Environment Canada is forecasting a 40-60% chance of precipitation for much of this week, its raining in the southwest this morning. There are several diseases that will be active this week on Rosaceous plants such as apple, pear and serviceberry…..
Mid-spring diseases will be sporulating, such as Fireblight, Apple scab and Gymnosporangium rusts (e.g. cedar-apple rust). Fungicide applications during bud break and leaf emergence BEFORE precipitation events are the best way to help protect new growth on Rosaceous hosts (Malus, Pyrus, Amelanchier) and reduce the incidence of disease.
Look for bleeding cankers or oozing on bark and twigs on apple and pear as a sign of the active stage of this disease now:
Where leaf buds are still in the green tip to 1/2″ green stage, (e.g. east of Toronto), copper sprays may still be effective at killing any bacteria that land on leaf and twig tissue. Do not use copper after 1/2″ green bud, it may be phytotoxic to leaves.
The window of infection starts once FLOWERS ARE BLOOMING. Most fireblight infections enter the delicate flower tissue. Protect flowers and emerging leaves with bactericidal products such as Kasumin (Grp 24) and Streptomycin (Grp 25) during bloom. For suppression of fireblgiht in the landscape with Class 11 biological fungicides, Blightban C9-1 and Bloomtime can be used during bloom of apple and pear.
CHECK IT OUT! Prediction models for Fireblight Activity in southern Ontario May 9-15 can be found here:
2) APPLE SCAB:
Apple scab causes diffuse-looking spots along leaf veins and often leads to premature leaf drop in June. Where leaf buds are still in the green tip-1/2″ green stage (e.g. east/north of Toronto), copper sprays may be still be effective at killing any spores that land on the leaf tissue. Note: copper should be avoided beyond 1/2″ green tip stage (as leaves are emerging) to avoid potential phytoxicity issues.
Where ornamental crabapples are further along in leaf emergence, try fungicides such as Nova (Grp 3, rotate with other fungicides to avoid resistance), Pristine (Grp 7, 11), Compass (Grp 11), Captan (Grp M) and Manzate (Grp M) . For supression of apple scab in the landscape with Class 11 fungicides, Serenade Max (Bacilus subtilis) and sulphur can be used to help protect emerging foliage from this disease.
3) GYMNOSPORAGIUM RUSTS:
There are several species of Gymnosporangium rusts that sporulate on the Juniper host in warm, wet conditions in May. Examples include cedar-apple rust, cedar-hawthorn rust, cedar-quince rust and pear trellis rust. Gymnosporangium rusts produce bright orange, gelatinous sporulation masses from perennial galls or directly on twigs and stems of Juniper.
These sporulating masses send spores that will infect the alternate host, the Rosaceous plants such as apple, pear, serviceberry etc. to cause bright orange lesions on leaves in summer.
Monitor for bright orange sporulation on Juniper during warm, wet weather and protect Rosaceous plants with fungicides such as Nova (Grp 3), Pristine (Grp 7, 11), Daconil (Grp M) and Manzate (Grp M).