Plant Disease Control No. 7
Revised January 1998

Needle Blight of Evergreens

Needle blight is a non-parasitic disease of many of the ornamental evergreens grown throughout Utah. The disease occurs most frequently on spruces and pines but is also present on juniper, arborvitae, and yew. Needle blight is most often caused by drought, winter injury, sunscald and root rot. In most areas of Utah there is a low concentration of evergreens and therefore damage caused by infectious diseases is rare. Evergreens grown at high elevations are the only trees observed with fungal infections.

SYMPTOMS

Needle blight may first be noticed when an unusual number of needles begin to turn brown, red or purple. The blight may begin either at the tops or the bases of needles and may be on new or old needles (outside or inside needles of the tree respectively). When only the older or inner needles are affected and the new needles appear healthy then the condition is probably normal. Needle drop is an annual phenomenon in Evergreens (see Utah Plant Diseases bulletin No.11). Trees with needle blight may have so many needles affected that the whole tree will have a brownish appearance. Spruce trees will frequently have only a few isolated branches with symptoms. Severely affected trees may die after one or two seasons but if the growing conditions are corrected trees may respond and live for years.

CAUSE

The primary cause of the disease is an improper water supply but is also complicated by other factors such as soil conditions, adverse weather, or herbicides. Drought conditions or excessive soil moisture cause death of the fine feeder rootlets. Needle blight occurs when the delicate balance between the foliage of the tree and the feeder rootlets is altered. The combination of summer drought plus winter drying causes needles of spruces, especially the Blue spruce, to turn purple. Radical changes in irrigation procedures or timing may also cause needle blight.

CONTROL

Evergreens should be irrigated deeply during hot, dry, summer weather. The ground under evergreens should have soil moisture at least 4 ft. deep throughout the year to avoid drought. However, do not overirrigate. Excessively wet soils cause root rot. Maintain a natural mulch of fallen needles since it helps maintain soil moisture as well as protect the shallow roots from excessive heat. Avoid construction near trees which would destroy roots. Protect the trees from winter injury by irrigating all evergreens deeply in late fall and again in midwinter if the soil has dried out. Fertilize trees in the spring with nitrogen fertilizer. A balanced fertilizer such as 5-10-5 could also be used.

Sherman V. Thomson/Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician

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