The dynamics of powdery mildew development on pumpkins

Abstract

Goal. To determine the spread and development of powdery mildew on pumpkins in the Forest-Steppe of Ukraine.
 Methods of investigation. The experiments were carried out in 2016—2018 biennium in the Right-Bank Forest Steppe of Ukraine (Khmelnytsky region) on the following varieties: common pumpkins — Ukrainskyi bahatoplidnyi, hull-less — Shtyriiskyi. Assessment of severity and spread of powdery mildew was carried out by conventional methods. The records were taken by visual method at 51, 73 and 89 stages (BBCH scale). Ten plants per plot were selected and spread and severity of the disease in percentage were determined.
 Results of investigation. During the period of investigation, powdery mildew was observed on the pumpkins of both varieties annually. Its first sympthoms were noted at the 15—17 stage. According to the morphological and biometric features, the pathogen identified as Erysiphe cichoracearum (DC.) V.P. Heluta. In the varieties studied, powdery mildew was found with a non-significant difference in severity and spread. In 2016, the severity of powdery mildew on pumpkins of variety Ukrainskyi bahatoplidnyi varied in the range of 15.4—19.5%, disease spread — 45.1—49.6%, on variety Shtyriiskyi development was 13.3—17.5%, distribution — 46.2—48.1%. In 2017, we obtained the following results: the disease severity for common pumpkins was in the range 13.2—17.4%, disease spread — 42.8—46.7%, for hull-less pumpkins disease severity was 12.2—16.8%, disease spread — 41.7—45.3%. In 2018, severity of powdery mildew was higher than in previous years, accounting for 21.2—26.7% with spread 50.4—55.2% on common pumpkins, and 19.4—25.3% with spread 48.8—54.2% on hull-less pumpkins. The correlation analysis of the data showed that the closest correlation between the spread and the development of the disease was observed with the precipitation and GTC in June.
 Conclusions. Dynamics of severity of powdery mildew during 2016—2018 years on common and hull-less pumpkins were studied. At stage of full ripening, the maximum rates of spread and severity of the disease were noted, which averaged 49.2—50.5% and 19.9—21.2% over the three years, respectively. No significant difference in the powdery mildew infection between common pumpkins (variety Ukrainskyi bahatoplidnyi) and hull-less pumpkins (variety Shtyriiskyi) was found. The defining conditions for the development of powdery mildew on pumpkins are the weather conditions in June, most notably the presence of increased moisture during this period.