so i want to know If this can reduce the production of resin

your plant needs the uv light rays to grow, as far as trying to stop the production of resin, why? all plants will have some form of resin, it is nature and how the plants grow, so if your not looking for resin, then maybe a nice cbd strain? that will have resin too, resin is good esp. in cannabis

Your plant will need UV light for it to make complete cannabinoids. Rain during vegetative growth won't hurt it, only towards the end of flowering is rain likely to cause problems. There are types of plastic sheeting for greenhouse use that don't block UV light and this would be far better to use. Tell the store you are growing tomatoes. Otherwise you could grow them in pots and move them under shelter when rain is forecast or only put up the "tile" when rain is due, leaving the plant in full sun for the rest of the time. A few days under the UV blocking "tile" shouldn't effect resin quality greatly, but having it under the UV blocking "tile" for its entire growing and flowering cycle will lead to incomplete photosynthesis, affecting both growth and resin quality. Hope this helps,....... Organoman.