Abstract: Experiments were conducted to forecast the Potential Ascospore Dose (PAD) of the apple scab, caused by Venturia inaequalis (Cks.) Wint. (anamorph: Spilocaea pomi Fr.), was evaluated in Gangotri valley over 15 years (1994-2012) at four different place. In India, the disease causes significant economic losses in the states of Jammu and Kashmir and Himachal Pradesh each season and has been prevalent in Uttarakhand hills, the 3rd largest apple growing state in the country. Yield losses during epidemic years in 1996 and 2008 in the region went up to 70%. The PAD has great impact on disease development in the following season. It varied between 645-373421 in various orchards of Gangotri valley. The PAD value was low during 1999-2001 (645-1894 ascospore/m2) and medium during 2002-2006 (2108-29685 ascospore/m2) due to the fact that the springs were early, dry and unfavorable for ascospore maturation. In 1996 and 2008, the PAD values were high because of the favourable weather conditions and increase of inoculum accumulation. The scabbed lesion and leaf litter density were approximately more than twice in Gangotri fruit belt in 1996 and 2008. For this reason, reduction of primary inoculum sources played very important role in the improvement of scab management of apple in Uttarakhand Himalayas.