• Spanish bayonet is susceptible to a number of fungal diseases.yucca image by photlook from Fotolia.com
  
  Native to the West Indies, southern United States and Mexico, aloe yucca or Spanish bayonet (Yucca aloifolia) is a tree-like shrub with 2-foot long spear-like leaves and white flowers on a spike that bloom every spring. Grow this dry-land coastal plant in USDA hardiness zones through 11 to add rough texture to the surrounding landscape. Although a hardy plant for the most plant, it is susceptible to a number of fungal diseases that affect its health.
  
  

Grey Leaf Spot

• Although not as common today as it was when it was discovered 20 years ago, grey leaf spot (Cytospornia) is a fungal disease caused by the pathogen Cytospornia sp. Symptoms include grey spots or lesions on foliage edges or tips that have a brown margin, with concentric circles of dark and light colors occur within. The disease manifests the leaf tips before spreading towards the leaf blade and killing it. Tiny black fruiting bodies exist on the grey part of the lesions that are visible to the naked eye.
  
  Grey spots are larger than brown spots, with some measuring up to 3 inches in diameter. Prune and discard older infected leaves to control this disease, and avoid watering the plant from above. Apply a fungicide containing mancozeb, chlorothalonil and zineb every week.
  
  

Brown Leaf Spot

• Brown leaf spot or Coniothyrium is caused by the pathogen Coniothyrium concentricum. Infected leaves feature oval-shaped, brown lesions that appear slightly depressed on the surface. Older spots are black with concentric rings of dark and light in between, while newer spots are lighter in color but have a dark center. In some cases several spots unite together to form a large lesion that varies in shape and size.
  
  Brown leaf spot appears on the upper side of the infected leaf first. Black fruiting bodies that are visible to the naked eye after four months appear in the sunken centers of the lesions. Control methods for both grey and brow leaf spots are the same.
  
  

Fusarium Rot

• One of the most common diseases on rooted cuttings is the Fusarium stem rot, caused by the pathogen Fusarium spp. that destroys the ends of soft stems first before attacking the leaves of the infected Spanish bayonet. Two types of fruiting bodies occur on the infected tissues---powdery clusters called conidia, and perithecia that are deep red and easy to identify with the naked eye.
  
  Control of this disease is achieved by using new and sterilized pots and potting medium, and good-quality, pathogen-free cuttings. There are no fungicides for this disease, so precaution is the only means of control.