Management of Alternaria Leaf Spot using Available Fungicides (Combi Products) in Sunflower

Sunflower is one of the major oilseed crop cultivated in India and in the year 2021-22, it occupied an area of 2.25 lakh ha with a production of 2.28 lakh tons and productivity of 1011 kg/ha (Directorate of Economics and Statistics, 2022) in India.Leaf spot/blight caused by Alternariaster helianthi (Hansf) Tubaki and Nishihara is one of the economically important diseases, responsible for yield losses of 20 to 80%, with oi1 losses of 20 to 30%, reported from tropical and subtropical sunflower production regions (Howard  and Gent, 2007).
       
In India, the disease was first reported by Narain and Saksena (1973), Kolte and Mukhopadhyay (1973) from Uttar Pradesh.The pathogen reduces seed germination and seedling survival (Udayashankar et al., 2011) The major symptoms are brown spots on the leaves, stem, petals and sepals resulted in premature defoliation and leads to death of the plant under severe infection (Anilkumar et al., 1974). It also affects the formation of number of seeds per head, seed filling, kernel weight and oil content. Cloudy weather, high humidity and drizzling rains can result in severe outbreak and spread of the disease. As there is no resistant variety available for this disease, it is essential to use the fungicides to manage this disease. Many commonly used fungicides such as vitavax, captan, dithane Z-78, fytolan, thiride and benlate failed to provide satisfactory control of severe incidence of leaf blight under field conditions, especially during the rainy season (Mukewar and Gera, 1980). Hence, this experiment was taken up with combi fungicides to find out new effective  and cheaper fungicides for management of this disease. 

The experiment was carried out at the farm of Regional Agricultural Research Station, Nandyal (15 27N and 78 28E) of Andhra Pradesh for three years from kharif, 2018 to 2020 under All India Coordinated Research Project on sunflower scheme (Anonymous, 2018a). The soil of the experimental field was black cotton, with pH 8.3 and EC 0.26 dS/m. The experiment was laid out in Randomized block design with susceptible check  KBSH-44, with six different fungicides (combi products) and one untreated control was maintained in three replications. Susceptible check seed was obtained from IIOR, Hyderabad. The fungicide  SAAF (carbendazim 12%+mancozeb 63%)  was used for all the treatments except untreated plots as it is a seed borne pathogen. Plot size of 4.2×3 m² and spacing of 60x30 cm  were maintained for all the treatments.  Regular agronomic practices were followed as per the technical programme of work. All the treatments were imposed for two times as per the schedule given i.e., first spray was done at the time of disease initiation and second spray was done at 15 days after first spray.  Disease scoring was done randomly on ten selected plants from each plot at 15 days interval based on 0-9 scale (Anonymous, 2018b), which was commonly followed for Alternariaster leaf spot.
0- No symptoms on the leaf.
1- Small, circular, scattered brown spots covering 1% or less of the leaf area.
3- Spots enlarging, dark brown in colour covering 1-10% of leaf area.
5- Spots enlarging, dark brown in colour, target like appearance covering 11-25% of leaf area.
7- Spots dark brown, coalescing with target like appearance covering 26-50% of leaf area.
9- Spots uniformly dark brown, coalescing covering 51% or above of leaf area.
       
From the collected data, per cent disease index (PDI) was calculated by using the below formula (Mayee and Datar (1986). 
         
After harvesting data pertaining to seed yield was recorded. Data was analysed statistically by ANOVA. The B:C ratio was calculated by deducting the cost of cultivation from gross returns and the result was divided by gross returns for the data in pooled analysis.

During kharif 2018 the treatment T₃: (Seed treatment with carbendazim 12% + mancozeb 63% WP @  2 g/kg seed followed by two foliar sprays with Trifloxystrobin 25%+ tebuconazole 50% (Nativo 75 WG) @ 0.25 g/l) has given less PDI of Alternaria leaf spot  i.e., 24.68 % and also recorded higher yields  of 1743 kg/ha (Table 1). It was followed by T₁ (Seed treatment with carbendazim 12% + mancozeb 63% WP (SAAF 75 WP) @  2 g/kg seed followed by two foliar sprays with difenconazole 25% + propiconazole 25% (TASPA 500EC) @ 0.3 ml/l), T₄(Seed treatment with carbendazim 12% + mancozeb 63% wp @ 2 g/kg seed followed by two foliar sprays with pyraclostrobin 5% + metiram 55% (Cabriotop 60WG) @ 0.3g/l), T₅(Seed treatment with carbendazim 12% + mancozeb 63% wp @  2 g/kg seed followed by two foliar sprays with tricyclazole 18%+mancozeb 62% (Merger 80 WP) 1 g/l) and T₂ (Seed treatment with carbendazim 12% + mancozeb 63% wp  @  2 g/kg seed followed by two foliar sprays with zineb 68% + Hexaconazole 4% WP @ 2.5 g/l) treatments recorded  the disease severity of  28.82%, 30.1%, 30.29%  and 31.17%, respectively and which were at par with T₃. Control or untreated plot recorded highest disease severity (PDI) of 35.95% and  it was non significant with disease severity in T₆(Seed treatment with carbendazim 12% + mancozeb 63% wp @ 2 g/kg seed followed by two foliar sprays with mancozeb 75 WP @ 2.5g/l  followed by two sprays  2g/kg seed followed by two foliar sprays) treatment. During kharif 2019, the treatment T₃ has given less PDI of Alternariaster leaf spot i.e., 36.71% and also recorded higher yields of   1567 kg/ha. It was followed by the treatments  T₂, T₁, T₄ and T₅ that recorded the disease severity of 40.57%,  43.79%,  45.58% and 47%, respectively which were non significant  with each other and significant over control and T₆. The highest severity of disease (66.71%) was observed  in control plot. During 2020 also the same treatment T1 performed better in disease reduction compared to other treatments. Similarly other treatments i.e., T₃, T₂, T₅ and T₄  recorded less disease severity  respectively and non significant  with each other.  Control has recorded  more  Alternariaster leaf spot (PDI) of 67.02%.
 

 
Yield
 
In 2018, the treatment T₃ has recorded significantly higher yield of 1743 kg/ha over control and the treatment T₆ and it was non significant with other treatments (Table 1). The next higher yield was obtained in the treatment T₁ i.e., 1680 kg/ha, whereas control has recorded low yield of  1516 kg/ha. During 2019 also, higher yield was obtained in the treatment T₃ which recorded significantly higher  yield over control  i.e., 1567 kg/ha  and non significant with other treatments i.e., T₂, T₁, T₄ and T₅. But during 2020, the treatment T₁ recorded  higher  yields of 888 kg/ha than T₃ and it was significant  over control  i.e., 747 kg/ha, however, it was non significant with all other treatments.  
       
In the experimental period of three years, low disease pressure was observed in the year 2018 compared to other two years i.e., 2019, 2020 and slightly higher disease pressure was observed in 2020 than 2019. This might be due to weather conditions prevailed in the respective years. During the crop season of 2018, a total rainfall of 150.4 mm (From July II FN to October II FN), the minimum and maximum temperature recorded more or less of 25°C and 35°C, respectively. The RH-I was not more than 80% (71.4 to 81%) and RH-II (41.1 to 48.1%) was also <50% in majority of meteorological weeks (weather data enclosed). For the same period during 2019, total rainfall of 778.4 mm, minimum temperature in the range of 23.9 to 25.5°C,  maximum temperature in the range 29.4 to 34.7°C and RH-I (80.7 to 91.6%), RH-II (52.6 to 74%) for same  meteorological weeks were recorded during 2020, a total rainfall of  896.8 mm received, minimum temperature of 24.1 to 25.8°C, maximum temperature of 29.4 to 34.3°C and RH-I (77-92%), RH-II (64 to 82%) of meteorological weeks. According to Venkataramana et al., (1995) temperature in the range of 25°C-27°C with at least 12 hours of wet foliage helps to spread rapidly during the rainy season. The rainfall along with heavy dew deposition provided wetness on leaves for about 14-15 h day. Borkar and Patil (1995), observed that temperature of 25.9°C to 33.7°C, relative humidity of 89-95% favoured Alternariaster leaf spot disease development. Rainfall had significantly positive effect on disease development. Hiremath et al., (1990) reported that, higher rainfall had positive influence on Alternariaster blight of sunflower. The species of A.helianthi was reported to be at its peak in growth and sporulationunder high relative humidity of 89-95 per cent (Patil, 1989). More or less the same weather conditions prevailed in the experimental years of 2019 and 2020 i.e., high rainfall, high RH-I and RH-II, moderate temperatures compared to 2018, hence the disease appeared  in severe form. When compared to 2019,  the climate was more congenial for  development of Alternariaster leaf spot in 2020, hence more disease was recorded.
       
Regarding yield, more was found in 2018 and 2019 compared to 2020. In 2018, though less rainfall was received higher yield was obtained. Because two life saving irrigations were given at times in need and also less disease was recorded. Whereas  in 2020,  for the period of six weeks  (from 37 to 42 MW), heavy rainfall of 574.6 mm  rainfall was received and the crop was in flowering to seed setting stage and the crop was suffered from heavy moisture stress. Because of heavy moisture in soil, the roots were unable to absorb nutrients from soil, hence low yields resulted. This was  in conformity with  Orchard et al., (1986) who suggested that water logging during vegetative and flower initiation stages inhibited expansion of leaf  and at anthesis stage reduced yields  were noticed by Orchard and Jessop (1984). Grassini et al., (2007) reported decreased grain yields and adverse physiological responses were due to the effect of water logging conditions in sunflower crop. Hence, in the present experiment,  in the experimental year, 2020 yields were  reduced drastically. 
       
Pooled analysis results (Table 2) indicated that among the seven treatments, the treatment T₃:  (Seed treatment with carbendazim 12% + mancozeb 63% WP (SAAF 75 WP) @ 2 g/kg seed followed by two foliar sprays with Trifloxystrobin 25%+ tebuconazole 50% (Nativo 75 WG)@ 0.25 g/l) was recorded low severity of Alternariaster leaf spot i.e., 37.0% with 30.68 % of disease reduction over control. It is followed by T₁, T₂, T₄, T₅ which recorded disease severity of  40.95%,  42.47 %, 45.38% and 45.76% respectively and all these treatments were at par with each other.  Control or untreated plot (T₇) recorded  more disease severity of  53.38% and T₆ recorded disease severity of 49.37% and both were non significant with each other.
 

       
In terms of yield also the same treatment T₃ has recorded higher yield of 1382 kg/ha and it was at par with all other treatments except T₆ and control. Control or untreated plot recorded lower yield of 1200  kg/ha. Regarding B:C ratio, the treatment T₁  has recorded higher B:C ratio of 1.65, compared to T₃ (1.57), as the chemical (trifloxystrobin 25%+ tebuconazole 50%) was costlier than others. Treatment T₁ recorded B:C ratio of 1.65 followed by T₄ recorded i.e., 1.59,where as check recorded B:C ratio of 1.55, respectively.
       
Seed treatment with fungicides protect the seeds from seed borne infections as it is a seed borne pathogen and it also helps in seed germination. Present experimental results are in conformity with the same experiment conducted at AICRP on Sunflower scheme at Ludhiana cnetre also, where the same treatment i.e., T₃ recorded low disease severity (PDI) of 11.8% with higher yield of 2454 kg/ha followed by T₁ which recorded PDI of 15.9%, with yield of 2292 kg/ha, whereas control recorded 37.5% with low yield of 1627 kg/ha. At Bengaluru centre also, the treatment T₁ recorded low disease severity (PDI) of 14.8% with higher yield of 2032 kg/ha, followed by T₃ and recorded disease severity of 18%, higher yield of 2033 kg/ha compared to control, which recorded PDI of 41.8% with low yield of 1584 kg/ha (Anonymous, 2021-22). Venkataramanamma et al., (2014)  conducted an experiment on management of Alternaria leaf spot disease of sunflower with five different fungicides and found that the treatment T₃ (seed treatment with SAAF @ 2 g/kg of seed followed by two foliar sprays of propiconazole @ 1 ml/litre at 15 days interval starting from the appearance of disease) has recorded least per cent disease intensity of 12.23% with higher yield 918 kg/ha when compared to control, which recorded more disease severity (PDI) of 60.2% with low yield of 542 kg/ha and they used SAAF as the seed treatment chemical. Similarly, Waghe et al., (2015) has conducted a management trial on Alternariaster leaf spot disease under in vivo conditions and among eight treatments imposed, the treatment i.e., seed treatment with fungicide (carbendazim 12% + mancozeb 63%) @3 g/kg seed + two sprays of (carbendazim 12% + mancozeb 63%) @ 0.2% at 30 and 45 DAS recorded higher disease control (82.82%) with good seed yield (16.86 q/ha).The effectiveness of propiconazole  and other triazoles on Alternariaster leaf spot of sunflower was reported by Mane et al., (2019) and Mesta et al., (2011). Similarly in the present experiment also, the treatments i.e., T₃ and T₁ performed better when compared to others. However,T₄ recorded higher B:C ratio than T₃ because of its low cost.

Hence, from this experiment it can be concluded that, among the seven treatments, the treatment  T₃(Seed treatment with carbendazim 12% + mancozeb 63% WP (SAAF 75 WP) @  2g/kg seed followed by two foliar sprays with (Nativo 75WG)@ 0.25g/l) and  T₁(Seed treatment with carbendazim 12% + mancozeb 63% wp (SAAF 75 WP) @  2 g/kg seed followed by two foliar sprays with difenconazole 25% + propiconazole 25% (TASPA 500EC) @ 0.3 ml/l) may be recommended. Though the treatment T₄(Seed treatment with carbendazim 12% + mancozeb 63% WP @2 g/kg seed followed by two foliar sprays with pyraclostrobin 5% + metiram 55% (Cabriotop 60WG) @ 0.3 g/l) recorded higher PDI than T₁, T₃ and T₂ it may also be recommended as it recorded more B: C ratio compared to T₂ and T₃.

Authors are thankful to Indian Institute of Oilseeds Research, Hyderabad and Acharya N G Ranga Agricultural University for providing research facilities.

None.