About the Disease: This disease is mainly seen in the pumpkin crops. The amount of damage that is caused due to this disease cannot be clearly measured. The yield loss can be very high at times. This mainly happens in the Mid West region.
Symptoms: There are pale green spots on the top portion of the leaf. These will later get converted into brown color. All the spots are bounded by the veins of the leaf. In cucumber plants, it is clearly seen.
Pathogen involved: Pseudoperonospora cubensis is the main causative agent. This is actually an oomycete and is not considered to be a true fungus. It is also called as the water mold. This disease can affect cucumber, melon varieties, pumpkin as well as squash.
Time of Occurrence: This mainly occurs in a cool and wet climate.
Conditions Favoring Disease: The main environmental factors that might favor the growth of the disease are the cool weather. When the weather is always wet as well as cool, you can expect the plants to get affected by this disease. Such a weather condition is considered to be a real threat for plants in the later part of the growing season.
Disease Management: There are three main ways of controlling the disease. The chemical method involves the use of proper fungicides. These fungicides must exclusively kill only the fungus causing the disease and not the entire plant or the adjacent plants. There are two main types of fungicides, the broad spectrum and the systemic fungicides. The systemic ones will be used only for this disease. It can be used only after you have thoroughly examined the plant and confirmed that it is affected by this disease.
But the broad spectrum fungicides like chlorothalonil and Mancozeb are effective against many diseases. Sometimes when you grow the resistant varieties, that are not susceptible to this disease, you can easily save all the crops. Such resistant varieties can be found in the pumpkin plants. The third and an easy method is by changing the culture methods. Sometimes, when you grow the same diseased plant continuously, in the same area, then it is not possible to completely get rid of that disease. The disease will keep appearing every now and then. Thus the best way to avoid the disease or to manage the disease is to start crop rotations. If you are growing cabbage for a year, you can grow pumpkin in the next year. The tillage practices can be changed.