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Browning needles in spruce trees

May 18, 2020
A thinned down spruce tree with several needles fallen off.
Rhizosphaera needle cast damage in spruce.

Spruce and coniferous trees are susceptible to environmental, insect and disease problems that can cause the trees to discolor, lose needles and possibly die. Spruce in both urban and rural landscapes can be affected.

Spruce trees can show brown needles starting from the lower limbs and progressing up the tree. One common needle disease in Minnesota, Rhizosphaera needle cast, is caused by the fungus Rhizosphaera kalkhoffii. Blue spruce varieties are very susceptible to Rhizosphaera. 

However, there is another needle cast fungus, Stigmina lautii that is infesting more species of spruce including white spruce. Trees that are stressed from drought, poor planting practices, or other factors are more likely to suffer from needle cast.

Symptoms of needle cast disease

Symptoms of needle cast may vary, but often needles turn brown or purplish brown late in winter or early spring. 

  • Older needles closer to the trunk of the tree become discolored and fall off mid-summer, leaving the tree looking thin and bare. 
  • Damage typically starts on the lower branches and moves up the tree affecting susceptible spruce trees when 15 to 20 years old. 
  • Close inspection using a hand lens will reveal tiny black dots on infected needles—stomata (tiny holes that allow gas exchange) are white on healthy needles.

Extension has a diagnostic tool to help diagnose tree and plant problems. Start at the main page and click on the links that are associated with your tree or plant symptom. 

To confirm a diagnosis, plant samples can be sent to the University of Minnesota Plant Disease Clinic. Some diseases are not present on the newest growth, so it's important to include older growth or transitional branch samples.

Protecting your trees

Fungicides with the active ingredient chlorothalonil, copper hydroxide, or mancozeb will protect new spruce needles from infection by needle cast diseases. Always read and follow label directions. 

  • Most labels recommend one application in spring or early summer (around May) when the new needles have grown to half their mature length. 
  • Then a second application 3 to 4 weeks later. 
  • Chlorothalonil-based fungicides may discolor spruce needles.  

Norway and Meyer spruce appears to show some tolerance to these needle cast diseases. To avoid disease epidemics it is advised to plant a diverse selection of trees, rather than planting 1 or 2 species. 

Consult our list of recommended trees in Minnesota, and talk to your local nursery for advice on planting for your specific landscape. 

Gary Wyatt, Extension forestry educator based in Mankato, Minn.

Related topics: Natural Resources News
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