Alternative Safety Methods for Controlling Powdery Mildew in Squash under Field Conditions

Almond (Prunus dulcis), camphor (Cinnamomum camphora) and clove (Syzgium aromaticum) crude oils, silicate, Gram-positive bacterium Streptomyces griseus and a fungus Gliocladium virens culture filtrates in addition to Topas-100 EC (10% penconazole) were used to study of their effects on powdery mildew caused by the fungus Erysiphe cichoracearum. Camphor oil (5 ml/L), clove + camphor + almond (2 and 5 ml/L), G. virens filtrate and Topas-100 (240 ppm) completely inhibited the conidial germination after 24, 48 and 72 h. Topas-100 treatment was the most effective treatment in reducing powdery mildew disease severity of squash with an average of 10.34%, followed by clove oil (5 and 10 ml/L), camphor oil (5 and 10 ml/L) and the mixture of clove + camphor + almond (5 and 10 ml/L) with averages of (13.70 and 11.43%), (16.31 and 15.84%) and (20.65 and 18.34%), respectively. Concerning the disease incidence, it showed a harmony trend with the disease severity. Squash shoot length, leaf area/plant and the number of leaves/plant increased due to the treatments compared to the control treatment (infected only). The filtrates of S. griseus and G. virens had moderate effectiveness on the previous parameters. Also, it is clear that the plant fresh and dry weights, number of fruits/plant and weight of fruits/plant increased significantly compared with control treatment of squash plants. The treatments of Topas-100, clove + camphor + almond (10 ml/L and 5 ml/L), G. virens and S. griseus filtrates had the highest chlorophyll a content with averages of 4.02, 3.95, 3.79, 3.58 and 3.47 mg/g fresh weight, respectively. Also the same arrangement cleared in case of chlorophyll b with averages of 3.34, 3.00, 2.98, 2.83 and 2.75 mg/g, respectively. All treatments used increased the activity of defence-related enzymes (polyphenol oxidase and peroxidase). The activities of pectin methyl esterase, Cx-cellulase and polygalacturonase enzymes were in parallel with the disease severity where the activity of any enzyme from them increased with the increasing of disease severity.