This fungal disease of
spruce will cause holes in trees. The holes are not in the
trunkthey are areas of the tree canopy from which needles
have dropped. The needles have been cast from the tree;
thus, the name needle cast. Because spruce trees are not
able to form new needles where the old ones dropped, the
holes in the canopy are with the tree for its entire life.
The disease will not kill the tree, but it can cause enough
aesthetic damage that you might wish the tree had died. For
this reason, Rhizosphaera needle cast has become a disease
for which preventive fungicides have been recommended. As
long as entire branches are not killed, the new growth at
the branch tips can be protected from infection. As tips
continue to grow, the new growth may mask the defoliation
that has occurred on older needles near the center of the
This fungal disease is a particular problem on Colorado blue
spruce, but it may also infect other spruce species as well
as some pines. If you have had a problem with this disease
in the past, now is the time to take action. How do you know
you have had problems? The disease will cause first-year
needles to turn brown to purple in the fall. (Keep in mind,
however, that many environmental stress factors will cause
these same symptoms.) On trees with Rhizosphaera needle
cast, the affected needles may stay attached until the next
summer or fall.
Rhizosphaera needle cast may kill twigs if infection recurs
from year to year. Often the newest needles appear as green,
healthy tufts at the end of defoliated branches. When
infected needles are moist, the fungal pathogen will form
pinhead-sized fruiting structures (pycnidia) in neat rows on
the needles. To test for pycnidia, place affected needles in
a plastic bag with a wet paper towel; if present, pycnidia
should develop in one or two days. These pycnidia actually
protrude from the needle surface and are readily visible,
especially with a hand lens.
As with most fungal diseases, infection occurs in warm, wet
weather. With Rhizosphaera needle cast, spores are released
from spring until fall. Good air circulation will help
prevent infection, so prune surrounding plants to attain
better air movement, or consider removing crowded plants.
Fungicides are effective as a preventive control but must be
applied when needles are half elongated and again when fully
expanded. Keep an eye on the new growth on your spruce and
make the first application when new needles are half grown.
Chemical options are given on page 106 of the Illinois
Commercial Landscape and Turfgrass Pest Management Handbook,
1998–1999. Homeowner chemical options are listed on page 35
of the Illinois Homeowners’ Guide to Pest Management.