Efficacy of fungicides against powdery mildew of cucumber (Cucumis sativus L.)

Introduction

A member of the Cucurbitaceae family, cucumber (Cucumis sativus L.) is one of the earliest vegetable crops to be produced. Vegetables like cucumber are widely grown. The plant is a creeping vine that produces cucumiform blossoms, which can be eaten raw or cooked. Pickling, seedless, and slicing are the three main types of cucumbers. Fruits are good for people suffering from constipation, jaundice, and indigestion (Anonymous, 2014) [2] . The primary objective of cucurbitaceous vegetable research in India is to generate biotic and abiotic-resistant varieties and hybrids with excellent qualities in order to increase productivity on a sustainable basis (Rai et al., 2008) [15] . Powdery mildew is an important disease of cucurbits, particularly cucumber, which is highly susceptible to this disease and suffers heavy losses in all localities of Maharashtra State, wherever it is grown. In the Maharashtra districts of Aurangabad and Jalana, the incidence of disease was found to range from 20.10% to 47.28% on various cultivars. (S. M. Wahul, 2018) [18,19] . Cucumber powdery mildew disease is attributed to two fungal species, Sphaerotheca fuliginea (Schltdl.) Pollaci and Erysiphe cichoracearum (DC.), which belong to two different genera in the same family, Erysiphaceae. Yield loss due to powdery and downy mildew diseases was estimated to be 50-70 percent. Though there are many cultural practices employed, such as crop rotation and fall ploughing, and also the use of fungicides, crop loss was reported to be 50-70 percent. The severity and disease development in cucurbits have led to severe yield losses; hence, a detailed study to assess the efficacy of systemic fungicides and combi fungicides under in-vitro and in-vivo conditions is very important.

Materials and Methods

Fungicides

The following fungicides which is effective against powdery mildew of cucumber were used with their recommended doses. The fungicides require for the present investigation were provided by Department of Plant Pathology, College of Agriculture, Nagpur (MS).

Layout and plan

The field experiments were conducted in Randomized Block Design (RBD) with seven treatments and three replications and laboratory experiment was also conducted with Randomized Block Design (RBD) with seven treatments and three replications. In each plot five cucumber plants were randomly selected and for measuring disease intensity, lower, middle and upper crop canopy observed and evaluated individually using 0-9 rating scale based on leaf area covered by pustules as mentioned below.

Detail of layout

Rating scale used for disease intensity (Mayee and Datar, 1986) [12] Rating scale Description 0.

1.

Powdery mildew pustules small, scattered covering 1% or less of leaf area.

3.

Powdery mildew pustules more in number covering 1-10% of leaf area.

5.

Typical powdery mildew pustules covering 11-25% of leaf area.

7.

Typical powdery mildew pustules covering 26-50% of leaf area.

9.

Typical powdery mildew pustules covering 51% or more of leaf area.

Plate 1: Disease scoring scale for powdery mildew of cucumber Further these scales were converted to percent disease intensity using following formula. (Mc Kinney, 1923) [11] Sum of observed numerical rating 100 PDI = x Number of leaves x plant observed Maximum rating Further, percent disease control (PDC) was worked out by applying the following formula.

PDI in control plot -PDI in treatment plot PDC =

Effect of fungicides on inhibition of conidial germination of E. cichoracearum In-vitro

The efficacy of six fungicides at double concentrations (0.2%) was tested against E. cichoracearum by spore germination technique. Required concentration of each fungicide was prepared in distilled water. Two drops of fungicide solution were taken on clean cavity slide. Powdery mildew spores were suspended using camel hair brush in fungicide solution on the cavity slide. Each concentration was replicated thrice in a separate cavity slide. Control treatment was maintained by putting conidia with distilled water. These cavity slides were kept in the Petri plates lined with moist blotting paper and were incubated at room temperature (28 ± 1 °C) for 24 hours. After 24 hours, observations were taken at 40 X microscopic fields for each cavity slide, the total number of spores and germinated spores in each microscopic field were recorded and percent germination and percent germination inhibition was calculated. Percent germination was calculated by counting number of conidia germinated against total number of conidia observed microscopic field at magnification of 40 X by using the formula mentioned below. Observations were recorded at 7 days interval of meteorological week by using 0-9 scale (Mayee and Datar, 1986) [12] . The data of these weather parameters was collected from Agro Meteorological Division of College of Agriculture Nagpur. The disease development was correlated with weather parameters viz., rainfall, maximum and minimum temperature, relative humidity during morning and evening on cucumber crop.

Results and Discussion

Evaluvation of fungicides against conidial germination of Erysiphe cichoracearum In-vitro

Six systemic fungicides were tested under in-vitro conditions at room temperature against E. cichoracearum for inhibition of conidial germination and the results are presented in Table 1. No conidial germination was observed in azoxystrobin 23% (0.2%), carbendazim (0.2%), propiconazole (0.2%), azoxystrobin 4.8% w/W + chlorothalonil 40% w/W (0.2%), fluxapyroxad 250 g/l + pyraclostrobin 250 g/l SC (0.2%). The treatment metrafennone 500 g/SC (0.08%) were showed germination (12.97) percent. The maximum conidial germination was observed in control (39.36) percent.Maximum conidial germination inhibition (100%) was observed in azoxystrobin (0.2%), carbendazim (0.2%), propiconazole (0.2%), azoxystrobin 4.8% w/W + chlorothalonil 40% w/W (0.2%), fluxapyroxad 250 g/l + pyraclostrobin 250 g/l SC (0.2%). The treatments of metrafennone 500 g/SC (0.08%) showed conidial germination inhibition (66.73) percent.

Average effect of fungicidal spraying on Percent disease intensity of powdery mildew and percent disease control

The results of the average percent disease intensity and percent disease control after each spraying have been summarized in table 2. and final effect of different treatment on percent disease control in relation to percent disease intensity is represented graphically in fig. 2. From the table 2 it was indicated that, all the treatments were significantly superior over untreated control in reducing the disease intensity of powdery mildew of cucumber. The minimum Percent disease intensity (PDI) was noticed in treatment azoxystrobin 23% (0.1%) which was highly significant among all the treatments. The next best treatment was propiconazole (0.1%) which is also superior to remaining treatments recording (19.01) and (22.22) percent disease intensity respectively. The other promising treatments were fluxapyroxad 250 g/l + pyraclostrobin 250 g/l SC (0.1%) and azoxystrobin 4.8% w/W + chlorothalonil 40% w/W (0.1%) recording (27.89) and (28.93) percent disease intensity respectively. The next promising treatments were carbendazim 50% WP (0.1%) and metrafennone 500 g/SC (0.04%) exhibiting (34.11) and (36.91) percent disease intensity respectively. Maximum Percent disease control (PDC) was observed in treatment azoxystrobin 23% (0.1%) followed by propiconazole (0.1%) and fluxapyroxad 250 g/l + pyraclostrobin 250 g/l SC (0.1%) recording (67.72), (62.42) and (52.66) percent respectively.

From The table 5 it was also indicated that among the fungicides evaluated, three sprays of azoxystrobin 23% (0.1%) resulted in maximum fruit yield (80.00 ql/ha) which was followed by propiconazole (0.1%) (70.00 ql/ha) and fluxapyroxad 250 g/l + pyraclostrobin 250 g/l SC (0.1%) (67.65 ql/ha) respectively.

Correlation of weather parameters with Percent disease intensity of powdery mildew of cucumber during rabi season 2023

The data were analysed by statistically and presented in Table 3. Concluded that the powdery mildew was appeared in 44 th (MW) and it was spread upto 51 th (MW). Highest intensity of powdery mildew was noticed in 51 th (MW) exhibiting 79.13 percent disease intensity.

Maximum temperature (-0.729) had showed highly significant and negative correlation with powdery mildew, while minimum temperature (-0.603) showed highly nonsignificant and negative correlation with percent disease intensity of powdery mildew. Whereas Relative humidity during morning (0.351) and evening (0.346) and also rainfall (0.152) had shown moderately non-significant and positive correlation with percent disease intensity of powdery mildew of cucumber.

Conclusion

It is concluded from the present study evident that all the fungicides were effective in reducing disease intensity over control. Among the foliar spray of fungicides azoxystrobin 23% (0.1%) was most effective than other fungicides in reducing the percent disease intensity of powdery mildew and increasing yield followed by propiconazole (0.1%).

Azoxystrobin (0.2%), carbendazim (0.2%), propiconazole (0.2%), Azoxystrobin 4.8% w/W + Chlorothalonil 40% w/W (0.2%), Fluxapyroxad 250 g/l + Pyraclostrobin 250 g/l SC (0.2%) were found effective and recorded significantly highest inhibition of conidial germination (100) percent of Erysiphe cichoraciarum.

Weather parameters like temperature and relative humidity plays an important role in development of the powdery mildew of cucumber.

Acknowledgements

I am thankful to the Head of the Plant Pathology section, College of Agriculture, Nagpur for providing all the necessary facilities for conducting the research work.

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