Cause The fungi Ophiognomonia intermedia (formerly Discula betulina) and Gloeosporium betulae (formerly Marssonina betulae) cause anthracnose. Generally, these fungi are not severe enough in the landscape to warrant fungicide application but can be an issue on young seedlings in the nursery. These pathogens overwinter on blighted twigs and petioles. Spore spread and infection occur during wet weather in spring. Young, developing shoots and leaves are most susceptible.
Symptoms Large reddish-brown spots that can run together to form larger blotches. Leaf blotches tend to have indefinite margins, and the remaining leaf tissue turns yellow. Spore-producing structures of the fungi (acervuli) are produced under the cuticle on the upper leaf surface. Other leaf symptoms range from small distinct spots to raised or puckered areas. Severe anthracnose can cause premature defoliation and dieback of young birch shoots.
When inoculated, Gloeosporium betulae caused discrete lesions on new shoots, which often girdled, causing dieback of the leading shoot. The development of secondary sunken cankers on the main stem also occurred, which were usually centered around a dead sideshoot. Cankers on the main stems expanded during subsequent growing and dormant seasons, and often coalesced, girdling stems and causing the death of some seedlings.
Cultural control
- Rake up and dispose of fallen leaves and plant debris.
- Space plants for better air circulation and drying after rain.
Chemical control Fungicide sprays during budbreak and leaf expansion can lessen disease severity.
- Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
- Compass Fungicide at 2 to 4 oz/100 gal water. Do not use organosilicate additives. Group 11 fungicide. 12-hr reentry.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide. 24-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Group 3 fungicide. 24-hr reentry.
- Myclotect at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Group 3 fungicide. 24-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
- Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Green, S. and MacAskill, G. A. 2007. Pathogenicity of Marssonina betulae and other fungi on birch. Plant pathology, 56:242-250.