The Green Scene May 2012 tips for saving water in landscape irrigation

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he Green Scene

May 2012


We are entering summer, the time of highest water use for plants in landscapes, orchards, and gardens. Almost all plant species need summer irrigation in Kern County landscapes, but too much irrigation can be as detrimental as too little. To maintain plant health and manage costs for outdoor water use, here are a few tips to consider.

It’s helpful to walk through the irrigation system while it is running, perhaps every month, to check for coverage, to prune back plants that may block nozzles, to see that all valves come on and turn off, and that sprinkler heads are operating. Sometimes a pop-up head will need to be readjusted for height, or a taller sprinkler head substituted. Sometimes dirt plugs the nozzle so cleaning is needed.

The best time to irrigate in most home situations is dawn, or about 4-6 a.m. That is when winds diminish and temperatures are lowest so water does not blow away or evaporate quickly. Evening irrigation can lead to leaf diseases if water is allowed to stand on foliage during the night. During exceptionally warm weather, it is certainly okay to irrigate in the afternoon to cool turfgrass or give plants extra water. Water droplets do not focus the sun’s rays and cause leaf burn.

A rule-of-thumb is to irrigate to fill the root zone, and that implies water delivery sufficient to penetrate soil several inches to several feet, more easily accomplished in agriculture than in home landscapes. After irrigation, one can check water penetration with a screwdriver or a garden trowel or shovel. Frequent short irrigations can lead to shallow root systems with little capacity to withstand dry conditions. Keeping plants wet can lead to root rot in many woody species.

Irrigation scheduling is about frequency and duration, how often valves come on and the length of time each valve remains open. In general, it is best to set duration for each station so as to fill the root zone and then to add or subtract days depending on the season.

Home water bills often contain information, such as a bar chart, showing water use over the past year. Plant water needs in the southern San Joaquin Valley vary by about a factor of 10 during the year, with water needs almost zero in the winter months. If irrigation is turned off during winter, one can see what the indoor water use was during that period. If irrigation is matched to season there will be a climb in spring, highest water use in summer, and a decline in autumn. If the water bill shows the same amount of use for all 12 months, it is likely plants are being over-irrigated most of the year.

For the engineers among us, the baseline water use rate for plants in the Bakersfield area is about 0.25 inches per day in July—that’s the average but daily use can be higher if temperatures are well over 100°F or drying winds are present. For the Ridgecrest or Mojave areas, the baseline can be 0.30 inches per day. Those values do not imply that 0.25 inches of water need be applied every day, but that value does allow us to estimate water needs over period of days or weeks. One can calculate the water needed by a landscape by measuring the square feet of the landscape and multiplying by water use as a depth, and then converting to volume with the appropriate unit conversions. By doing so and comparing with a water bill we can quickly see if we’re about right in terms of water applied.


Although we don’t have a volunteer Master Gardener program in Kern County, we continue to offer annually a series of classes about the horticulture of landscapes, orchards, and gardens. In response to inquiries, we plan to offer our level 1 class beginning latter August, 2012. I haven’t decided about what other class we might offer, so vote for your preference by giving me a call or sending an email. Please contact us in July or look for announcements giving specific starting dates.

Opportunity to Visit Chernobyl, Ukraine

After the reactor accident in 1986, Chernobyl in Ukraine became one of the world's case studies on the intersection of radiation and the environment.  There is a lot of activity in the “Zone” these days, and government has opened the area to visitors on a supervised basis. Much of the flora and fauna is returning.  I’ve desired a visit to that area for some time, and now am planning such a visit. I want to offer others the opportunity to come along.  It’s not a place most of us would visit on our own, and a group setting offers advantages.

Our guide at Chernobyl will be Sergii Mirnyi, who was a radiation control officer working in the Zone right after the accident, and has been involved there since.  He has very good scientific credentials with an M.S. in physical chemistry and an M.S. in environmental science, and he speaks English well.

Our plan is to arrive in Kiev, Ukraine, Sunday, Sept. 2. Monday, Sept. 3, is a day to adjust to the time zone and see a few sights around Kiev, a notable city with a history dating from the 400’s. Monday is also a buffer in case of flight delays. We are reserving a tour to Chernobyl departing early Tuesday morning, Sept. 4, and returning in the evening, Sept. 5. Thursday is an optional day to remain in Kiev or depart for other destinations in Europe or back to the U.S.

Please contact me for more information on the scientific content pertaining to this visit, or 661 868-6220.


Borers are perhaps the most common type of insect problem in woody shrubs and trees in the landscape in Kern County, and in deciduous trees in home orchards. Sap on branches or sawdust-like frass are indications borers may be present. (Termites also produce frass, but do not feed on live wood.) This article attempts to summarize the common borer species and their landscape plant hosts in the Kern County area, but does not consider forest pest problems due to bark beetles.

There are a half-dozen common borer species with varying biology, but the predisposing factors for attack are similar. Plant injury from drought stress or sunburn may lead to borer attack. Plants that are overmature or declining in vigor may become susceptible, and some plants (e.g. poplars, willows, ‘Hollywood’ juniper) are inherently susceptible despite good management. The common denominator for resistance is plant vigor, since borers cannot invade a healthy plant with good sap flow. Insecticide treatments are, in general, distant second or third choices for managing borers due to insect biology and chemical characteristics. Currently registered insecticides, including systemic materials, are not effective in borer management in the landscape.

Tree borers are larvae of either beetles or moths. The adult lays eggs on the bark surface, and is often attracted to roughened bark and probably also to plant-produced volatile compounds that result from injury. The eggs hatch and the larvae tunnel into phloem tissue. If wood is healthy, sap flow occurs and larvae are “pitched out,” i.e. smothered by sap and expelled from the wood. If not, the larvae feed and go through successive molts, finally forming a pupa inside wood. After a time, the adult emerges from the pupal case and chews its way out of the plant—the holes seen from borers are the exits, not the entrances. Total time for a generation may be measured in weeks, months, or sometimes years, depending on the insect species and weather conditions.

Because borer larvae feed mostly in phloem tissue—that’s where the sugars are—and systemic insecticides tend to be xylem-transported, the lack of contact with the insect makes them ineffective. Also, sufficient concentrations of insecticide would be needed to reach the feeding larvae, a difficult proposition for systemic materials used safely. Most borers have long egg-laying periods, so timing of insecticide applications was and remains problematic. In the past, persistent (e.g., chlorinated hydrocarbon) insecticides such as lindane were sometimes applied to bark surfaces to try to interfere with entrance of larvae into wood. The persistence of the insecticide could sometimes compensate for the timing problem, but such persistent insecticides often pose environmental problems and have therefore been removed from the market. Therefore, insecticide treatments do not make sense considering both chemical properties and insect biology.

Borer management focuses on prevention, the most important strategy by far. Careful tree species selection is a key, since some species are quite susceptible to borer attack despite good management. Protection from sunburn, for example use of white latex paint, is important, especially for young fruit trees and others with thin bark. Sanitation in the form of removal of dead limbs and badly infested trees will also help. However, borer adults fly, so removal of infested wood in a landscape does not prevent invasion of a susceptible plant. Also, the resistance of a plant is more important than the proximity of a borer source. Borers do not reside in soil, so replanting trees in the same places is not a problem from that standpoint. As a practical matter, removal of damaged trees and replanting is often a more effective approach than trying to coax a debilitated plant back into vigor.

Some common borers in Kern County:

Pacific flatheaded borer (Chrysobothris mali) is the larva of a buprestid beetle, and hence has a flat head. The adult makes D-shaped exit holes. It is often found in home fruit trees such as cherry, plum, peach, and nectarine that have been damaged from sunburn, drought-stress, or are overmature. Improper pruning can lead to sunburn in these and other trees having thin bark. Leaving trees without water, as may occur if a property goes through foreclosure, often results in ruin of a home orchard. These fruit tree species often develop borer problems if the tree is more than 15 years old. If borer damage is extensive, the better course is to remove and replace fruit trees rather than trying to restore them to vigor. Shade trees are generally resistant, but mimosa trees are susceptible if the wood on top of branches becomes sunburned.

Shothole borer (Scolytus rugulosus) adults are small scolytid beetles making exit holes the size of shot pellets, small and numerous. The host range includes home deciduous fruit trees, and damage occurs under conditions similar to those for Pacific flatheaded borer.

Western poplar clearwing moth larvae (Paranthrene robiniae) are often found as a borer in poplar and willow species. Most willows and poplars are inherently susceptible to this insect despite sufficient irrigation. The larvae cause galls to be formed on small branches and cause swelling on trunks. Trees may coexist with insect despite the damage, since both willows and poplars grow rapidly and can replace damaged tissue.

Phloeosinus sp. is a small beetle whose larvae can cause extensive damage to cypress trees. Overmature or under-irrigated trees are susceptible.

Carpentermoth (Prionoxystus robiniae) is often found in overmature ‘Modesto’ ash trees. The larva is relatively large, and the exit holes may be ¼ inch in diameter. Dead wood and sawdust-like frass, the exit holes, and branch decline all accompany attack of this insect.

Juniper twig girdler (Periploca nigra) is found in juniper stems that have been sunburned, and in susceptible varieties like Juniperus torulosa ‘Hollywood.’ This variety is now rarely planted, but older 10-15 ft plants may be found throughout Kern County.

The eucalyptus longhorned borer has arrived in the Bakersfield area. The species responsible for damage in recent years is Phoracantha recurva, which first arrived in Southern California in 1995. The adult stage of the insect is a longhorned beetle whose antennae are longer than the body of the insect. The beetle is black with a cream-colored zigzag band across its wing covers. The adult female lays eggs in groups of 3-30 under loose bark of eucalyptus trees where the eggs hatch, and larvae begin to chew their way into the outer phloem tissue, feeding and molting, until they are more than an inch in length. Larvae require about 70 days in trees to finish feeding, and the entire lifecycle in summer takes about 3-4 months. The oval exit holes are 3/8 – ½ inch in diameter (long dimension of the oval). Eucalyptus branches or entire trees can be killed when larval feeding girdles the tree. Eucalyptus species differ in susceptibility with Eucalyptus diversicola, E. globulus, E. nitens, E. saligna, and E. viminalis susceptible; while E. camaldulensis, E. cladocalyx, E. robusta, E. sideroxylon, and E. trabutii are resistant. Signs that a tree is under attack include areas of peeling or missing bark, sawdust-like frass, concave troughs parallel to the limb surface, and exit holes in limbs.


Dreistadt, S.H. 1994. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. UC Agriculture and Natural Resouces Publication 3359, second edition.

Paine, T.D., Dahlsten, D.L., Millar, J.G., Hoddle, M.S., and L.M. Hanks. UC scientists apply IPM techniques to new eucalyptus pest. California Agriculture 55: 8-13.

The UC Statewide IPM Program is pleased to announce the publication of its latest issue of the UC IPM Green Bulletin. The May 2012 issue is posted at This issue features articles such as Using Lure Traps to Reduce Yellowjackets Around Picnic Areas, Herbicide Resistance--Should You Be Worried?, plus an announcement of the new Pest Note Removing Bee Swarms and Established Hives. As always, the UC IPM website,, offers access to peer-reviewed information for many disease, insect, and weed problems.

John Karlik

Environmental Horticulture/Environmental Science

Disclaimer: Discussion of research findings necessitates using trade names. This does not constitute product endorsement, nor does it suggest products not listed would not be suitable for use. Some research results included involve use of chemicals which are currently registered for use, or may involve use which would be considered out of label. These results are reported but are not a recommendation from the University of California for use. Consult the label and use it as the basis of all recommendations.

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