Getting to the Root of a Fungus Disease Infecting Many Gardens

Question: Oak root fungus is a big problem in the hills, and there is little one can do about it. Some say there are no plants that are 100% resistant to it. Do you know of any?

--C.A., Pasadena

Answer: Oak root fungus is a serious problem, but there is much one can do about it and there is a very good list of resistant plants. Harold Mitchell, of Mitchell Pest Control in San Gabriel, has been battling oak root fungus for 50 years and says that half of the dead trees he has “autopsied” have died of this fungus disease. It is very common in the foothill communities.

You can find descriptions of oak root fungus--also called armillaria root rot--in many books and articles, but they seldom mention that any perennial plant--not just trees and shrubs--can get the disease. It is not spread by spores, like most fungus diseases, but by root-like mycelium that fan out from the infected roots of other plants, which can be up to 30 feet away.

Over-irrigation favors oak root fungus, but infected plants can be saved. Mitchell proudly points out trees that are strong 50 years after he began treating them. “If there’s anything I want to be remembered for, it’s all those trees I’ve kept alive,” he said.

The University of California Division of Agricultural Sciences publishes a booklet called “Resistance or Susceptibility of Certain Plants to Armillaria Root Rot” (Leaflet 2591, $1.75 plus shipping; call [800] 994-8849 to order a copy).

You will find well over a hundred ornamental plants that are considered immune or highly resistant enough to easily make a garden even where oak root fungus is a serious problem

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Q: My lawn is suddenly full of slightly elevated burrowing trails. I think this might be the work of moles. Can I use one of those sound devices I see advertised on the Web to chase them away?

--J.S., Los Angeles

A: Despite advertising claims, all of the various sound devices “do absolutely nothing,” said Raymond Smith, the supervising agricultural inspector for the Los Angeles County agricultural commissioner’s office. The devices do not get rid of moles, gophers, rats, raccoons, deer or insects. It has been proven many times over that they do not work.

Smith points out that moles don’t eat plants. “If they were in my garden, I’d leave them alone,” he said. “Besides, there are virtually no controls that reliably work.”

Moles are not rodents, like gophers and rats, but are insectivores and have a voracious appetite for bugs, grubs and earthworms, which is what drew them to your lawn. The only damage they cause is cosmetic--those raised areas you referred to. They also make the occasional exit hole.

One way to tell a mole from a gopher is by the shape of the exit holes. Moles come straight out of the ground like the space shuttle lifting off, so their holes resemble miniature volcanoes, with the dirt evenly distributed.

Gophers, on the other hand, exit at a 45-degree angle, which makes a lopsided mound with most of the dirt to one side. “It’s easy to tell the two apart,” said Smith.

While gophers can be controlled by traps or special fumigating pellets (available only to professional pest-control people), the traps for moles are rather expensive and aren’t often successful. There are no poisons approved for use on moles.

“That’s the bad news,” said Smith. “The good news is that moles are not very common” in Southern California, unless, of course, “they happen to be in your yard--then it seems like there must be hundreds.”

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