Our normal scorching July temperatures are right on schedule and the effects of heat stress as well as drought stress on many trees are becoming obvious. Some summer branch death is normal in our arid, hot climate but this year tip, twig and branch dieback is severe, especially on badly pruned trees. Bad pruning techniques include topping or lopping off the top of main branches, lion's tail pruning which strips off all secondary branches leaving just a tuft of leaves at the end of a branch and thinning that cuts out more than one third of the branches or canopy. Bad pruning can stress trees so severely that they die, usually within seven years. The three year drought we're experiencing has sped up the degeneration process-main branches and heavy limbs are dying quickly and quickly becoming hazardous.
Major pruning during hot weather is never recommended; heavy pruning in the summer months removes the leaves that serve as the tree's food source and opens the canopy to sunlight that can burn the bark. But dead main branches and heavy limbs must be removed soon before they fall off.
Removing large dead branches is not a job for amateurs. Any tree that is over 15 feet tall is required to be pruned by a certified arborist and an expert arborist will be able to determine how best to remove dead limbs without compromising the balance and structure of the tree. It doesn't do much good to remove a hazardous dead limb only to have the entire tree fall over.
Homeowners or their gardeners can prune out dead wood on trees less than 15 feet tall. There are several important steps to follow. First make sure that the wood is really dead. Heat and drought can cause complete leaf drop. Take a sharp knife blade and lightly scrape the bark. If the layer just under the brown exterior bark is still green, the branch is still alive. Secondly, sharpen your pruning tools. Dull blades make ragged cuts and can tear away live bark beyond the intended cut location. Third, never leave a stump! As stumps die back, the rotting process can carry disease pathogens and bacteria into healthy tissue. Make all cuts at a branch or trunk junction. Pruning cuts should be made flush with what is called the branch collar, a raised ridge of tissue between a branch and the trunk or another main branch. It's called the collar because it looks just like a dog collar.
Pruning cuts made flush with the branch collar will naturally self seal. No need for pruning paint to seal the wound — the tissue at the collar site will release enzymes that create a natural sealant.
We can expect that severe branch dieback will continue until winter rains thoroughly soak the soil. If possible, deep irrigate large landscape trees with dying branches weekly until temperatures cool in the fall.