A Polyethylene tarp used for the crosswalk inside the greenhouse; it protects the field from weeds and contamination from other agents in the soil, such as nematodes and diseases. These covers may be white or black and white and its measurements may go to 8 meters (26 feet) wide and 50 to 100 meters (164 to 328 feet) long, with a 250 to 375 µ (10 to 15 mils).