Does your tree look like it has a disease? It is common for Mistletoe to invade a host tree and become a parasite. Desert mistletoe is a true evergreen plant and is an obligate (binding) parasite on its host.
Mistletoe is one of the main causes of diseases in mesquite trees and is native to much of the eastern third of the U. S. Mistletoe plant berries are said to be poisonous, but birds do eat them.
Desert Mistletoe or mesquite mistletoe, Phoradendron californicum, is a parasitic plant native to southern California, Nevada, Arizona, and Baja California. It can be found in the Mojave and Sonoran Deserts under 4000 feet elevation. The female Mistletoe plant produces red seeds that the birds love to eat.
Mistletoe seed and red berries are an important part of the desert bird’s diet. The seeds are “sticky” and birds bring them to branches of trees where they perch. The seeds germinate and grow inside the tree. The species most affected are the leguminous trees in the low desert including:
- mesquite, Prosopis
- palo verde, Cercidium
- ironwood, Olneya
- acacia, Acacia greggii
The mistletoe seeds germinate and grow into the tree with sinkers (organs acting much like the roots of a plant). The mistletoe sinkers absorb water and nutrients from the tree host. These mistletoe roots grow inside the tree for some time eventually producing the conspicuous growth of stems, leaves and bulges.
Mistletoe takes a long time to kill a tree but certainly causes decline. Mistletoe infections cause swelling and witches’ brooms (what is called the growth of stems seen in the photo below). Old severe infections may result in swollen areas of dead wood that are brittle and break easily. These limbs should be removed if they pose any danger.
The only way to control mistletoe is to remove it manually. Put some gloves on and remove the mistletoe growth and stems with your hands. Manual removal does not kill the mistletoe because it is growing inside the trees tissue; but good control can be achieved by removing it.
Pruning out heavily infected branches may help… but that decision is usually based on how much can be pruned without destroying the beauty of the tree. Also, it is impossible to know if you have pruned far enough away from the infection to get all the mistletoe that is growing inside the host.
Wrapping pruned sites is not recommended since such procedures do not kill the mistletoe and may easily cause more harm than good to the tree. Sprays sold for mistletoe control will remove the outside growth just as pruning, but they do not kill the part of the mistletoe plant inside the tree.