Walnut Tree M.D.
By Jutta Thoerner UCCE Master Gardener
My large walnut tree has many dead branches this year, can it be saved? Tom in Paso Robles.
If you drive by the walnut and almond orchards in Paso Robles, many dry farmed for centuries, you will notice the same problem. The last four years of drought have left their mark by killing branches in the canopy. This “die back” is generally not reversible, especially if the trees are older. Walnut trees will near the end of their productive life after 40 years. If you see less than 20 % die back, you can prune back the dead branches until you get to the green living part of the tree. This should result in new branch growth the following spring. Most arborists advise you to prune during the dryer months of the year to prevent the spreading of fungal diseases. You can mark the dead areas by attaching some tape to it so you can distinguish the dead from the live wood once all the leaves have dropped.
Monitor the health of your trees by checking for insects; walnut husk fly and codling moths will deposit their eggs in the nut meat, scales and mites will affect the vigor of the tree. Check for small holes in branch and bark tissue to monitor for the presence of boring beetles. Contact the Master Gardener Helpline for assistance with the identifying any of these or other pests.
If you have determined that the age of the tree and the amount of die back warrants the removal of the tree, get the site ready now for next year's replant. If a total tree and root removal is not an option, cut the tree now and leave the stump to dry out for the rest of the year. You can replant a new tree in January or February when bare root trees become available. Most walnut trees in the nursery are already grafted and many new varietals are now available. Since walnuts are wind pollinated, planting just one tree is an option if there are other walnut trees in your neighborhood.