الفهرس 
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Abstract
Potato late blight caused by Phytophthora infestans (Mont.) DeBary, is an important destructive disease causes a considerable loss of potatoes crop all-over the world.
The potato late blight forecasting service in other countries has proved very success since enabled the farmers to protect their potato crop against late blight by timely preventive spraying. The purpose of the present study is to find out the possibility of forecasting late blight of potato for the main potato production regions in Egypt. So, that adequate blight preventive spraying could be applied by farmers.
The disease was detected during winter seasons in 1998/1999 to 2000/2001 in potato growing regions. Disease severity was low as 5-20% in Badrashin, Kafr El-zayat and Bosaily provinces during winter season 1998/1999, and very high 80-95% in Badrashin, Kom Hamada, Badr, Meet Ghamr and Salhia provinces during winter seasons 1999/2000-2000/2001. Also, the disease was less than 20% in Kafr El-zayat and Bosaily during winter seasons 1999/2000-2000/2001. There were positive relationships between late blight disease severity and environmental conditions during winter periods.
Three systems were selected and tested for describing the occurrence of late blight epidemic by combining weather conditions factors (disease severity value). These systems were of Beaumont 1947, Cook 1949 and Hyre 1954. As results of this study, new system was created by modifying Hyre system to be appropriate the Egyptian conditions.