Do your spruce
trees look like they have short pants? A little thin? You may have Needle Cast
Disease and not know it!
Evergreens
typically retain their needles for up to 3 years. If they are stressed or
suffering from drought or disease they can lose them in one season. The
investment the trees make in the needles costs them valuable resources and when
they lose them prematurely they begin a downward spiral that may lead to death.
Needle Cast
Diseases are fungi and in spruce trees they are generally two types,
Rhizosphaera needle cast or Stigmina needle cast. These are
caused by Rhizosphaera kalkhoffii, and Stigmina lautii respectively.These can be diagnosed by looking at the
fruiting bodies on infected needles with a microscope or strong hand lens.
Rhizosphaera fruiting bodies are rows of small smooth edged black dots coming
out of the stomata, tiny breathing holes, on the browning needles. Stigmina
fruiting bodies are black, in rows and are not as round or clearly defined as
Rhizosphaera.
Infected needles
will turn bronze and be dropped prematurely. This needle drop causes the tree
to decline and look sparse. Eventually the tree may die. Wet humid conditions
and lack of air flow all increase the chance of this disease spreading and
damaging your trees.
Chemical fungicides
are effective in controlling this disease. They must be applied according to label
directions and typically two or three applications are required. When the
needles are half elongated and when they are fully elongated is the recommended
timing. These treatments will need to be applied on a yearly basis for several
years until the plants recover. In the case of Stigmina this may be needed
yearly.
Avoid watering on
the foliage, keep groups of trees spaced well to increase air flow. Prune out
dead branches and remove badly affected trees to limit the spread of the
disease.
If you have
questions Certified Arborists are industry recognized experts in plant insect
and diseases control. Contact your I.S.A. Certified Arborist to see if you think
you have this damaging plant disease.
