Many species of fungi and bacteria seek opportunities to reproduce through palm trees, often damaging or killing the trees in the process. Generally bacterial diseases are more severe and often they cause tree death. Fungal diseases do not usually require chemical treatment and can be prevented easily by application of fungicide. There are several diseases that are particularly prevalent among palms in Texas, and it is important to identify these in infected trees so that the diseases can be controlled.
Texas Phoenix Palm Decline
This disease is also known as Date Palm Lethal Decline, although it affects other types besides date palms. It is caused by a phytoplasma, a bacterium without a cell wall. It starts by attacking the roots of the palm and quickly spreads upwards, causing leaf death. It is ultimately fatal. This disease is especially prevalent in south Texas, and is severe enough that certain counties have palm quarantines in place.
Lethal Yellowing Disease
This disease is also caused by bacteria. Leaves will yellow and wilt, starting with the lowest foliage and progressing upwards. Eventually it will cause all the leaves to die and leave the trunk bare. There is no cure for the disease, but injecting the tree with antibiotics will control the symptoms. Several species are resistant to this disease, including the Mexican and California fan palms and the pygmy date palm.
Leafspot is usually caused by a variety of fungus species, and manifests as small brown or black spots on older leaves. It can also be caused by potassium deficiency and even by fungicides. Even when leafspot is caused by fungi, chemical control is usually not needed. The disease is usually a sign of some kind of stress that the tree is undergoing, such as insufficient drainage.
This disease manifests as small black spots on both sides of the palm leaf. The spots can be distinguished from those caused by leafspot in that they are wart-like and often have yellow filaments extending from their centers. It is common in south Texas. The disease can cause leaf death if it is severe enough. Copper-based fungicides will prevent false smut from occurring, but chemical control is rarely required.
Rachis Blight is also caused by fungi. The first symptom of the disease is browning of the leaves along the rachis (or main axis of the leaf). Eventually fruiting bodies will begin to grow and the surface of the leaf will be broken, releasing masses of spores. There is, unfortunately, no effective treatment of this disease. Cutting and disposing of infected leaves may help prevent its spread.