Needlecast Diseases of Pine and Spruce

OMAF Nursery - Landscape Series

Table of Contents

1. Introduction
2. Rhizosphaera Needlecast of Spruce
3. Lophoderium Needlecast of Pines
4. Conditions Favouring Needlecast Diseases
5. Control

Introduction

Needlecast diseases of pines and spruces are fungus diseases affecting the newly elongated needles of the current season's shoots. Symptoms usually appear in the winter or spring following infection and needles drop or are "cast" leaving only a single year's compliment of needles. Before being "cast", infected needles develop chlorotic spots that rapidly turn tan to reddish brown. Black-brown fruiting structures develop on needles from mid spring to early summer. They are oval or football in shape and open longitudinally to release spores. When needles are wet, they are easily visible to the naked eye. There are several different fungi which can cause needle cast. Needlecasts caused by Rhizosphaera kalkhoffii and Lophodermium seditrosium are commonly found in landscape conifers

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Rhizosphaera Needlecast of Spruce

Causal agent:

Rhizosphaera kalkhoffii

Host plants:

Picea pungens "Glauca", Colorado blue spruce, very susceptible; P. abies, Norway Spruce, P. mariana, black spruce, P. omorika, Serbian spruce seem to be resistant. Pinus mugo, mugo pine; P. nigra, Austrian pine; P. strobus, white pine. Pseudotsuga menziesii, Douglasfir; Abies concolor, silver fir.

Life cycle:

Current season's needles become infected by spores released from overwintering fruiting bodies, pycnidia, on last year's needles or from needles on the ground. Spores are dispersed by splashing and dripping water in the spring through until autumn. Both current needles and those which are stressed by either other pathogens or environment are susceptible to attack. Infections usually start on lower branches and spread upwards into the tree. If the disease starts higher in the tree, and spreads down or up, defoliated branches may appear among healthy ones. During late summer and early autumn, needles that were infected in the spring become yellow and mottled in appearance, eventually turning brown. In blue spruce, needles turn a purplish brown colour. Browning of infected needles occurs during the winter and early spring. Twelve to fifteen months after the infection occurred, needles fall leaving only the current season's compliment of needles.

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Lophoderium Needlecast of Pines

Causal agent:

Lophoderium seditiosium. There are other species of Lophoderium however they are mostly weak pathogens usually attacking plant tissues which are already stressed or injured. L. seditiosium is a virulent or aggressive pathogen infecting current needles.

Host Plants:

Pinus sylvestris, Scots pine, P. nigra, Austrian pine and other two and three needle pines. Scots pine seem to show variable resistance. Red pine, P. resinosa is highly susceptible in the seedling stage. Jack pine, P. bankisana, and white pine, P. strobus seem to be unaffected.

Life Cycle:

The life cycle of L. seditiosium is similar to that of Rhizosphaera kalkhoffii. The fungus overwinters on needles cast the previous season and on the previous season's growth. During the mid summer elliptical black fruiting structures develop in or just below the surface of the needle. The surface begins to bulge and split longitudinally to release spores during wet weather. The fruiting bodies,apothecia, can be readily seen with a hand lens. Spores are spread by wind and rain from midsummer to autumn and infect the current season's needles. Fruiting body maturation and time of spore release varies with host species. From late autumn to early spring of the following season, yellow spots develop on the needles which turn brown with a yellow margin. By April or May needle browning is quite conspicuous. Infected needles gradually turn reddish brown to straw coloured and drop in June and July, leaving only the current season's growth.

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Conditions Favouring Needlecast Diseases

Spore germination of both Rhizosphaera and Lophoderium is favoured under conditions of abundant moisture and cool temperatures. If temperatures are not optimal, a longer time is required for germination and the need for prolonged wetness increases. Areas which are low-lying, naturally moist, have poor air drainage or drying conditions, favour the disease.

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Control

Protecting new needles with a fungicide such as chlorothalonil will reduce the chance of infection. Avoid planting susceptible stock into areas which favour disease conditions. Improve air circulation around plants especially at the base to speed up the drying of foliage. Lower branches are often first attacked because air circulation is poor due to weeds or other plants. Collect and destroy fallen needles. Often natural foliar shed of needles in the fall can be confused with needlecast diseases. While both affect the inner needles, needles dropping due to needlecast diseases occur in early to mid summer.

For chemical control, consult OMAF Publication 383, Production Recommendations for Nursery and Landscape Plants.

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