Mesquite trees are one of the toughest trees that grow in the desert and are usually problem free. The root system of a mesquite has been known to extend 200 feet below ground and horizontally far beyond the plant canopy. They are hard to kill, and their perseverance has to be admired. However, occasionally mesquites do develop problems.
Mesquite Twig Girdler
The mesquite twig girdler is also known as "nature's pruner" since it attacks mesquites and other desert trees and non-selectively girdles branches causing them to die and fall off. While this is unattractive, there is little you can do to prevent it. The insect that causes the damage is a beetle about ½ inch long with antennas almost as long as the body. They chew a spot on the branch and lay eggs just inside the bark. When the larvae hatch they chew all the way around, girdling and killing the branch. Controlling this insect with pesticides is not warranted since when the damage appears the beetle is long gone. Although annoying and unsightly, the damage to the tree is minor.
The desert form of mistletoe affects most trees in the desert, especially the mesquite. Birds transport mistletoe seeds from tree to tree, infecting the branch through droppings. Mistletoe also travels through the root system from tree to tree.
Once a tree is infected with mistletoe, it is impossible to eradicate. Mistletoe is a parasite that eventually kills the host. However, it does take many years for the mesquite to die, and you can extend its life a very long time by cutting mistletoe out of the tree every time you see some sprouting from a branch. Cut the branch all the way back to the point of origin.
Slime Flux Disease
This disease appears on mesquites as sap bleeding accompanying wilting and dying of branches. The fluid that seeps out of the wound is dark and smells bad. There is no cure if your mesquite has this disease, and the only thing you can do is provide preventative care. Make sure your tree is watered during the hottest and driest part of the summer to prevent drought stress. You can prune out an infected limb, but this will not stop the disease from killing the tree. This disease should not be confused with the propensity that mesquite trees have for bleeding sap when large limbs are pruned. This is natural and normal. There is no odor associated with this kind of seepage.
Mesquites can survive on very little water, so little that normal desert rainfall is enough for trees in the desert to survive just fine. However, if you want your tree to grow faster and have lush foliage, giving it extra water is a good idea, especially during prolonged drought or during the hot, dry months of summer. Soaking the entire area underneath the canopy, not at the base of the tree, at least 5 feet down, will perk up your tree, and you will see a significant growth response within a growing season.