Keywords: Spot blotch, tan spot, Bipolaris sorokiniana, Pyrenophora tritici-repentis

Helminthosporium leaf blight caused by Bipolaris sorokiniana and Pyrenophora tritici-repentis is a very serious disease in non-traditional wheat growing areas of the world. Due to high influence of environment and high pathogen variability, its management is difficult. This study was conducted at IAAS, Rampur to study the effect of seeding dates on various susceptible and resistant cultivars of wheat for the management of the disease by manipulating the seeding date during wheat growing season of 2002. Six genotypes (RR 21, BL 1473, NL 297, Milanshanghai-7, NL 750, and NL 781) having different level of resistance and maturity were planted on Nov. 26, Dec. 11, and Dec. 26 on four replicated strip split plot design. Epoxiconazole 'Opus' was sprayed on vertical strip @ 0.05% Amount of fertilizer, seed rate, spacing and other agronomical practices were applied as recommended. Percent diseased leaf area (DLA) was scored from flag (F) and penultimate (F-1) leaves and plot disease was also recorded by using double digit scale (00-99) method and area under disease progress curve (AUDPC) was calculated. Results showed that seeding date had significant effect on AUDPC, AUDPC/d, flag leaf duration, days to maturity, plant height, grain yield, biomass yield, harvest index, and thousand kernel weight. AUDPC/d increased as delayed seeding and it negatively correlated with the yield and yield components. Grain yield and thousand kernel weight in non-sprayed plots decreased as delayed seeding. Flag leaf duration and days to maturity reduced as delayed seeding, and reduced the grain-filling period. RR 21 showed the highest AUDPC and yield loss. Early variety BL 1473 showed tolerant reaction as characterized by higher AUDPC and less yield loss. Late as well as resistant genotypes Milan/Shanghai-7 and NL 750 had also yield some. Spraying seemed much effective to prevent reduction in yield. Timely showing during Nov 26 is effective for controlling HLB and saving crop from severe yield losses.