Aspen and poplar shoot blight, Venturia macularis

Fig. 376  V. populina on hybrid poplar. Note the blackened dead tissue forming a sheperd's crook.	Fig. 377 Defoliation damage of aspen caused by Venturia spp.

Distribution:  Widely distributed throughout the range of its hosts in B.C.  Venturia macularis is especially severe in northern B.C.

TREE SPECIES ATTACKED:  Venturia macularis attacks primarily trembling aspen. Venturia populina attacks balsam poplar, hybrid poplars, and black cottonwood.

WHAT TO LOOK FOR: Blacken and wilted new tissues that resemble a shepherd's crook. Masses of olive-green spores on blackened dead tissue.

SIGNS & SYMPTOMS: These fungi overwinter in sexual and asexual structures found on dead shoots, leaves, and blighted twigs. Spores are dispersed in the spring via wind and rain to infect newly formed shoots and leaves. The fungus first appears as black leaf spots. The spots will continue to spread down the leaves into succulent branchlets. The infected new shoots and leaves will turn black and wilt, resembling a shepherd's crook. A velvety mat of olive-green conidia (spores) are produced on the blackened, dead tissue. These spores are rain-dispersed and continue the infection on new leaves. Wet springs and summers are optimum conditions for infection.

DAMAGE: Crowns are stunted and deformed when Venturia infections occur over successive years. During wet moist springs, V. macularis can kill most shoots in aspen stands regenerated by sprouting. V. populina has had a great impact on intensively managed hybrid poplar plantations. In damp, coastal hybrid plantations, cankers can develop and dieback areas are prone to breakage. Susceptible hybrid clones have been replaced with more resistant clones to reduce the impact of V. populina. Overall, wetter climates have the greatest infection rates and impact.

SIMILAR DAMAGE: V. populina and V. macularis produce the same symptoms but on different tree species. Microscopically, they can be distinguished by their different-sized spores. Leaf spots caused by purple-brown leaf spot of aspen (Pallaccia borealis) are similar to those caused by V. macularis. However, P. borealis does not cause shoot dieback. 

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 04, 2002