Development of spray schedule for the integrated management of Alternaria leaf blight of safflower under field condition

Introduction

Safflower an ancient and highly adaptable crop has been cultivated for over 4,000 years, originally valued for its vivid red and yellow florets. Historically, it played a significant role in textile dyeing, as evidenced by references in ancient Egyptian and Mesopotamian records. Today, the significance of safflower has evolved beyond the dye production to include diverse applications in agriculture, industry and health. Safflower oil derived from its seeds is rich in polyunsaturated fatty acids particularly linoleic (75%) and oleic acids which are potent antioxidants (Furuya, 1987) [4] , making it a popular choice in culinary, cosmetic and industrial products. The oil's nutritional profile has also drawn attention for its potential health benefits such as reducing cardiovascular risks and managing cholesterol levels (Dajue and Mundel, 1996) [3] . Safflower is cultivated in over 60 countries worldwide ranging between latitudes 50°N and 23°S (Gilbert et al., 2008) [7] . Mexico is the largest producer, followed by India. In India, the primary safflower producing states are Maharashtra and Karnataka, which together account for (86%) of the country's total production with Maharashtra contributing (55%) and Karnataka 31 percent. Globally, safflower is cultivated on 6.94 lakh hectares, producing 6.27 lakh tonnes annually, with an average yield of 903 kg per hectare (Anon., 2020) [1] . In India, safflower is grown on 0.79 lakh hectares, yielding 0.61 lakh tonnes annually, with an average yield of 777 kg per hectare. The crop is predominantly cultivated in the Indian states of Maharashtra, Karnataka, Andhra Pradesh, Telangana, and Madhya Pradesh. Karnataka alone accounts for 0.41 lakh hectares, producing 0.33 lakh tonnes, with an average yield of 810 kg per hectare. In Karnataka, safflower is primarily grown in the districts of Vijayapura, Kalaburagi, Bagalkot, Belagavi, Yadgiri, Raichur, Gadag and Dharwad (Anon., 2022) [2] . Safflower is known for its tolerance to cold and drought (Majidi et al., 2011) [11] and its ability to extract soil water that is inaccessible to most other dryland crops (Weiss, 2000) [18] . Despite its significant potential and adaptability to a wide range of agro-ecological conditions, safflower remains underutilized by farmers. This is due to several challenges, including its extended rosette stage, spiny nature, relatively low seed oil content (30-38%), late maturity and susceptibility to various diseases and pests (Sujatha et al., 2008) [16] .

The major biotic stresses affecting safflower production include leaf spot diseases caused by Alternaria carthami Chowdhury, Cercospora carthami Sundararaman and Ramakrishnan and Ramularia carthami Zaprometov; wilts caused by Fusarium oxysporum Schlecht. f. sp. carthami and Verticillium alboatrum, Powdery mildew by Erysiphe cichoracearum f. sp. Carthami Milovtzova, Phytophthora root rot and insect pests such as aphids and the safflower fly (Kalpana Sastry and Chattopadhyay, 2005; Singh and Prasad, 2005) [9,15] . Among the various diseases affecting safflower, Alternaria leaf blight and Fusarium wilt are considered the most significant biotic constraints on production. Alternaria leaf blight caused by Alternaria carthami leads to annual yield losses of 25-60 percent (Singh and Prasad, 2005, Indi et al., 1988) with substantial economic consequences for farmers in the Deccan Plateau of India (Rao et al., 2014) [14] . The continuous practice of monocropping and the cultivation of susceptible conventional varieties are key factors contributing to the high incidence of these diseases with reduction in the seed size, seed volume as well as percent oil content (Kalpana Sastry et al., 1993) [10] . Hence, an attempt was made to study the relative efficacy and economics of use of different newer fungicides, botanicals and bio agents for the management of Alternaria leaf blight of safflower under field conditions to minimize the losses caused by the disease.

Materials and Methods

A field experiment was conducted during rabi season during 2023-24 to study the efficacy of different fungicides, commercially available botanical and biocontrol agents in an integrated approach for the control of Alternaria leaf spot of safflower and also to study the economics of use of different fungicides for the disease control. The experiment was sown during 1 st fortnight of September employing variety Annigeri-1 (A1) during all the year to have maximum infection and build-up of the disease and thereby rigorous screening of the fungicides, botanical and biocontrol agents against the disease. The crop was sown at 45 x 20 cm spacing with gross plot size of 2.7 x 5.0 m and net plot size of 1.8 x 4.6 m and 50:25 kg N and P2O5 were applied at the time of sowing as basal dose. There were 11 treatments as per the details given in Table 1. The first spray of the fungicides was applied immediately after the disease appearance at 500 lit ha -1 and further need-based 2 sprays were given at 15 days interval thereafter. The disease intensity was recorded on ten randomly selected plants at 7 days after the last spray. The seed yield was recorded after harvest. The data were subjected to statistical analysis by employing standard methods of analysis of variance (Panse and Sukhatme, 1985).

Results & Discussion

Among the spray schedules evaluated, the treatment involving the first application of Mancozeb 75% WP (0.1%), followed by a second spray of (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG (0.1%) at a 15 days interval, resulted in the lowest PDI values of 20.71 and 23.16 respectively (T 9 ) and with an mean PDI of 21.26 percent which found significantly superior over all the treatments. The next most effective treatment was two sprays of Hexaconazole 5% EC (@ 0.1%) (T 10 ), which recorded PDI values of 23.26 and 27.39 after first and second sprays respectively, with a mean PDI of (23.69). The first spray of (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG followed by a second spray of T. harzianum (10 g/l) resulted in a mean disease severity of 25.07 percent (T 8 ), which was on par with the two sprays of (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG (@ 0.1%) (T 6 ) with mean severity of 26.74 percent followed by two sprays of Mancozeb 75% WP (@ 0.1%) with severity of 28.47 percent. Two sprays of Azadirachtin 0.15% (@ 0.5%) (T 3 ) resulted in the highest disease severity, with severity of (38.00%) after the first spray and (49.44%) after the second, leading to a mean severity of (36.16%). This was next only to the control, which recorded significantly highest mean severity of (45.36%) (Table 1). The first spray of Mancozeb 75% WP (0.1%) followed by second spray of (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG (0.1%), resulted in the highest disease reduction over control (64.82%), which was significantly superior to other treatments (Table 1). This was followed by the treatment with (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG and T. harzianum (10 g/l), which achieved 58.40 percent disease reduction. The lowest disease reduction of (24.92%), was observed in the treatment with two sprays of Azadirachtin 0.15% at 0.5 percent (T 3 ). Wagh et al. (2017) [17] studied fungicides, biocontrol agents and botanicals under field conditions during 2013 and 2014 in safflower and found Hexaconazole at 0.1 percent recorded lowest PDI of 14.34 percent with seed yield increase of 54.56 percent and 3.22 B:C ratio. Hexaconazole acts by inhibiting fungal growth and reproduction by disrupting ergo-sterol biosynthesis, a key component of fungal cell wall.

Effect of different spray schedules on yield of safflower

There was considerable variation in yield across the treatments. Spray of Mancozeb 75% WP (0.1%) followed by (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG (0.1%) (T 9 ) resulted in the highest yield of 11.10 q/ha, outperforming other treatments. This was followed by two sprays of Hexaconazole 5% EC (@ 0.1%) (T 10 ) with a yield of 9.90 q/ha, and (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG followed by a second spray of Trichoderma harzianum (10 g/l), which produced a yield of 9.38 q/ha. The control treatment (T 11 ) had the lowest yield at 6.81 q/ha, followed by two sprays of Azadirachtin (0.15%) at (0.5%) (T 2 ) with a yield of 7.03 q/ha and two sprays Trichoderma harzianum @ 10 g/l (T 3 ) producing a yield of 7.22 q/ha. Results obtained in respect of efficacy of chemical and bioagent in effectively inhibiting these pathogens are in conformity with those reported earlier by Nzojiyobiri et al. (2003) [12] , Gaurilčikienė et al. (2008) [6] and Gaurilčikienė et al. (2012) [5] .

Economic analysis of integrated spray schedules on Alternaria leaf blight of safflower

The economic analysis and cost-benefit ratio for different treatments are presented in the (Table 2). The highest net income of Rs 17931/ha was achieved with the treatment Mancozeb 75% WP (0.1%) followed by (Tebuconazole 50% + Trifloxystrobin 25%) 75% WG (0.1%), which had a significantly superior cost-benefit ratio of 1.52 compared to other treatments. The next best treatment was, two sprays of Hexaconazole 5% EC at (0.1%) (T 10 ), recorded a costbenefit ratio of 1.46. The lowest cost-benefit ratio of less than 1 (0.93) was found in the treatment with two sprays of Azadirachtin 0.15% at (0.5%). Wagh et al. (2017) [17] studied fungicides, biocontrol agents and botanicals under field conditions during 2013 and 2014 in safflower and found Hexaconazole at 0.1 percent recorded lowest PDI of 14.34 percent with seed yield increase of 54.56 percent and 3.22 B:C ratio. Hexaconazole acts by inhibiting fungal growth and reproduction by disrupting ergo-sterol biosynthesis, a key component of fungal cell wall.

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