayoum, being 25.2°C and 26.9°C, respectively. Kafr Elsheikh, also recorded the highest average of relative humidity, being 53.3% during the two growing seasons followed by Fayoum and Ismailia, being 52.9% and 51.9%, respectively. The same trend was observed for disease severity that recorded the highest average in Kafr Elsheikh, Ismailia and Fayoum 36.2, 31.45 and 30.9%, respectively during the two growing seasons. On the other hand, the lowest average temperature and the highest average of relative humidity were recorded in