new foliage on avocado tree

Q. I have an avocado tree that has been on the property for almost 70 years. What is its life expectancy?
– Grace Hampton, Burbank
A. That is very old for an avocado tree. The original ‘Hass’ (rhymes with pass) avocado tree was planted in La Habra (Orange County) in 1926 and died in 2002, at the age of 76, of root rot. Avocado root rot, caused by a Phytophthora fungus, leads to the demise of most avocado trees.
I have not heard of an avocado tree, at least in Southern California, that lived longer than 76 years. The oldest avocado tree I know of in our area, which was bearing several hundred fruit as of last weekend, is located in the park in Franklin Canyon, at the end of the extension of Coldwater Canyon Boulevard, south of Mulholland Drive.
By the way, the original ‘Hass’ avocado tree was an accident. When it was a young seedling, Rudolph Hass tried to graft a green avocado variety, ‘Fuerte’, onto it, but the graft did not take. For three years, grafts were made without success. Finally, Hass decided to just leave the tree alone and it eventually produced the unique black and pebbly fruit that would bear his name. Every ‘Hass’ avocado tree in history has been propagated as a clone, albeit many generations removed, from that single tree. Here’s an interesting side note: Mr. Hass’ wife lived to the age of 98, an achievement that may have been due, in part, to her practice of consuming, at breakfast each morning, a half piece of wheat toast topped with avocado slices.
Q. I have a situation with my two avocado trees that I hope you can help me with. One is a ‘Hass’ that is looking sparse, with yellowing leaves. The fruit that set this year was about half the size as usual and, suddenly a few weeks ago, turned a reddish color and all dropped off. The other tree is a green variety, possibly a ‘Bacon’, and looks healthy, with plenty of dark green leaves. The fruit on that tree seems of normal size, and none has dropped. Both trees are about 5 years old.
– Wayne Boswell, Simi Valley
A. While premature fruit drop in avocado trees is normal, loss of all the fruit is not. I would attribute this to either too much or not enough water. Excess water can lead to root rot disease, whose symptoms include yellowing leaves and early fruit drop. By the same token, inadequate soil moisture can also result in fruit drop.
Up until now, our winter has been relatively dry. Avocado trees are water needy and, even in winter, will benefit from irrigation in the absence of rain. One practice that cuts down on both irrigation and the incidence of root rot is to allow fallen avocado leaves to accumulate on the soil beneath the tree. Your placing a ‘Bacon’ tree next to a ‘Hass’ is sensible. Although a single ‘Hass’ tree produces some fruit, its yield will increase several fold when planted next to a green variety such as ‘Bacon’ or ‘Fuerte’.
Q. After a remodel and new landscaping, my flower beds have developed nematodes. Nothing seems to thrive. Every new plant eventually rots or develops ‘blood balls’ on stems and roots. Flowering maple (Abutilon), Hebe, Salvia (‘Mystic Spires’ and other varieties), Shasta daisy, Gaura and Lantana have been affected. All efforts, save solarization, have not solved this problem.
– Phyllis Robinson, Woodland Hills
A. An occasional pest in the West San Fernando Valley, nematodes are microscopic, unsegmented, parasitic worms that produce obstructing knots or nodules in plant roots, impairing roots’ ability to take up water and minerals.
Nematodes tend to inhabit rich, sandy soil and are difficult, if not impossible, to eradicate once they have a foothold. One cultural control is to till the ground every 10 days during hot weather. This brings nematodes to the surface, where they die from desiccation.
There are two types of problematic nematodes: ectoparasites, which live outside of roots and, utilizing a piercing stylet, suck out root contents, and endoparasites, which live entirely inside plant roots. Only a minority of nematodes are pests. Most types feed on decaying plant matter and may serve as biological control agents that parasitize soil insects, such as fungus gnats, that pupate in the soil and would otherwise cause serious problems.
Soil solarization is the most reliable method for nematode control. In this procedure, tilled and moistened soil is covered with clear plastic during very hot weather for three to six weeks.
Other control techniques include mixing diatomaceous earth into the soil, introduction of beneficial nematodes that devour their pestiferous cousins and application of bacteria or fungi that infect and kill nematodes. Nematodes would seriously restrict orchard production in California were it not for the nematode-resistant rootstock known as Nemaguard.
About 85 percent of almond, peach, plum and nectarine trees in California are grafted with this rootstock. If you purchase one of these trees for your yard, make sure the rootstock is Nemaguard. When selecting tomato seeds, the packet must bear the initials VFN. The “N” in this acronym means that the seeds in the packet are resistant to nematodes. (The “V” and the “F” represent resistance to verticillium and fusarium fungus.)
Asparagus, corn, onions, garlic, ‘Cherokee’ red clover, and strawberries are resistant to nematodes, as are ‘Charleston Belle’ and ‘Carolina Wonder’ bell peppers, ‘Nemagreen’ lima beans and ‘Carolina Cayenne’ chili peppers. Marigold, Zinnia, Coreopsis, Ageratum, black eyed Susan (Rudbeckia) and the native blanket flower (Gaillardia) are unaffected by nematodes.
Tip of the week
Bob Ginn, grounds maintenance supervisor at the Hollywood Bowl, has enlightening information regarding the usefulness of dichondra, a creeping ground cover, with one inch, circular, fan-shaped leaves, that spreads by both above ground stolons (runners) and underground rhizomes.
“Many seemingly sane people spend hours of their time trying to grow a dichondra lawn. Not me. Although knowing the plant liked well-drained soil and high nitrogen, I was amazed to see how it grew like a weed in pure decomposed granite between the cobblestone rocks I’d placed around a bubbling bird pond we constructed. No sprinkler system – only hose watering and splash over from the pond. It looks nice with little maintenance and minimal watering.”