What Are Black Spots on the Fronds of Queen Palm Trees?

Diamond Scale

• The Queen palm (Syagrus romanzoffiana) is susceptible to attack from Diamond scale, a fungal disease caused by the pathogen Phaeochoropsis neowashingtoniae. Its common name is derived from the diamond-shaped fruiting bodies that form on the fronds, or leaves, of the tree. The disease causes the development of tiny, black, water-logged spots that grow in size to approximately 3/10 of an inch in length and can be found on both the upper and lower surfaces of the fronds.

Damage

• Older leaves on the Queen palm are lower on the tree and suffer the most infection from Diamond scale. The fronds will develop a covering of black, sooty powder that falls easily from the leaves. Those fronds eventually turn yellow and brown, then die from the disease and leave large sections of the tree barren of foliage. The disease typically does not kill the entire tree, but the stress from the infection will reduce the vigor of the Queen palm and leave it susceptible to other serious diseases.

Leaf Spots

• All species of palm trees are subject to leaf blight and leaf spot diseases caused by a number of different fungal pathogens. Symptoms are similar regardless of the specific fungus and initially display as tiny, water-logged lesions that take on a number of colors including black, brown, gray, reddish-brown and yellow. The lesion is typically surrounded by a circle of tissue that bears a color different than the spot itself. The diseased tissue will eventually die.

Leaf Spot Management

• As the leaf spot of a Queen palm progresses, entire fronds may fall to the ground. Young palms are the most frequently affected and the presence of these fungal pathogens can be minimized by ensuring that the Queen palm enjoys good air circulation to allow for quick drying of the leaves. Keeping the fronds as dry as possible will discourage the development of leaf spot and leaf blight. Prompt removal and destruction of all diseased litter prevents the further spread of the fungi to other fronds and plants.