Author: Farm Advisor
Date: 2001-11-15

University of California Cooperative Extension
Weekend Farmer
INYO AND MONO COUNTIES FALL 2003

207 W. SOUTH ST. OFFICE (760) 873-7854
BISHOP, CALIFORNIA 93514 FAX (760) 873-7314

BARK BEETLES
Bark beetles, family Scolytidae, are common pests of conifers and some attack broadleaf trees. Several hundred species occur in the United States. The most common species infesting pines in California are the western pine beetle, engraver beetles, and the red turpentine beetle. Cedar or cypress bark beetles attack cypress, and redwood trees. Oak bark beetles attack oaks and California buckeye. Shothole borer attacks damaged trunks of many tree species, including English laurel, fruit trees, and hawthorn. The European elm bark beetle feeds only on elms and vectors the Dutch elm disease fungus.
Life Cycle
Females lay small, oval, whitish eggs at the interface of the bark and wood. After eggs hatch, the tiny larvae mine galleries that branch out from the egg-laying gallery. At first the larval mines are very small, but they gradually increase in diameter as the larvae grow. The winding pattern of these galleries is helpful in identifying a bark beetle infestation and in distinguishing between the different species. Pupation occurs in enlarged chambers at the ends of the larval tunnels or in the outer bark. Pupae are usually whitish and occur within or beneath bark. Adults can emerge at any time of year, weather permitting, but emergence is most common in late spring and again in late summer to early fall. After emergence, adults generally disperse to attack susceptible trees elsewhere. Most bark beetle species have two or more generations a year in California, depending on temperature. The season of

attack is usually longer for species occurring in warmer locations, and they have more generations per year.
The bark beetles of economic importance mine the inner bark (the pholoem-cambial region) on twigs, branches, or trunks of trees and shrubs. This activity often starts a flow of tree pitch in conifers and is accompanied by a sawdust like material called frass. Frass accumulates in bark crevices or may drop and be visible on the ground or in spider webs. Small emergent holes in the bark with sap weeping out of the holes are a good indication that bark beetles have been present. Bark beetles commonly attack trees weakened or predisposed to infestation by drought, disease, injuries, or other factors that may stress the tree. Beetles can contribute to the decline and eventual death of trees but with a few exceptions usually are not the initial cause.
Management
Except for general cultural practices that improve tree vigor, little can be done to control most bark beetles beneath bark once trees have been attacked. Prune and dispose of bark-beetle-infested limbs. Promptly remove the entire tree if its main trunk is extensively attacked by bark beetles. Unless infested trees are quickly removed, large numbers of beetles can emerge and kill nearby trees if they are weakened or predisposed by other factors. Valuable, uninfected host trees near infested trees may be protected from bark beetles by spraying the trunk with a persistent insecticide in spring; however, do not substitute preventative sprays for proper cultural care.

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Properly prune infested limbs and remove and dispose of dying trees so that wood-boring insects do not emerge and attack other nearby trees. Timing of pruning is important. Do not prune elm trees from March to September or pines during February to mid-October. Do not pile unseasoned, freshly cut wood near woody landscape plants. Freshly cut wood and trees that are dying or recently have died provide an abundant breeding source for some wood-boring beetles.
Chemical Control
Unless trees are monitored regularly so that borer attack can be detected early, any spraying is likely to be too late and ineffective. Sprays will not kill larvae tunneling beneath the bark and must be directed at the adults as they bore into the trunk to lay eggs. If the tree was attacked during a previous year and no longer contains beetles because they have completed development and flown away, spraying that tree will provide no benefit and could kill beneficial insects. Seriously infested trees, or trees that are dead or dying due to previous beetle attacks, cannot be saved with insecticide treatments and should be removed. Systemic insecticides injected through the bark do not control or prevent attack by bark beetles or other wood borers.
Healthy specimen or high-value trees may be protected with an insecticide if they are near infested trees that are a source of beetles. Because each bark beetle species attacks only certain tree species (for example, pine bark beetles do not attack oaks and oak bark beetles do not attack pines) spray only healthy trees that are susceptible to the beetle species attacking nearby trees. It is not clear if products available to home gardeners can adequately prevent bark beetle attack. Most home gardeners also lack the high-pressure spray equipment and experience to effectively treat large trees. When hiring a professional applicator, discuss the specific pesticide to be applied.
Thoroughly drenching the main trunk with a pyrethroid (e.g., Dragnet) or the carbamate carbaryl (Sevin-Carbaryl) can prevent new bark beetle infestations if applied when adults are flying. Be sure to use a product labeled for trunk applications and apply it at the proper rate for trunk treatments.
(Continued on page 3)

Healthy trees are less likely to be attacked and are better able to survive the damage from a few bark beetles. Rapid, vigorous growth encourages host resistance.
Pay particular attention to old, slow-growing trees, crowded groups of trees, and newly planted trees in the landscape. Large nursery stock or transplanted trees, notably oaks and pines, can become highly susceptible to bark beetles after replanting. Transplanting success depends on the tree species and its condition, appropriate tree and site selection, characteristics of the planting site, the season of the year, the transplanting method, and follow-up care. Stresses placed on a tree caused by poor planting or planting at the wrong time of year, lack of proper care afterwards, or the planting of an inappropriate species for the site will increase the tree susceptibility to bark beetle invasion.
Biological Control
Woodpeckers, several predaceous beetles such as the black bellied clerid and a trogositid beetle, a predaceous fly, and parasitic wasps are natural enemies of the western pine beetle but rarely control it. Predators are more important in regulating bark beetle populations than parasites. When bark beetles attack and kill some trees, natural enemies are attracted and may eventually limit the infestation.
Cultural Control
Prevention is the most effective method of managing wood-boring insects; in most instances it is the only available control. Avoid injuries to roots and trunks and protect trees from sunscald and other abiotic disorders. Irrigation may be important during dry summer months in drought years, especially with tree species that are native to regions where summer rain is common. Also, dense stands of susceptible trees should be thinned to increase their vigor and ability to withstand an attack.
Irrigate when appropriate around the outer canopy, not near the trunk. Avoid the frequent, shallow type of watering that is often used for lawns. The specific amount and frequency of water needed varies greatly depending on the site and tree species (i.e., whether trees are adapted to summer drought or regular rainfall).

Sincerely,
Rick Delmas
County Director & Farm Advisor

MASTER GARDENER PROGRAM
Many people have requested having a Master Gardener Course. I have made initial contacts to have a University of California Advisor (s) who teaches the Master Gardener Program come to Bishop this coming spring and give a short course for people in Inyo and Mono Counties. The tentative plan is to hold the course/workshop on a Friday Evening and all day Saturday sometime in March of 2004. In order for us to have more insight into what subject matter people would like to see covered would you please complete the questionnaire and return it to the Farm Advisors Office, 207 West South Street, Bishop, CA 93514. (Fold in half, and place 37¢ stamp in right hand corner as indicated).
Rate the topics that are of most interest to you on a scale from 1-5 with 5 being the highest rating.
_____ Soil and Fertilization Management
_____ Water Management for the Garden
_____ Lawn Management: Watering, Fertilization, Diseases
_____ Plant Propagation
_____ Controlling Garden Pests Safely
_____ Plant Diseases
_____ Diagnosing Plant Problems
_____ Pruning
_____ House Plants
_____ Home Vegetable Gardens
_____ Entomology
_____ Weed Control
Other topics of interest to you: ______________________________________________________
To cover the expenses of the course (California Master Gardener Handbook - $30.00; travel expenses for presenter (s), and miscellaneous other expenses) the charge for the workshop will be $40.00. Are you willing to pay this amount for this course?
YES ______ NO ______
If NO, how much are you willing to pay for a Master Gardener Workshop? ______________
Name ________________________________________ Phone No. ___________________
Address _____________________________________________________________________
(Be sure to include your address if you want to be on our mailing list for workshop and Weekend Farmer Newsletter)

It is also believed that mite eggs are easier to kill in the late winter, as the shells become thinner when they approach hatching.
Plums and prunes occasionally tend to be susceptible to oil injury when treated in the dormant period. Plums and prunes should be treated in the delayed dormant period to avoid injury.
Walnuts are very easily damaged by dormant oil treatments. Therefore, if oil is used, it should be applied at the very end of the delayed dormant period, or better yet, at the time local experience shows it to be appropriate. Any deciduous tree suffering from lack of sufficient moisture may be more susceptible to dormant oil injury. Irrigate deeply before oil sprays and apply superior oils to eliminate this problem.
There are four types of spray oils:
dormant emulsive oil, a clear 98% oil;
dormant oil emulsion, a white, mayonnaise-like 80% oil that is somewhat safer than dormant oil;
original supreme type oil, a slightly safer oil that can also be used during the growing season; and
superior or narrow range oils that are even safer (because they are purer) and can also be safely used throughout the growing season.
The old true dormant oils (1 and 2) are still available in some areas. The old Volck Supreme, now difficult to find, is the best example of type 3. The new Volck Supreme oil, which confusingly has the same name, closely fits into the No. 4 category. In recent years, this latter group of narrow range type of oils has expanded its number of available label formulations which are mostly made from Exxon’s Orchex 796 and Unocal PGSO-2 base stocks. Other petroleum companies are also involved.
In summary, dormant spraying is strongly encouraged as being the most efficient and economical treatment of the season. The only reasons for not treating in the dormant season are lack of knowledge of its value, economics, or no pests present. Concerns about chemically disrupting any natural balance in the garden are sometimes expressed by homeowners. However, dormant treatments do not seem to be a factor and the overall benefits are great.
Adapted from Hortscript No. 17, September 1995.

Remember that treatments must be applied to kill adults before they lay eggs. Treatment at any other time will not be effective. Spray the bark in spring when beetles begin to emerge, which is in early spring in warm areas of the state and late spring in cooler and high elevation areas. Depending on local conditions and the pesticide used, a second application may be needed several months later to provide season-long control.
Insecticide sprays are not recommended against shothole borer and cedar or cypress bark beetles.
DORMANT SPRAYING OF FRUIT TREES IN THE GARDEN
John Dibble, Entomologist Emeritus, and Richard L. Coviello, Farm Advisor, Fresno County
Dormant sprays allow:
a wide period of time for application;
a broad range of useable materials;
a maximum unobstructed spray coverage;
multiple pest targets; and because of minimum risk of phytotoxicity and beneficial organism disruption, they become the most economically sound treatment of the entire season.
The properly applied combination of a selected insecticide and spray oil provides control of the peach twig borer (found on all stone fruit and almonds), and numerous other insect pests, including San Jose scale, eggs of European red mites and aphids. Addition of a fungicide to dormant oil sprays will help control some diseases, such as peach leaf curl. Although often present on certain fruit and nut trees, over-wintering codling moths, oriental fruit moths, and pacific or two-spotted spider mites are not affected by dormant treatments.
The time for dormant treatment, which can successfully control much of the residual pest population in the garden, is from late November through mid-February. If pre-bloom bud cracking has not yet occurred and bee kill is not a problem, dormant oil could be applied later in February through March (“delayed dormant period”).

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UNIVERSITY OF CALIFORNIA
COOPERATIVE EXTENSION
INY0 & MONO COUNTIES
207 W. SOUTH STREET
BISHOP, CA 93514

University of California Cooperative Extension
Inyo & Mono Counties
207 W. South Street
Bishop, CA 93514

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In this issue:
Bark Beetles
Life Cycle, Management, Biological, Cultural and Chemical Control
Dormant Spraying of Fruit Trees in the Garden
Why you should use them and types available
Master Gardener Program
Are you interested in attending a Master Gardener Course? Be sure and return the questionnaire