Print
E-mail
Comment
Rate
Bark Beetles Wreak Havoc On Trees
By Cynthia Bergman
Extension Horticulture Educator
Bark beetles, family Scolytidae, are common pests of conifers and some attack broadleaf trees. Several hundred species occur in the United States.
Adults are small, cylindrical, hard-bodied beetles about the size of a grain of rice. Most species are dark red, brown or black. Larvae of most species are off-white, robust, grublike and may have a dark head.
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.
Adults can emerge at any time of year, weather permitting, but emergence is most common in late spring. After emergence, adults generally disperse to attack susceptible trees elsewhere.
A buckshot pattern of holes is apparent on infested branches or on the trunks where the new adults have emerged. Larval galleries of all species are packed with sawdust-like boring dust called frass and most radiate out perpendicularly to the parent tunnels.
DAMAGE
The bark beetles mine the inner bark 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 sawdustlike material (frass).
Frass accumulates in bark crevices or may drop and be visible on the ground. Small emergence 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 they are not the initial cause.
MANAGEMENT
Except for general cultural practices that improve tree vigor, little can be done to control most bark beetles 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 host trees if they are weakened or predisposed by other factors.
Valuable, uninfested 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 preventive sprays for proper cultural care.
Plant only species properly adapted to the area. Learn the cultural requirements of trees, and provide proper care to keep them growing vigorously. 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.
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’s susceptibility to bark beetle invasion.
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).
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; avoid creating fresh pruning wounds during the adult beetles’ flight season. 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 have recently died provide an abundant breeding source for some wood-boring beetles. Tightly seal firewood beneath clear plastic in a sunny location for several months to exclude attacking beetles, and kill any beetles already infesting the wood.
Plant resistant species where bark beetles have been a problem. For instance, engraver beetles and red turpentine beetles do not attack redwoods or atlas cedars.
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. No insecticide kills larvae tunneling beneath the bark. Systemic insecticides implanted or injected through the bark or applied to soil beneath trees do not control or prevent attack by bark beetles.
Treatment must target the adults by spraying the bark so that they are killed when they land on trees and attempt to bore into the bark 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.
Healthy specimen or high-value trees may be protected with an insecticide, but most home gardeners lack the high-pressure spray equipment and experience to effectively treat larger trees. Effective products may not be available to home users, but are available to licensed pesticide applicators. When hiring a professional applicator, discuss the specific pesticide to be applied.
Thoroughly drenching the main trunk with permethrin or carbaryl can prevent new bark beetle infestations if applied when adults are flying, usually April and May. In our area spraying must be completed before mid June. Be sure to use a product labeled for trunk applications and apply it at the proper rate for trunk treatments. Treat all branches more than 1 inch in diameter. Label rates for foliage treatments will not be effective.
Regardless of the insecticide used, always read and follow label directions! Mix only what you need to avoid leftovers. Leftover chemicals should never be poured down a sink or storm drain. Take special care to keep pesticides from running off-site and into drains or waterways.
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, late April to early June.
Information from University of California Agriculture and Natural Resources Publication 7421, Pest Notes: Bark Beetles, available online. Also from Dr. John Ball, State Forestry Specialist, Conifer Insects Control Recommendations.
Adults are small, cylindrical, hard-bodied beetles about the size of a grain of rice. Most species are dark red, brown or black. Larvae of most species are off-white, robust, grublike and may have a dark head.
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.
Adults can emerge at any time of year, weather permitting, but emergence is most common in late spring. After emergence, adults generally disperse to attack susceptible trees elsewhere.
A buckshot pattern of holes is apparent on infested branches or on the trunks where the new adults have emerged. Larval galleries of all species are packed with sawdust-like boring dust called frass and most radiate out perpendicularly to the parent tunnels.
DAMAGE
The bark beetles mine the inner bark 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 sawdustlike material (frass).
Frass accumulates in bark crevices or may drop and be visible on the ground. Small emergence 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 they are not the initial cause.
MANAGEMENT
Except for general cultural practices that improve tree vigor, little can be done to control most bark beetles 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 host trees if they are weakened or predisposed by other factors.
Valuable, uninfested 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 preventive sprays for proper cultural care.
Plant only species properly adapted to the area. Learn the cultural requirements of trees, and provide proper care to keep them growing vigorously. 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.
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’s susceptibility to bark beetle invasion.
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).
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; avoid creating fresh pruning wounds during the adult beetles’ flight season. 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 have recently died provide an abundant breeding source for some wood-boring beetles. Tightly seal firewood beneath clear plastic in a sunny location for several months to exclude attacking beetles, and kill any beetles already infesting the wood.
Plant resistant species where bark beetles have been a problem. For instance, engraver beetles and red turpentine beetles do not attack redwoods or atlas cedars.
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. No insecticide kills larvae tunneling beneath the bark. Systemic insecticides implanted or injected through the bark or applied to soil beneath trees do not control or prevent attack by bark beetles.
Treatment must target the adults by spraying the bark so that they are killed when they land on trees and attempt to bore into the bark 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.
Healthy specimen or high-value trees may be protected with an insecticide, but most home gardeners lack the high-pressure spray equipment and experience to effectively treat larger trees. Effective products may not be available to home users, but are available to licensed pesticide applicators. When hiring a professional applicator, discuss the specific pesticide to be applied.
Thoroughly drenching the main trunk with permethrin or carbaryl can prevent new bark beetle infestations if applied when adults are flying, usually April and May. In our area spraying must be completed before mid June. Be sure to use a product labeled for trunk applications and apply it at the proper rate for trunk treatments. Treat all branches more than 1 inch in diameter. Label rates for foliage treatments will not be effective.
Regardless of the insecticide used, always read and follow label directions! Mix only what you need to avoid leftovers. Leftover chemicals should never be poured down a sink or storm drain. Take special care to keep pesticides from running off-site and into drains or waterways.
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, late April to early June.
Information from University of California Agriculture and Natural Resources Publication 7421, Pest Notes: Bark Beetles, available online. Also from Dr. John Ball, State Forestry Specialist, Conifer Insects Control Recommendations.
 |
 |
|
| Scouting Enjoyable For Both Girls, Leaders | Baptisms |
Article Rating
Reader Comments
Submit a Comment
We encourage your feedback and dialog, all comments will be reviewed by our Web staff before appearing on the Web site.
Not registered yet?
