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Maize an important staple food crop affected by number of diseases during its growth stages, besides, turcicum leaf blight (Exserohilum turcicium) is one of the most important diseases with 98 per cent losses in Karnataka. Soybean rust incited by Phakopsora pachyrhizi is one of the most serious disease inflicting quantitative as well as qualitative losses. The disease is more severe under assured rainfall and irrigated conditions with moderate temperatures and extended leaf wetness. With the introduction of high yielding genotypes, extensive use of fertilizer, traditional irrigation management practices and continuous cropping system, there has been a phenomenal increase in incidence of diseases in various cropping system.

Besides, conservation agriculture principles and practices i.e. minimum and zero tillage, use of preceding crop residues to protect soil and water in succeeding crops and cropping system i.e. Cereal – Legume sequence cropping lead to further variation in diseases. Hence, present study was conducted to know the occurrence of diseases under the prevailing conditions.

MATERIALS AND METHODS

Investigations were carried out in Maize (Zea mays L.) – Soybean (Glycine max L.) at Main Agricultural Research Station, Dharwad on clayey soil. Initial soil sampling of experimental plot recorded pH (7.4), EC (0.23 dS/m), organic carbon (0.55), available N (250 kg ha-1), available P2O5 (33 kg ha-1), available K2O (290 kg ha-1), exchangeable Ca (28 cmol (p+) kg-1), exchangeable Mg (7 cmol (p+) kg-1) and available S (21 kg ha-1). Maize were evaluated with irrigation and fertilizer management practices under minimum tillage during summer (2012-13 and 2013-14), followed by Soybean as residual crop under zero tillage in Kharif season (2013-14 and 2014-15). Experiment was laid out in split split plot design with irrigation levels in main plots, fertilizer levels and its application rate in sub plots with three replications. Irrigation levels were deficit irrigation at growth stages (I1), I1 + hydrogel with 2.5 kg ha-1 (I2) and alternatively alternate furrow irrigation at 50 per cent depletion of soil moisture (I3). Fertilizer levels were as F1 - 200:75:75 kg N:P2O5:K2O ha-1 (2.67:1:1), F2 - 225:100:100 kg N:P2O5:K2O ha-1 (2.25:1:1) and F3 - 250:100:125 kg N:P2O5:K2O ha-1 (2.5:1:1.25). Fertilizer applications were T1 - 25 per cent (1/4th) of N, K2O and 50 per cent of P2O5 as basal, 50 per cent of N, P2O5and K2O at 30 DAS and 25 per cent of N and K2O at 50 DAS and T2  - 33 per cent each (1/3rd) of N, P2O5 and K2O as basal, 33 per cent each of N, P2O5 and K2O at 30 DAS and 33 per cent each of N, P2O5 and K2O at 50 DAS in sub plots. Besides, control outside the design i.e., Conventional furrow irrigation and fertilizer levels of 150:75:37.5 kg N:P2O5:K2O ha-1 (4:2:1) and its applications as 15 kg N plus full dose of P2O5 and K2O as basal, 30 kg N at 20 DAS, 45 kg N each at 35 and 50 DAS and 15 kg N at 65 DAS). MgSO4 (10 kg ha-1) and gypsum (250 kg ha-1) were amended for all treatments, except control and data were analyzed as per Gomez and Gomez (1984). Five Maize plants were randomly selected for recording the diseases severity based on 1 to 5 rating scale (Laxminarayan and Shankarlingam, 1983). Further, Per cent Disease Index was calculated as per Payak and Sharma (1983) and transformed to reduced the variation. Besides, the trifoliate soybean leaves from middle portion of the plants were randomly collected and assessed for rust severity using 0 to 9 scales of Mayee and Datar (1986) and Per cent Disease Index was calculated by using the formula of Wheeler (1969), further data was transformed for analysis.

RESULTS AND DISCUSSION

Turcicum leaf blight in Maize
Effect of irrigation and fertilizer management practices differed significantly at 60 and 90 days after sowing on turcicum leaf blight (Table 1). Alternatively alternate furrow irrigation, fertilizer levels of 250:100:125 kg N:P2O5:K2O ha-1 (2.5:1:1.25), scheduling of fertilizers as 33 per cent each (1/3rd) of N, P2O5 and K2O as basal, 33 per cent each of N, P2O5 and K2O at 30 DAS and 33 per cent each of N, P2O5 and K2O at 50 DAS and its interaction recorded higher severity of diseases (27.91, 27.55, 27.77 and 30.57 per cent, respectively) at 90 days after sowing when compared to other treatment combinations. Similar trend were recorded at 60 days after sowing. Scheduling alternatively with higher depth of irrigation and higher nutrients with staggered application during crop growth period changed micro climate of maize crop in lower layers, higher temperature during summer, higher relative humidity, along with occasionally higher rainfall favored higher incidence and multiplication of diseases from lower leaves to upper leaves. Besides control recorded diseases severity of 26.58 per cent at 60 and 90 days after sowing. Similar research findings were also recorded by Chandrashekara et al. (2014), Dalavai and Kalappanavar (2017), and Patil and Motagi (2020).
Leaf rust in Soybean
Residual effect of irrigation and fertilizer management practices on leaf rust differed significantly at 45 days after sowing and harvest (Table 1). residual effect of alternatively alternate furrow irrigation, fertilizer levels of 225:100:100 kg N:P2O5:K2O ha-1 (2.25:1:1), fertilizer applications as 25 per cent (1/4th) of N, K2O and 50 per cent of P2O5 as basal, 50 per cent of N, P2O5and K2O at 30 DAS and 25 per cent of N and K2O at 50 DAS and its interaction observed significantly higher severity of diseases (3.25, 2.26, 3.17 and 9.26 per cent, respectively) at harvest when compared to other treatments. Similar results were recorded at 45 days after sowing. Delayed sowing, high weed intensity under zero tillage, left over maize residues, fallow knock down weeds after maize, high relative humidity, optimum temperature and intermittent rainfall in early stage favored uredospore germination. Whereas, low humidity, high temperature and high rainfall in later stage of crop favored higher multiplication of rust. Further, control plot there was no disease incidences. Similar research findings were also recorded by Sarnobat et al. (2019), Shamarao Jahagirdar (2019) and Sharadha et al. (2020).

CONCLUSION

Higher depth of irrigation and fertilizer levels with its staggered applications favored higher diseases severity in Maize and Soybean sequence cropping under conservation agriculture.

REFERENCES

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Wheeler, B. E. J. (1969). An Introduction to Plant Diseases. John Wiley and Sons Ltd., London, p. 301.