2.1. Experimental Site and Land Preparation The experiment was conducted in the Botanical Pesticide Experimental Field of Institute of Environmental Science, University of Rajshahi, Bangladesh during November 2019 to February 2020. The land was firstly ploughed several times with spade, and grass, weeds etc. are removed after each ploughing. A recommended amount of Cow-dung, Triple super Phosphate (TSP), Muriate of Potash (MP) and Urea fertilizers were applied in the experimental field.The field was irrigated two times after sowing.
2.2. Collection of Botanicals Botanicals were collected considering the following properties: odour, anti-fungal activity, phyto-toxicity. Results of previous studies and ethno-botanical knowledge were also kept in mind at the time of plant selection. Most of the selected plant materials were collected from the Rajshahi University campus and some were purchased from local market.
2.3. Preparation of Botanical Extracts Collected botanicals were washed through running tap water 2-3 times. After washing the botanicals were dried under shed for 2/3 weeks. Dried materials except garlic grinded with the help of electric grinder to make fine powder (Khair and Haggag, 2007; Majeed et al., 2011; Azad et al., 2013). 25g of fine powder of each plant materials were dissolved separately in 1000 ml of distilled water in plastic container. In case of garlic, bulbs were cut into small pieces and blended by blender. About 25g of blended garlic dissolved in 1000 ml of distilled water in a plastic container. The containers were kept in room temperature for 72 hours and the mixture was shake gently every day. After 72 hours, the mixture was filtered through three-layer cheesecloth to collect the plant extracts of 2.5% concentration (w/v). The extracts were kept in bottle and preserve in the refrigerator for future use.
2.4. Experimental Design and Treatments The experiment was laid out in completely randomized block design (CRBD) with three replications. The distance between the block was 1m and between the plots was 0.5 m., the unit plot size was 1m × 1m. Twelve treatments were used in this study including two controls (one untreated and one Chemical treated) and ten plant extracts.
2.5. Botanical Extract Spray Prepared botanical extracts were sprayed in the field with a hand sprayer to potato leaves twice weekly started at 30 Days after sowing (DAS). Data on disease incidence and severity was collected at 7-day interval on 50, 58, 66 and 73 DAS.
2.6. Disease Assessment and Yield Calculation Disease incidence and severity is expressed in percentage following the formulas bellow (Islam et al., 2013)
Disease incidence (%) = No.of diseased plants / Total no.of plants observed x 100
Severity (%) = No. of blighted leaves per plantlet / Total no. of leaves per plantlet x 100
After harvesting total tuber yield (kg /plot) were calculated by collecting and weighing tubers from each experimental plot and percent yield increase over control was calculate through following formula(Ray et al., 2018)-
Yield increase (%) = Treatment yield−Control yield / control yield x 100
2.7. Data Analysis The collected data were analyzed statistically using analysis of variance (ANOVA) to find out the variations among the treatments and treatments means were compared by DMRT using software SPSS (V20).