Help for the Home Gardener from the Contra Costa Master Gardener Help Desk
Client's Problem and Questions:
Photo: Craig Lee/The Chronicle
Until about three years ago, our Gravenstein apple tree located in our garden in Martinez was a healthy 35+ year old tree producing an ample crop of apples. Then it began to decline. First, twigs wilted, then dropped off; then, branches, and last summer complete limbs. A "mystery" apple tree nearby, probably about the same age, has shown no signs of distress.
While this was going on, the tree was still producing apples but could not carry them until they were ripe – they dropped off. In early September, we finally cut down what was left of the tree, one slim branch that had developed atou 4 years ago and was still hanging on with foliage, flowering in spring, but had lost its few apples.
What we found was that the trunk started to hollow out about 3 ft above soil level. When we dug around the bottom to get at the roots we discovered that all the very substantial roots were spongy, slightly damp, and smelled moldy, except for one very small part of one root that must have kept the remaining branch alive.
The bottom of the stump is filled with little rootlets. The big roots were so deteriorated that the stump could be pulled out with little force.
1) What caused the tree to die?
2) Whatever it is, can it affect the trees around it, including another adjacent apple tree?
3) Can another tree be planted in its place? Any kind?
CCMG Help Desk's Response:
I am writing this with what I believe you will find to be relatively good news about your deceased gravenstein apple tree. I did have an opportunity to show the debris samples that you brought into our Help Desk office to a plant pathologist. We looked at the samples and discussed the information that you had provided about the decline of the tree and what you had found while you were removing the tree.
The pathologist found no evidence in the samples you had provided that the tree was killed by a pathogen. She concluded that the apple tree may well have just reached the end of its life expectancy. There were signs of fungal growth in the samples (includingTrametes versicolor, commonly known as turkey tail wood rot), but the pathologist said that they were the kinds of fungi that attack wood that is already dead or badly stressed. The presence of the turkey tail fungus could have been the cause of the white spongy areas you reported that you observed while removing the tree. The types of fungi that were present in the sample you brought in should not be harmful to other healthy trees or other plants in your garden. For more information on such “wood decay” fungi, see http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74109.html. You can find a photo and information about turkey tail wood rot near the end of the Pest Note.
The pathologist also found no evidence in the samples that the tree had been killed by a root rot problem such as phythopthera (http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/DISEASE/pchphytoph.html) or armillaria (http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/DISEASE/oakrootfungus.html), both of which, if present, could spread and kill other trees and vegetation.
You indicated that the tree was more than 35 years old. Since I am aware that apple trees can live much longer than that, I did some research to find out what the typical expected life span of an apple tree might be. While I didn't find any information specific to California about life expectancy of apple trees, I did find reputable sources in Arizona and in Virginia that each indicate that the life expectancy of a standard size apple tree is 35 to 45 years (and less for dwarf and semi-dwarf trees): http://ag.arizona.edu/pubs/garden/mg/fruit/intro.html and https://pubs.ext.vt.edu/426/426-841/426-841_pdf.pdf. Given that the life expectancy answer was the same in these two very different climate and growing zones, it seems reasonable to generalize it and apply it more broadly to California trees. Thus, it does seem quite possible that the gravenstein apple simply declined and died at the end of its natural life expectancy.
If the adjacent “mystery” apple that you reported liking so much is the same age as the gravenstein, you might want to try grafting scions from it onto a younger tree next spring. If you need assistance with the grafting, you might contact the California Rare Fruit Growers to see if they can recommend classes or someone who could help you. Here's a link to the website for the CRFG's Golden Gate Chapter: http://crfg.org/chapters/golden_gate/index.htm. The group has monthly meetings that are open to the public. They also hold a scion exchange each year—in 2014 it took place in January in Berkeley. You can find information about the meetings and the scion exchange on the same website.
I hope that the mystery apple continues to thrive—both in its current form and perhaps on a younger reincarnation. Maybe you can also find an equally good variety to replace the Gravenstein.
Contra Costa Master Gardeners Help Desk
Editor's Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523.
We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/