This disease appears to be more important each year. It is not clear to me why. This article reviews Plectosporium of pumpkin, sometimes called white speck.
I would rank Plectosporium blight behind powdery mildew, bacterial leaf spot and Phytophthora blight in economic damage caused. The occurrence of this disease is usually sporadic. However, when it occurs, it can cause yield loss if left uncontrolled. Plectosporium blight can be recognized from the light tan spindle shaped lesions on stems and leaf petioles (Figure 1).
Lesions on leaves may be dimple like. Lesions may also occur on the fruit (Figure 2), although these symptoms are less common. Yield loss is most often caused by lesions on the stem adjacent to the fruit—the pumpkin handle (botanically known as the peduncle). Yellow squash and zucchini squash are also affected. When lesions occur in large numbers they can give a light gray or white appearance to the foliage. Usually, the lesions affect only the appearance of the foliage or fruit. Infrequently, the lesions can become so severe on young plants that individual leaves or vines may wilt. This disease may be managed through a combination of cultural and fungicide treatments. Crop rotations of 3-4 years and fall tillage will help keep the crop residue to a minimum. A regular contact fungicide program will also help to keep Plectosporium blight in check. My understanding has been that any fungicide program that includes products labeled for Plectosporium on pumpkin will be effective. However, given the disease severity growers have experienced recently, I especially recommend group 11 products: Flint®, Cabrio®, Pristine®, Merivon® and Quardis® including Quadris Top®.
Figure 1. Plectosporium blight on pumpkin stem.
Figure 2. Plectosporium blight on pumpkin fruit and handle.