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 – dandgarden/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 spruce a.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