Anthracnose is a common disease among deciduous trees especially sycamore ash and oak it also affects shrubs such as privet it causes unsightly dark sunken lesions on leaves stems flowers and fruits anthracnose fungi need water to spread and infect so the disease is more prevalent during wet cold springs. Many plant diseases can quickly return if the dead plant matter isnt properly disposed of in fact most fungal bacterial and viral plant diseases are spread naturally by wind currents rain soil seeds insects and other animals others can survive on nearby dead plants or infected gardening tools. Although it would seem like a no brainer to assume that plant and human diseases are distinct and cannot crossover from plant to gardener this isnt the case at all human infection from plants is very rare but it does happen the primary pathogen of concern is a bacteria known as pseudomonas aeruginosa which causes a type of soft rot in plants p aeruginosa infections in humans can . Leaf spot diseases weaken trees and shrubs by interrupting photosynthesis most leaf spot diseases affect only a small percentage of the trees overall leaf area and are a minor stress on the health of the tree leaf spot diseases should be taken seriously if they result in moderate to complete leaf loss two to four years in a row