| | Leaf & Shoot Blight of Aspen (Venturia macularis); Septoria Leaf Spot (Mycosphaerella populicola); Marsonina Leaf Spot of Aspen (Marssonina populi)
Crops Affected: various aspens and poplars, depending on pathogen species
Disease Cycle:
- Fungal pathogens
- Spores are generally produced in the leaf litter, or on twig lesions (depending on pathogen), spreading to infect new leaves
- Continuous wet weather in spring, and warm/moist conditions in summer, can result in the production of spores and rapid spread
- Secondary disease development is more common in some diseases (e.g. Marssonina), regardless of conditions, although rate of spread is linked to presence of conditions
Symptoms
Venturia
- Angular black spots form on host foliage, with spots growing and merging to cover the entire leaf/shoot, resulting in wilting and necrosis of the entire structure
- Affected parts continue to elongate, producing a drooping “shepherd’s crook” symptom
- Can kill a significant number of terminal shoots, in severe situations
Mycosphaerella
- Initially starts as small, circular to angular, white, grayish, tan, brown, or purplish spots with a dark border
- Spots may coalesce to form blotches
- Dark specks (pycnidia – fruiting structures) are scattered in older lesions
Marssonina
- Small, brownish spots appear on infected leaves from as early as the end of leaf expansion, through July and August
- Spots enlarge, turn brownish black, and often have a yellow margin and a white center
- Spots may coalesce to form vein-limited, necrotic blotches
- Infected leaves may fall prematurely, particularly when infection occurs at/on/near the leaf petiole
- Stands may appear thin, due to loss of leaves
| | |
Venturia leaf blight on aspen | Septoria leaf spot on poplar
| Marssonina blight on aspen leaves
|
Photo by: tidcf.nrcan.gc.ca | Photo by: tidcf.nrcan.gc.ca | Photo by: William Jacobi, Colorado State University, Bugwood.org |
Conditions Favouring Development:
- Generally favoured by cool, wet weather in spring
- Warm, moist conditions in summer can result in further spread
Management:
- Remove and destroy leaves that drop, and/or twig/branches or other infected material, to reduce inoculum levels and reduce spread
- Plant resistant species or clones, if available
- Ensure that there is adequate spacing between plants, to improve air circulation and reduce humidity
- Fungicides (applied in spring) are largely impractical in the vast majority of situations
|
|