Leaves are getting like this.

Hi Shakti Prasad Binayak . Remove weeds in and around from the field or plant guarden. As per this image, its showing symptoms of Tobacco Caterpillar effect. Click on green link for checking symptoms and taking control measures from Plantix library. Care: Don't do over irrigation. Don't allow soil to become water logged. Apply good amount of Farm Yard manure or Vermicompost along with recommended dosage of fertilizers or use cucumber fertilizer calculater available here on home page of Plantix to get good growth of your plant.