Dutch Elm Disease• Ophiostoma ulmi

(syn. Ceratocystis ulmi)

Dutch Elm Disease

• The American Elm is very susceptible

• Transmitted by elm bark beetles and root grafting

• Yellowing and wilting of branches in the crown of the tree

• Brown streaks in water conducting tissues

Dutch Elm Disease Control• Sanitation of wood

– Remove dead or dying trees

• Bark beetles survive in wood piles– Burn or de-bark wood

• Manual trenching or Vapam

• Plant resistant elms– http://www.extension.umn.edu/projects/

yardandgarden/ygbriefs/p425dutchelm-resistant.html

Fire blight• Erwinia amylovora

• Apple, pear, mountain ash, raspberry, contoneaster

Fire blight control• Avoid highly susceptible cultivars and

rootstocks• Prune out blighted shoots (and sanitize

equipment) early – Scout after petal fall– Cut at least 8-12 inches below visible infection site

• Don’t fertilize to promote growth• Bacteriacides are available, generally not

effective– Can only prevent bloom infection (rare in MT)

Brown felt blight• Herpotrichia juniperi and Neopeckia

coulteri

• Small trees buried under snow

Brown felt blight control

• Usually none is warranted

• Causes some growth loss

• For ornamentals, foliage sprays of 5% Zineb or Maneb applied before first snowfall are effective in control.

Cytospora canker of sprucea.k.a. Leucocytospora canker, Valsa canker

• Enters branches through wounds

• Spread by pruners, rain splash, animals

Cytospora canker of spruce

• Prune affected branches back to the collar at the trunk

• Sanitize tools!– Rubbing alcohol or 10% bleach

Rhizosphaera needle cast • Rhizosphaera kalhkoffii

• Rainsplash dispersed

• Symptoms:– Reduced needle retention– Dead (brown) older needles– Healthy, new needles do not show signs of

infection

Rhizosphaera needle cast control

• Plant healthy trees• Good air flow in canopy• Don’t plant next to established (and/or

infected) trees• Bordeaux mixture or chlorothalonil (Daconil)• Spray in early June (new needles ½ length)

and again 3 wk later (new needles full length)

Abiotic tree diseases• Drought: cottonwood and willows have

shallow root systems; will shed small branches and twigs

• Trees will shed leaves and needles to prevent water loss

Drought recommendations• Slowly water affected trees regularly until mid-

August, then again following a killing frost• Do not water late into October; allow the tree

to complete the winter hardening process• Apply 5 to 10 gallons of water for each inch of

trunk diameter and the water should be applied within the radius of half the tree’s height.

• Do not fertilize