Scab of apple caused by Venturia inaequalis (Cke.) Wint has been the most dreaded disease on all commercial cultivars of apple in Kashmir valley. It has been receiving a worldwide attention on account of involving high expenses to restrict economic losses. In addition, it involves hazardous co-friendly concern and failure of a fungitoxicants and chance of development of resistant pathogenic strains. In the present study, series of experiments were conducted to explore the possibility of reducing the fungitoxicants spraying and devise appropriate strategies for the management of apple scab on cv. ‘Red Delicious’ within acceptable limits. Adoption of orchards sanitation practices in the preceding autumn/winter delayed the initial scab appearance by 9 to 22 days and checked the subsequent disease development as compared to unsanitated orchards conditions. The spray programmes in sanitated and unsanitated orchards were started at different phonological stages of apple after missing one to three initial sprays. All the identical spray schedules were more effective in sanitatied than in unsanitated orchards. The integration of fungitoxicants spray programmes and orchards sanitation resulted in a save of at least one initial spray and allowed to delay-start the spray programme effectively around pink bud stage or even later stage. Under Kashmir conditions, such a delay could lead to protect the eco-system from getting polluted with atleast 16.66% of fungitoxicants. The spray schedules used in sanitated orchards gave incremental benefit: cost ratio (IBCR) over unsanitated check ranging from 1:8.59 to 1:15.02 compared to 1:14.07 obtained in unsanitated orchards during 1996 and 1998. The disease intensity on fruits varied from 1.25 to 5.67% and 5. 83 to 23.58% in similar schedules of sanitated and unsanitated orchards, respectively. Sanitation practices alone provided highest !BCR of 1:22.31 with unsatisfactory disease control. Among most effective spray programmes, maximum IBCR of 1:11.27 was achieved in pink bud initiated spray programme and comprised of only five sprays. The spread of disease to varying distances of sanitated apple plantations from the sources of primary inoculum was also studied. The symptoms did not appear prior to petal fall in plantations about 120 meters away from the primary source as compared to their appearance at pink bud stage in zero or 60 meter distant plantations. The disease incidence in sanitated nursery plantation was directly proportion to the distance from source of primary inoculum. Autumn application of urea (5%) at pre-or post-leaf fall or both stages reduced ascospore production during green tip and petal fall stages in the following spring by 77 to 81% as against no urea. All the urea application timings reduced leaf litter density by 35.1 to 38.6% during leaf fall to bud swell and 17.4 to 19.4% during bud swell to pink bud and 40.0 to 48.3% during pink bud to petal fall stages compared to 31.6,20.5 and 35.2% reduced in check, respectively. Furthermore, no influence on commencement of green tip stages, floral/vegetative bud ratio and scab susceptibility of apple was observed in response to any of the urea application. Captan, carbendazium, hexaconazole and mancozeb applied at bloom stage of apple had non-significant influence on fruit-set and all were at least as good as recommended spray schedule in controlling scab. Spray schedule based on scab forewarning provided by ‘METOS’ device was for the first time evaluated in Kashmir valley and saved one to three sprays compared to protective spray schedules. The ‘METOS’-based-, 10-14 days interval and recommended-spray schedules provided better leaf and fruit scab control even upto pre-harvest than schedules of single application technique. These investigations have established the importance of orchard sanitation and use of disease forewarning ‘METOS’ device for better management of apple scab reduced fungitoxicants sprayings.
PhD Thesis submitted to SKUAST Kashmir