Forest Insects and Disease

Sharon Paul USDA FS Forest Service Lincoln National Forest

High stand density

Horse Thief Basin, Prescott NF, 2002

Piñon Outbreak in 2002

West of Cochiti Lake, NM

Piñon Mortality

Near Mesa Verde, CO

East of Flagstaff,

AZ

Looper, Nepytia janetae.

Larva, adult and landscape damage.

Douglas-fir tussock moth, Orgyia pseudotsugata. Larva, larval feeding, tree damage and adults (male on left, female on right is flightless)

Western spruce budworm, Choristoneura

occidentalis. Larva, adult, landscape damage and cycles.

Western tent caterpillar, Malacosoma californicum. Larva, adult with egg mass and larva with stand damage.

Symptoms of bark beetles attack • Crown fading

• Pitch tubes/streaming

• Boring dust

• Woodpecker activity

Roundheaded pine beetle, Dendroctonus

adjuntus. Galleries and adult. Flights in the Fall

Western pine beetle, Dendroctonus brevicomis. Larval development in outer bark, woodpecker

activity

Ips

WPB

Ips pini in ponderosa pine showing small groups of trees attacked.

Pinyon ips, Ips confusus. Adult,

galleries, pitch tubes and landscape

damage.

Douglas-fir beetle, Dendroctonus

pseudotsugae.

Galleries, adult beetle and tree damage.

Blue Stain Fungi

Suppression

Treatment of infested trees

• No sprays available for treating infested trees

• Solarization – infested logs covered w/ plastic

• Chipping, burning, peeling

• Removal from site: disposal or sanitation

Prevention of Beetles

• Silvicultural strategies to reduce tree density and favor non-host trees

• Must manage thinning slash

• Avoid stacking green firewood or infested wood next to standing pine

Preventative watering • Water most valuable trees

• Water to 2-3 feet deep once per month during dry months

Watering zone

Drip line

Preventative sprays

• Preventative sprays are available

• Sevin SL, Astro, Permethrin Plus C

• Spray must be applied up entire trunk to 4 inches in diameter

• Sprays work about one year

ag.arizona.edu/extension/fh/pdf_files/preventative_spraying.pdf

Dwarf Mistletoe

Dwarf Mistletoe (Arceuthobium) • An obligate parasite- must have a live host.

• Leafless.

• Always grow on conifers.

• Spread by explosive seed.

– Distribution in stands is usually “patchy,” due to the means of spread

– Rate of lateral spread: 1-2 feet year • All ages and sizes of trees are susceptible

Witches’ Brooms

RMRS photo

RMRS photos

July - August

Shoots first appear 2+ years later.

Fruits mature after 2+ more years and the life cycle starts again.

A swelling appears in about 2 years.

They germinate and infect the twig

Rains wash them onto the twig

Dwarf Mistletoe Lifecycle

Note: Life cycle takes a minimum of 6 years. Latent period may be 4 to 10 years !

DM Distribution in the SW

Over 1/3 ponderosa pine acres infested

Over 1/2 mixed conifer acres infested

Biotic associates

• Birds and squirrels often use witches’ brooms as nesting platforms

• Higher snag densities in infested areas provide habitat for some birds

• Several insects feed on dm plants; these in turn attract insect-feeding birds

• Feeding by birds on dm itself is probably uncommon

Effect on tree growth:

DMR 1–3 none

DMR 4 10-20%

DMR 5 20-30%

DMR 6 30-100% (dead tree)

On average, a tree’s DMR increases every 10 years.

Can we control mistletoe? Yes, it is possible to control them silviculturally because: 1) they are obligate parasites and 2) they spread relatively slowly

However, controlling them is not easy, because of 1) latent infections and 2) relatively rapid intensification after thinning

Releasing the trees releases the “toe”

Sanitation Thinning

Seed-Tree Cut

Shelterwood Cut

Patch Clear-cut/Group selection

Underburning can reduce dwarf mistletoe infection via scorch pruning and mortality of heavily-infected trees

White Pine Blister Rust

White pine blister rust Cronartium ribicola J. C. Fisch.

Native to Asia, introduced to North America ~turn of the 20th century In at least 38 states Hosts: SW white pine. Limber pine and bristlecone pine also susceptible. Alternate hosts: Currants and gooseberries (Ribes) spp.

The “Discovery Tree” of white pine blister rust on the LNF in 1990?

White pine blister rust life cycle

Two obligate hosts

Infected Ribes spp., no mortality

Infected 5-needle pines, mortality

Aeciospores in the spring

Basidiospores in the fall

Effects of White pine blister rust. Powdery urediniospores for cycling

Effects of White pine blister rust.

Dead branch “flagging”

Mortality in small trees

Branch flagging and mortality in larger trees