Solar radiation is high in Bulgaria during summer: in July and August, and quite often at the beginning of September. The total amount of radiation can reach 754.2 – 796.1 MJ/m2, and in Southern Bulgaria – even 838.8 MJ/m2. The maximum values of solar radiation are usually registered between 11 am and 4pm. For that reason the summer season is suitable for solarization (Lingova, 1995). The observations carried out during the months of July and August, in the period from 1993 to 1999, registered maximum air temperatures of 35-37оС, up to 39-41оС for the region of Plovdiv (EnviroCaster meteorological station, Neogen, USA). The reproduction structures of Phytophthora pathogens (sporangia, oospores, chlamidospores, and mycelia) can survive in the soil and solarization is a perspective/effective method for their control. Experiments carried out during 2008- 2009 registered temperatures above 30-35оС for long periods, and, what is more, it used to rise up to 35-39оС between 11 am and 4 pm. The eradication effect on Phytophthora structures is even enhanced, due to the accumulative effect of the temperatures in the 5–20 cm soil layer. For the 5 cm layer, the amount of hours with temperatures above 30оС was 253.43 Degree-hours (10.61 days), and above 35оС – 51 Degree-hours (2.1 days); for the 10 cm layer the amount of hours with temperatures above 30оС, was 401.26 Degree-hours (16.72 days) respectively and above 35оС – 125.58 Degree-hours (5.27 days); for the 20 cm, above 30оС – 416 Degree-hours (17.4 days) were accumulated and above 35оС – 15.9 Degree-hours (0.66 days).
Application of solarization for the control of phytophthora pathogens in rootstock production