How to maintain the health of walnut trees

Q: My large walnut tree has many dead branches this year. Can it be saved? — Tom in Paso Robles

A. 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 that less than 20 percent of a tree’s branches are dead, you can prune them back until you get to the green living part. 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 spread of fungal diseases. You can mark the dead areas by attaching tape to them so that 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 a tree’s vigor. Check for small holes in branch and bark tissue to look for boring beetles.

If you need help identifying these or other pests, contact the Master Gardener Helpline in Templeton at 805-434-4105.

If you have determined that the age of the tree and the amount of dead branches warrants the tree’s removal, get the site ready now for planting a new tree next year. 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 plant 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.

Save the date!! The UCCE Master Gardeners’ Tomato Extravaganza will be held from 10 a.m. to 2 p.m., Aug. 29, at the Garden of the Seven Sisters, 2156 Sierra Way, San Luis Obispo. It will feature tomato and basil tastings, a plant sale, presentations, and more. Watch for the full article on Aug. 26!

This story was originally published August 19, 2015 at 4:55 AM with the headline "How to maintain the health of walnut trees."