Downy mildew is a plant pathogen that causes downy mildew on crops such as cucumber, melon, squash, watermelon, and squash that belong to the Peronosporaceae family. The biological causative agent is the obligate parasitic plant cubensis. The causative agent is resistant, persists in infected plant debris, surviving in cold weather. In spring, at a temperature of 59-68 °F (15–20 °C), infected seeds germinate, from which zoospores emerge, which spread to healthy plants. In most cases, the disease occurs in poorly ventilated and damp conditions. Factors such as sudden fluctuations in ambient temperature and heat can also provoke the rapid development of this disease in plants.