Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Spruce -- Rhizosphaera Needle Cast
 
Cause: Rhizosphaera kalkhoffii is the most prevalent cause although several other fungi (such as R. pini, Lophodermium sp., Lirula sp.) can cause needle cast diseases on spruce. The fungus overwinters in infected needles attached to the tree or on the ground. Rain-splashed spores spread to current-season needles. Shearing crews can also spread spores if foliage is wet. Infection re-quires long wet periods over 48 hours at optimal temperatures. Young trees may die if weather favors the disease several years in a row.

The disease has been described on Christmas trees in the eastern United States and has been a problem in Pacific Northwest nurseries and landscape trees. Colorado blue spruce and Engelmann spruce are highly susceptible; white spruce is intermediate; Norway spruce is relatively resistant. Other conifer hosts include pine, Douglas-fir, true fir, and western hemlock.

Symptoms: At first, current-season needles mottle yellow late in the summer. They soon turn brown or, on blue spruce, purplish brown. Brown needles are shed the next spring and summer. The fungus produces a fruiting body (pycnidia) which emerges from stomata. These small, black pycnidia are in rows on the underside of the needle. The disease is first on lower branches and gradually moves up the tree.

Current-season needles mottle yellow then turn brown or purplish brown.

Picea pungens with needle necrosis.
 
Cultural control:

  1. Use disease-free planting stock.
  2. Avoid shearing and other operations if foliage is wet.
  3. Avoid overhead watering in summer if plants will stay wet a long time.
  4. Remove dead needles underneath and within the tree.
Chemical control: Begin applying when new shoots are 0.5 to 1.5 inches long. Continue at 3- to 4-week intervals if weather stays very wet.
  1. Bravo Weather Stik at 5.5 pints/A. Daconil can be used in home gardens. 12-hr reentry.
  2. Echo 720 at 5.5 pt/A. 12-hr reentry.
  3. Kocide 2000 T/N/O at 0.75 to 3 lb/A (or 1 to 3 Tbsp/1,000 sq ft) dormant or at 0.75 to 2 lb/A when new growth is present. 24-hr reentry.
  4. Mancozeb-based products. 24-hr reentry.
    1. Pentathlon DF at 1 to 2 lb/A or per 100 gal water.
    2. Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
  5. Spectro 90 WDG (chlorothalonil plus thiophanate methyl) at 1 to 2 lb/100 gal water. 12-hr reentry.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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