Which method is NOT effective in controlling the spread of black knot?

Regular irrigation does not effectively control the spread of black knot, which is a fungal disease affecting various trees, particularly plums and cherries. While proper irrigation is essential for general plant health, it can inadvertently create conditions that promote fungal growth if not managed correctly. Overly moist environments can lead to increased humidity and leaf wetness, both of which favor the development and spread of black knot spores.

In contrast, pruning infected limbs directly removes the source of the fungus, helping to prevent its spread to healthy parts of the plant. Maintaining overall plant health contributes to stronger plants that can better resist diseases, including fungi like black knot. Planting resistant species can be the most proactive approach to avoiding the disease altogether, as these varieties are bred to withstand infections. Thus, while regular irrigation is important for plant health, it does not play a direct role in controlling the spread of black knot.