Thursday 19 June 2014

Needle Cast In Spruce

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.