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Foliage Diseases in Western Larch in British Columbia

By R. Garbutt

 

Introduction

Premature needle discoloration of western larch, Larix occidentalis Nutt., is a common phenomenon in south-eastern British Columbia (B. C.). The discoloration can be caused by one of a number of abiotic factors such as drought or frost, or a defoliating insect such as the larch casebearer, Coleophora laricella (Hubner), but is most often caused by a fungus dis-ease. The most common diseases affecting the foliage of western larch in B. C. are: Larch needle blightÑ caused by Hypodermella laricis Tub. (Ascomycete); and Larch needle castÑ caused by Meria laricis Vuill. (Hyphomycete).

Hypodermella laricis is native to North America, whereas M. laricis is native to Europe and was introduced to North America early in this century. Both pathogens occur in Europe on European larch, Larix decidua Mill.

Hypodermella laricis occurs on tamarack, Larix laricina Du Roi, in Ontario and the eastern United States, and on western larch in southeastern B. C., where it is a common cause of widespread premature foliar discol-oration. It has not, however, been identified from tamarack in northern British Columbia or Yukon.

Meria laricis was first identified in North America on western larch in the northwestern U. S. in 1942 (4). In 1981 it was found for the first time on west-ern larch in the Nelson and Kamloops forest regions of B. C., and on alpine larch, Larix lyallii Parl., in the Rocky Mountains of western Alberta (6). The broad distribution of infections at the time suggested that it had become established somewhat earlier. Since then, M. laricis has frequently infected the needles of western larch in native stands, sometimes in association with H. laricis, but has caused no signifi-cant damage. It has, however, long been recognized as the single most important disease of European larch in British nurseries (7). In British Columbia it has caused intermittent damage to containerized and bare-root western larch seedlings in south-ern interior nurseries since 1981. Meria laricis has not been reported on tamarack.

 

For more information, see the Foliage Diseases in Western Larch Forest Pest Leaflet in the Canadian Forest Service bookstore.