Overwatering may be root of problems

Master gardeners from the University of Nevada Cooperative Extension have returned to the Molto Vegas farmers market on Thursdays to answer home-gardening questions.

The market is held from 11 a.m. to 1 p.m. every Thursday at 7485 Dean Martin Drive, Suite 106.

We will have native bee boxes available for pollinating your home orchard and vegetable gardens and various fruit woods available from the orchard in North Las Vegas for grilling.

The master gardener help line is always there to help gardeners in the valley by calling 257-5555.

Q: After four consultations, two tree doctors and months of consternation and heartbreak, I still have Italian cypresses dying with the little branches browning from the trunk out. They become brown with little green tips and eventually all the needles fall off. Then branches started fading to a pale green and dying perfectly in place.

As I have removed them, ugly gaps in the tree's beautiful form result. The bark has become rough and ugly and, in spots, has opened big gaping holes. Inside those holes is tan-colored, healthy looking tissue. There are splits in the rough bark with a fine stream of dried sap running down from them. Now it has jumped the sidewalk and spread to the very healthy tree. The big, full, healthy tree has a hole an inch in diameter in its smooth, otherwise healthy bark. Why did you say in your column to "hose them off a couple of times a year"? Can one wash them too much?

A: Let's run down some of the problems with Italian cypress. There aren't that many.

You hit upon one: spider mites. Mite damage does not have to have webbing to be mite damage. Some of these plant destructive mites do not spin webs. Generally, we have two different types of mites, one that spins webs and the other that does not.

Also, just because you see webs does not mean you have spider mites. There are harmless spiders that spin webs that can resemble spider mite webbing. Better indicators of mite damage than just webbing is the dusty appearance on the foliage from dead carcasses of mites and dust accumulation. But like you said, this does not sound like spider mites.

Dust accumulation helps plant-destructive mites by providing obstacles that impede their natural enemies, which are other mites. The mites that hunt down the spider mites are not damaging to plants. So, periodically it is a good idea to hose off mite-susceptible plants to wash away accumulated dirt and allow the predatory mites a chance to catch and kill these bad mites.

Of course washing off the foliage also helps other insects that hunt mites find them as well. Washing too often? Not really a problem. Just wash them when you see an accumulation of dust or after a dust storm.

Other problems include overwatering so that the roots stay too wet and rot. An early indicator of this may be the drooping of branches due to rapid, succulent growth in earlier years followed by individual branch dieback. These drooping branches are often used by birds for roosting, which makes the problem worse. This sounds much more like your problem than spider mites. If the soil does not drain well or the spot has a tendency to accumulate water, the trees may slowly die, one branch at a time.

The last problem, which others have reported but I have not seen, is borer damage. I have had people report Italian cypress dying, and these people claim borers but I still have not seen borers damaging Italian cypress. Arizona cypress? Yes, borers frequently damage Arizona cypress but I have not see it in Italian cypress.

There are insects, such as carpenter bees, that will attack dead wood and make large holes like you describe. Carpenter bees tunnel into wood to lay their eggs and leave very large holes about the size you mention. Bare, unpainted or weathered softwoods are preferred, especially redwood, cedar, cypress and pine. I will include a picture of carpenter bee damage to a palm in my newsletter.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.