The curly willow is a fast-growing tree with an upright frame that reaches mature heights of up to 30 feet. A shade tree, the curly willow, or corkscrew willow, produces strong, upright branches with long, pendulous stems filled with long, alternating foliage. It thrives in well-drained soils and has a high salt tolerance. Though hardy, the curly willow tree is susceptible to several diseases, some of which can be harmful when left untreated.
Crown gall is a bacterial disease that is transported through spores. This disease attacks the curly willow tree through open wounds in its woody area. This infectious bacterium attacks the willow's vascular system and slows the tree's transport of water and nutrient. The tree develops rough galls around the base and trunk of the tree, as well as on its branches and stems. Galls also appear on and near the areas where the bacteria entered the tree. The infected willow experiences growth stunt and dieback from the lack of nutrients, which also results in increased winter injury and premature defoliation. Infected areas must be removed from the tree with sharp, sterile shears that are sterilised between each cut. This will prevent spreading the disease throughout the tree. Severely infected curly willow trees must be removed and destroyed to prevent spreading the disease to other trees.
Powdery mildew is a fungal disease that infects the young foliage of the curly willow. The infected curly willow will generally display signs of infection during the early fall. The infected foliage develops powdery white coverings of fungus, which cover the small, decaying circles on the leaves' surfaces. Though a relatively mild disease, repeated and untreated powdery mildew infections can greatly reduce the curly willow's vigour while causing growth stunt and premature defoliation. Powdery mildew is easily treated by pruning away the infected areas and applying timely applications of fungicide chemicals.
A detrimental willow disease, willow scab lies dormant throughout the winter months only to infect the curly willow during the early spring. This fungal disease infects the succulent young foliage of the willow tree, colonising just below the foliage's cuticle. The infected foliage wilts and defoliates from the tree while the uninfected foliage remains green and in place. While the disease may not spread through the curly willow's entire canopy in one season, continued and untreated willow scab infections will stunt the willow's vigour, causing dieback and stress. Most chemical treatments are ineffective for willow scab. The infected areas should be pruned from the tree, and all debris and defoliation around the tree's planting area should be removed and destroyed.
Tar spot is a harmless foliage disease that creates black, circular spots on the willow's leaves. The tar-like spots are pronounced with yellow outlines. Though unsightly, this fungal disease does not harm the curly willow's long-term health or cause stunt or dieback. Infected leaves that are dropped from the tree should be immediately removed and destroyed to prevent repeat infections. Chemical treatment is only effective when the entire tree can be saturated with chemical.