Wednesday, August 27, 2008

PLASTICS MAY REPLACE CHEMICALS AS PLANT GROWTH REGULATORS

Red Gum Lerp Psyllid Update

According to University of California Entomologist Donald Dahlsten, the natural enemy introduced into California to control the eucalyptus red gum lerp psyllid is now established in eight California counties: San Mateo, Alameda, Los Angeles, San Diego, Santa Clara, Ventura, Monterey, and Orange. Dahlsten advises people to be patient, as a successful biological control program to control the lerp psyllid is likely to take some time. Dahlsten is in charge of the program that is rearing and releasing the parasites (tiny wasps) in various locations throughout the state. If the parasitoids are like others released over the years to control various pests, they will spread on their own throughout the remainder of the infested areas.

Some Plants May Be Pruned Now, Others Later

We can’t let winter go by without a discussion of pruning. For many people, winter and pruning go hand in hand, but the best time to prune really depends upon the kind of plant and the desired results. You can do light pruning anytime on most trees and shrubs. Regardless of the time of year, removing unwanted growth while it is small is easier and will have a less dwarfing effect on the plant than if removed later. Pruning out broken, dead, weak or heavily shaded branches also will have little or no dwarfing effect on the tree no matter when they are removed.

Evergreen trees and shrubs will be set back the least if you prune them just before spring growth begins. Most evergreen plants make their most rapid growth after the weather warms later in the season. Pruning these plants just before the period of most rapid growth keeps the most leaves productive for the longest time. Also, the pruning cuts will be quickly concealed by new growth.

If your plants are growing in a limited space and you want to hold them back, prune when growth is about complete. For many plants, the time to prune for maximum dwarfing is usually in late spring to mid summer. For example, many gardeners maintain fruit trees in small areas with summer pruning. Pruning during this period reduces leaf area for the longest period of time. However, pruning should not be so severe nor so early as to encourage new shoot growth. If you spring prune ornamental evergreen shrubs and trees, especially in highly visible spots in your landscape, try to make the cuts so they are not easily seen.

You can effectively direct the growth of young trees of all kinds of young trees during the spring and summer growing season. Encourage branches in desirable positions by pinching back or thinning the foliage of competing branches, or by entirely removing the competing branches that are in less desirable positions.

Corrective pruning can be done at any time, from winter through summer. However some problems are best corrected during the growing season when they are obvious. For instance, branches on fruit trees that are too low because of the weight of the fruit should be partially or completely thinned at the time the fruit is present. Dead or weak limbs should be removed in winter, but often they are easier to identify and remove in summer.

The correct time to prune flowering trees depends upon the flowering habit of the tree. Plants which bloom on current season’s growth, such as the crape myrtle, should be pruned during winter, before spring growth begins. Moderate to severe pruning will favor larger blossom clusters. Plants which flower in spring from buds on one-year old shoots, especially the flowering fruit trees, should be pruned at or near the end of the bloom period. That way you can enjoy the blossoms, then prune to encourage vigorous growth for next year’s bloom.

Pruning wounds sometimes exude plant fluids or “bleed” profusely on such trees as elm, maple, mulberry and oak. You can minimize such bleeding by keeping the cuts small (less than three inches in diameter and pruning in fall or early winter. The problem is more likely if pruning is done just before growth begins in spring. Bleeding is usually not harmful to the tree, but if it is heavy and persistent, it may cause bark injury below the pruning cut.

Young Trees, Like Children, Need Careful Training

While we’re on the topic of pruning, here are some thoughts to keep in mind as you train newly planted trees: 1) no more pruning should take place in a single year than is needed to enhance the shape or structural strength of the tree; 2) training can take place progressively over the next three to five years.

Unless the tree has a natural multi-stemmed habit, most landscape trees should be trained to a single dominant or “central” leader. The central leader is the topmost vertical stem extending from the trunk. Prune back competing lateral branches that threaten to grow taller than the leader. Double or “codominant leaders,” if left unattended, can pose serious structural problems for trees as they age. One of the two stems (usually the weaker stem) should be removed to establish the central leader.

During the years when you are training your young tree, you will also need to identify those primary limbs (scaffold limbs) that will eventually make up the tree’s framework. The height to the lowest scaffold limb will be determined partly by the anticipated activities that will occur under or near the tree. For example, if the tree is near a sidewalk, the lowest permanent limb will need to be at least eight feet high on the trunk to allow for clearance. For some small young trees, there may not be any permanent lateral limbs present for a year or two.

While you are waiting for the tree to grow and develop, it is very important to leave small temporary limbs on the tree at lower heights than eventually will be desired. Remember, these small limbs have leaves, and leaves are essential for nourishing the young tree.

When you finally begin to select permanent lateral limbs, select those that are spaced evenly and are distributed radially around the trunk and central leader. For trees that are expected to have a trunk diameter of 12 inches or greater at maturity, permanent lateral limbs should be spaced at least 18 inches apart along the trunk. Trees such as ash frequently have major branches occurring in pairs across the main stem. Pruning these alternately up to a height of 12 to 18 feet will create a structurally sound tree that is attractive and balanced. Never let one limb grow directly over a lower one.

You should give every tree you plant a level of care that will enable them to become established, then prosper for many years to come. Training trees when they are young will help ensure good growth and long term structural stability.

Moss and Algae Do Well In Wet Weather And Poorly Drained Soils

Our wet weather this winter has created ideal conditions for the growth of moss and algae in lawns, and I’ve received several requests for information on how to control the problem. When moss or algae invade a lawn, they weaken the grass plants by forming barriers to air and water movement into the soil,.

Mosses and algae are both primitive, nonflowering and rootless plants that form mats on the soil surface, preventing water and air from reaching grass roots. Mosses and algae are not plant parasites, and do not attack and harm grass directly.

Moss and algae require specific soil and climatic conditions to develop; they are favored by soil compaction and poor drainage, too much water, and a thick thatch layer. Also, moss is favored by low soil fertility, acidic soil conditions and heavy shade. Unlike moss, algae is favored by high soil fertility.

The best way to control moss and algae in turfgrass is to eliminate the causes of their growth while keeping the grass growing vigorously. Some of the things you can do include the following:

· Fertilize the lawn, if moss is the problem, or withhold fertilizer, if algae is the

problem.

· Aerate or core the lawn to reduce compaction and improve water penetration.

· Improve soil drainage by installing drain tiles or dry wells.

· Reduce the amount of water you apply.

· Remove excess thatch.

· If moss is present, reduce shade by selective pruning of trees and shrubs.

Where moss and algae are thick, you may want to apply certain chemicals for complete control. Spray applications of copper sulfate, ferrous sulfate or ferrous ammonium sulfate at the rate of 2 or 3 ounces dissolved in 4 gallons of water per 1,000 square feet works well. You may need to repeat the application if the infestation is severe. Copper sulfate may temporarily damage the grass, so use it only on very severe moss or algae infestations. Keep in mind that chemical treatments provide only temporary control, and that long term control depends upon eliminating the cause of the problem.

Nematodes and Woody Landscape Plants

Landscape gardeners sometimes encounter root knot nematode infestations in annual flower beds. Root knot nematodes usually cause distinctive swellings, called galls, on the roots of affected plants, making it fairly easy to identify an infestation. Because trees and shrubs may be growing in the same location, I’m sometimes asked what tree and shrub species are known to be susceptible to nematode injury. The following woody landscape plant species are known or suspected of being damaged by root knot nematodes in California: albezia, alder, boxwood, cactus, catalpa, cedar, euonymus, gingko, hibiscus, hydrangea, juniper, mulberry, oak, palm, pittosporum, rose and tamarisk.

While annual plants may be killed by nematodes, woody plants are rarely killed. Nematode injury to woody plants is usually less obvious and often more difficult to diagnose. Woody landscape plants that are heavily infested may have reduced growth and branch tip dieback and may defoliate earlier than normal. You can confirm a nematode infestation by collecting soil and root samples and sending the material to a laboratory for positive identification of the nematodes.

(Source: Nematodes. UC IPM Pest Note No. 7489. Univ. of Calif. Div. of Agric. and Natural Resources)

Coast Redwood Tree Problems

As well as coast redwoods (Sequoia sempervirons) seem to do in the Valley, I’m often asked to diagnose redwoods that have developed dead branches and seem to be dying. The calls for help are as common in winter as in summer. It’s important to understand that while coast redwood trees are susceptible to some serious diseases, they are most often injured or killed by abiotic (non parasitic) problems. They tend to grow poorly in heavy soils that are too wet, or in dry, compacted soils with poor drainage. High levels of soluble salts such as boron or sodium will stunt their growth and cause their leaves to turn yellow and “burn.” Coast redwoods are also susceptible to iron deficiency, especially in soils that have a high pH. They may be injured by freezing temperatures, especially in dry soil. Likewise, they will develop brown and scorched leaves during our hot and dry summers, especially if they’re not adequately watered. Drought stressed trees may then be attacked by bark beetles.

In dry or compacted soils the trees will grow slowly, and their trunks develop a distinct taper. Under ideal soil and moisture conditions, the trunks will be nearly the same diameter from the base of the tree to several feet high. Some brown foliage in the interior of the tree is normal. In fact, it is normal for the oldest leaves to turn yellow, then brown, and finally drop from the tree in late summer and early fall. It is also normal for short twigs to turn brown and fall. New growth at the ends of branches indicates that the branches are alive and healthy, despite some dieback of twigs and leaves.

As mentioned, coast redwoods are susceptible to some diseases. In the Stanislaus County area I’ve identified redwoods infected by Botryosphaeria canker (Botryosphaeria dothidea), crown rot (Phytophthora sp.) and Armellaria root rot (Armillaria mellea). However, these diseases are relatively uncommon on redwoods here. If you’re trying to diagnose a redwood problem, be sure to consider soil and water-related problems first.

Plastics May Help Replace Chemicals as Plant Growth Regulators

To help commercial nurseries keep plants uniform in size, University of Florida researchers are testing colored plastic films that filter out growth-promoting light waves. Sandy Wilson, an assistant professor of environmental horticulture with UF's Institute of Food and Agricultural Sciences, said the photo-selective plastic green film in her current experiment filters out far-red light, which is responsible for stem elongation in plants. Wilson’s goal is to inhibit stem elongation in annuals and perennials without sacrificing plant quality.

The horticulture industry prefers uniform plant size because it speeds plant establishment in the field and makes it easier to pack and ship mature plants. Chemicals are currently used to control plant height, but because of increasing environmental concerns, researchers are trying to find other methods to control plant height.

According to Wilson, most plants grown under the far-red light absorbing green film are about 25 percent shorter than plants grown under clear film, which is used as a control standard to compare effects of the colored film. The results are comparable to plants treated with chemical growth regulators.

One of the problems encountered so far has been a short film life. The dyes start to degrade after one year, so research is being conducted to increase the stability of the dyes. Another problem is delayed flowering time for certain species. Wilson says that growers may need to group plants in the greenhouse according to their light requirements, because photo-selective film has different effects on certain species.

Free Publications Recently Posted to the Online Catalog

These publications can be accessed for free as an HTML web page or as a downloadable PDF

document from http://anrcatalog.ucdavis.edu.

7490 Clovers: Pest Notes for Home and Garden

7491 Dallisgrass: Pest Notes for Home and Garden

7492 Glassy-Winged Sharpshooter: Pest Notes for Home and Garden

7493 Powdery Mildew on Ornamentals: Pest Notes for Home and Garden

7494 Powdery Mildew on Fruits and Berries: Pest Notes for Home and Garden

7495 Windscorpion: Pest Notes for Home and Garden

8040 Alternaria Diseases

8041 Damping Off Diseases

8042 Sclerotinia Diseases

8043 Biotechnology Provides New Tools for Plant Breeding

8046 Planting Landscape Trees

Recently Revised Pest Notes

7403 Elm Leaf Beetle

Upcoming Meetings:

Landscaping With Nature - Workshops for Professionals and Homeowners

Date: Wednesday, February 20, 2002

Time: Main Session - 8:00 a.m. to 4:00 p.m.; evening homeowner session - 6:30 to 9:00 p.m.

Place: Stanislaus County Agricultural Center, 3800 Cornucopia Way, Modesto, CA

Fee: $30 pre-conference; $35 at the door (evening session free)

Topics: This workshop will offer cutting edge information on sustainable landscape design, integrated pest management, drought tolerant plants, proven business strategies, creating habitat gardens and much more.

Information: Sarah Potenza, Ecological Farming Assoc. Watsonville, CA (831)763-2111)

To Register: Call the EFA Office (831)763-2111, or register online at www.eco-farm.org.

(DPR & CCA units applied for)