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Insects & Diseases
Forests in California are host to a variety of insects and disease-causing plant pathogens that are native to that ecosystem and play valuable roles in the healthy function of the forest. In some cases, these native species must be addressed by forest managers on a local or regional basis.
For more information on non-native insects and disease please visit our Invasive Species page.
A Field Guide of Insects and Diseases of California is in development.
Diseases
Heterobasidion occidentale and Heterobasidion irregulare (previously known together as Heterobasidion annosum and prior to that as Fomes annosus) are root-rotting fungi that cause a tremendous amount of growth loss and death of coniferous species in California.
Several links are provided below which include information about the disease and how to effectively manage it.
General Information:
- Heterobasidion map: point locations indicate areas where annosus root disease has been reported in R5
- Forest Health Protection Handbook, FSH 3409.11, Chapter 60
- Otrosina Heterobasidion taxonomy paper
- Borax: Frequently Asked Questions
Management and Treatment:
Insect Pests
Bark & Ambrosia Beetles
Native insects are important agents of change in forest ecosystems. They affect tree growth, influence species composition, stand structure, and ecological succession of forest stands. Some insects are vectors of pathogens that cause disease.
- Bark Beetles in California Conifers: Are your trees susceptible?
- Bark and wood boring beetles of the world
- Bark beetles and vegetation management
- 2011 Western Bark Beetle Strategy
- Western Forest Insects – Bark Beetles
This beetle is native to western North American forests and primarily attacks ponderosa and Coulter pines in California. During drought periods it can kill trees of all ages and vigor classes. Group killing of trees is common. Adult beetles are dark brown and about ¼ inch long. Larvae are small, white, legless grubs. Western pine beetle larvae mine a short gallery in the phloem and then turn into the bark to complete their development.
The mountain pine beetle is native to forests of western North America and attacks ponderosa, lodgepole and most five-needle pine species. Periodic outbreaks of mountain pine beetles in lodgepole pine forests can kill millions of trees. Biggest impacts in California are to sugar pine, high elevation 5-needle pines, and lodgepole pine.
A native bark beetle, this species targets true firs, primarily red and white fir in California; it does not attack Douglas-fir (not a true fir). Fir engraver prefers drought stressed, injured, or diseased trees but will also attack trees already infested by other damage agents (ex: Douglas-fir Tussock Moth). During and after periods of below-average precipitation, beetle populations can reach high levels that cause widespread mortality.
Native pine engraver beetles (often referred to as Ips) primarily attack cut green pine limbs and tops from pruning and thinning treatments, windthrown trees or trees subjected to snow breakage. They also infest pines attacked by other bark beetle species. During periods of drought, they can attack and kill smaller pines that are experiencing extreme moisture stress. Larger pines are often only top-killed, a common signature of pine engraver attack.
California fivespined ips (Ips paraconfusus) Forest Insect and Disease Leaflet
Pinyon ips are the primary native bark beetle that attack pinyon pines. During extreme periods of drought, large areas of pinyon can be killed by this species. Like other Ips spp., it also infests green slash and can be a concern when thinning and pruning trees. This beetle is also attracted to pinyons with prior infections of root disease.
Jeffrey pine beetle is the principal insect enemy of Jeffrey pines. This native beetle occurs throughout most of the range of Jeffrey pine, and similar to the mountain and western pine beetle, it can cause high levels of tree mortality. This beetle prefers mature or larger diameter trees, but will attack smaller diameters during epidemics.
Woodborers
This native woodboring beetle species is most often a colonizer of dead and dying trees that have succumbed to other insects, fire or disease. However, during periods of extreme drought, they can attack and kill moisture stressed pines of all sizes. California flatheaded borer has been observed killing Jeffrey, ponderosa and sugar pines. Attacks can occur over several years before tree is killed.
Defoliators
This native moth is most destructive to white, grand, and Douglas-fir trees in California. Trees can be lightly to severely defoliated by this moth, which may result in direct mortality or subsequently be killed by other damage agents. Outbreaks are cyclical: arising every 7-10 years on average in California, subsiding after 3 years. Most of the damage occurs during the building phase, when larval stages are defoliating new and older needles.
Additional Resources
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REPORT A PEST!Please report a plant or pest that you suspect may be a new invasive species in your area. -
View images of forest insects and diseases at forestryimages.org.