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YOLO COUNTY NEWS
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We get questions! Late-summer odds and ends

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From page A8 | August 30, 2012 | Leave Comment

Sudden death of trees.

Littleleaf linden (Tilia cordata) and a 20-year-old lemon are recent examples. A dying 120-year-old camphor tree in downtown Sacramento was recently in the news as well.

It is very sad and perplexing when this happens. In the case of the linden, we deduced that it succumbed to Verticillium wilt. That was also the reason given for the decline and removal of the camphor tree. The lemon probably was killed by Phytophthora, also called crown rot.

There is no preventive for Verticillium. The fungus invades the water-conducting tissue of the tree (the xylem) and blocks the ability to take water up to the leaves. Growth is stunted, the canopy thins out badly, and the tree gradually dies. It occurs particularly where tomatoes were a crop before houses were built. In selecting a replacement, consider trees that are listed as resistant.

Phytophthora, on the other hand, attacks plants due to changes in the environment. Ubiquitous in our soil, it attacks a plant that has been made vulnerable by something we have done around it. Most common is an increase in frequency of watering, or addition of mulch around the trunk of the tree. Crown rot needs warmth and moisture to infect the trunk. Sometimes a tree can be saved by pulling away the mulch or lawn or ground cover, and changing the watering to much deeper applications on a less frequent schedule.

Crown rot is the most common cause of death of native plants in the landscape, and is a common problem on other drought-tolerant non-natives such as lavender and rosemary. Water more thoroughly and less often to avoid Phytophthora, and keep mulch pulled away from the stem or trunk.

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Sticky drip under my Chinese hackberry tree!

Return of the Asian woolly hackberry aphid! What can be done this late in the season?

The same pesticide (imidacloprid) that has been used since this pest showed up in 2002 is still the recommended treatment. It can be applied at any time of year, as it remains in the plant for a full season. It takes a month or so to get up into a big tree.

The resurgence in this pest may be due to homeowners gradually cutting back on the treatment. Or two mild summers back to back may have enhanced the aphids’ reproductive rates. Note that the aphid doesn’t really weaken the tree. It is “just” a nuisance as the tree drips honeydew all over your yard.

This is one of the few cases where I still recommend this systemic insecticide, as it is justifiably controversial. If you don’t want to use a pesticide, invest in a pressure washer. The material coating your yard is basically sugar solution, and rinses off.

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So many questions about shade gardening!

“I’m looking for shrubs for shade.”

“What do you have for color for shade?”

“I’m looking for plants for shade. I was looking at the Arboretum All-Stars list, but they aren’t sorted for shade or sun.”

We love our shade trees, but they do create landscape challenges, as there are fewer choices. It is easier to find shade plants with interesting leaf color and texture than flowers.

Key questions:

* What causes the shade? Is it year-round, or is there sunlight when trees drop their leaves? Some plants can take a winter-only sunlight cycle, such as spring-flowering bulbs.

* How deep is the shade? Bright shade is easy. Far fewer plants tolerate deep shade.

* How is the area watered? Lots of shade plants originate in high-rainfall climates. Dry shade is more challenging, but not without choices.

The Arboretum All-Stars list can be a great starting point in looking for adaptable plants for particular situations. To search by various criteria, go to the All-Stars Plant Search (http://arboretum.ucdavis.edu/plant_search.aspx).

Some of my favorite low-maintenance shade plants from their list include:
* Chain fern (Woodwardia fimbriata) and Holly fern (Cyrtomium falcatum), both of which are reasonably drought-tolerant for ferns.

* Easy shrubs include the native Mahonia and Ribes species; and

* Showy vines such as Chilean jasmine (Mandevilla laxa) and Australian bluebell creeper (Sollya heterophylla).

We also have articles about shade gardening at our website (http://redwoodbarn.com), and I have experience with shade gardening, since I live with a massive old sycamore tree at the very front of my house.

The star of my shade garden at the moment is Abutilon, sometimes called flowering maple, but it’s actually in the mallow family. It blossoms spring through fall with bright hibiscus-like flowers that attract hummingbirds. In the winter I love the fragrance of sweet box (Sarcococca ruscifolia) and the blooms of Lenten rose (Helleborus orientalis). Coral bells and alum root (Heuchera hybrids) give interesting foliage year-around. Many of these have brightly colored leaves; spring blooms are a bonus. Turf lily (Liriope) is tough, reliable, and has pretty purple summertime flowers.

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What is the easiest houseplant? I kill, like, all my houseplants.

Our annual back-to-college question. Two choices for “easiest”: easy ZZ plant (Zamioculcas zamiifolia), an upright grower, and golden pothos (Epipremnum aureum) which is a climbing or trailing vine. In general, members of the philodendron family, such as these, are your best bet.

Most people kill houseplants by watering them too often, and trying to grow them in too little light.

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I keep buying Venus flytraps, and they keep dying.

Quick summary of “how to grow ‘em” principles:

* Grow them in sphagnum moss;

* Give them the brightest light possible;

* Use bottled or pure water;

* Provide even moisture; don’t let them dry out;

* Don’t fertilize them;

* Remember they go dormant in winter; and

* Stop poking them! The thigmotropic response in each leaf occurs only a few times.

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Citrus tree in my lawn seems to be growing OK, but the leaves are always yellow.

Leaf samples showed classic iron chlorosis, sometimes called interveinal chlorosis. But other leaves were just generally yellow, indicating a lack of nitrogen.

Citrus trees, like other fruit trees, are best watered as in an orchard, not like a lawn. Shallow, frequent watering leads to loss of nitrogen from the soil, and our hard water makes micronutrients such as iron less available. Deficiencies that cause yellow leaves are common, so you have to fertilize more often. And there is a risk of Phytophthora crown rot (see above). Water deeply every couple of weeks to allow the surface to dry between waterings.

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What are those weird things on oak leaves? And those little hopping things under oak trees?

Those are galls, caused by tiny (non-stinging) wasps. While they occur on many different plants, the majority of species that make galls occur on oaks.

About galls:

The life cycle in general is as follows: The female deposits (oviposits) her egg in the leaf or stem. The larvae hatch and begin to feed. The plant responds by growing cells very rapidly, a tumor-like proliferation that surrounds the larvae. Possibly there are secretions in the mouthparts of the larvae that contain plant hormones, or some other chemical triggers the rapid cell growth. The leaf or stem tissue surrounds the larvae, which then develop inside the plant. After they pupate, the adult wasps emerge by chewing a hole in the gall.

Some galls form specific shapes in response to a pattern of feeding by the wasp larvae. Some galls attach securely to the leaf. Others fall off: The amazing jumping gall (unique to the Sacramento Valley) is a tiny gall that falls to the ground and “hops” while the larvae are still active.

It is not a symbiotic relationship. The tree gains nothing from the gall-forming wasp. There is some loss of chlorophyll at the site of some galls, but other than that the tree isn’t harmed or weakened.

A great reference site for information and pictures about this topic and other aspects of biology is run by Wayne P. Armstrong of Palomar College. Check it out at http://waynesword.palomar.edu/pljuly99.htm.

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I was in a big store and saw some princess flower. What beautiful purple flowers! Do they do well here?

Caveat emptor? Or “forewarned is forearmed”? Tibouchina urvilleana is unlikely to survive our winters, even with protection.
A lot of tender plants are sold in chain stores in Northern California. Some might live here, some won’t. Most of those stores stock similar products throughout the state, regardless of regional climate differences. I strongly suggest reading the label carefully. Look for the minimum temperature. Then ask locally.

Not all subtropicals are equally tender. Examples: Lantana is killed back, often to the ground, but always resprouts. Bougainvilleas can survive a winter if planted in a warm microclimate, and usually will recover sufficiently each summer to give abundant growth and bloom. Chinese hibiscus rarely survives. And unfortunately, that is also the case with princess flower.

Want a purple flower? Try purple potato vine (Lycianthes rantonnetii).

— Questions for future columns? Send them to redwoodbarn@gmail.com

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