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Beginner

Scientific Name: Sphaerulini rubi and Septoria rubi

Identification

• Raspberry leaf spot, Sphaerulini rubi, occurs on raspberries only.
• Septoria leaf spot, Septoria rubi, affects only erect and trailing blackberries.
• Both diseases commonly known as “septoria leaf spot”, but the two diseases do not cross-infect under field conditions.
• Raspberry leaf spot causes greenish-black spots on the upper surface of new leaves. Spots progress to a whitish-grey with a distinct margin and sometimes a shot-hole in the centre.
• Septoria leaf spot causes ‘frog-eye’-like lesions with a black to purple outer margin and a whitish-grey centre on the upper leaf surface. 
• Severe cases can lead to premature defoliation by the end of summer or early fall.

Often Confused With
Anthracnose

Period of Activity
The fungus overwinters on old leaves and canes. In spring, spores are spread to new leaf and cane tissue by splashing, wind-driven rain. Young rapidly expanding leaves are infected in spring and early summer, infection continues throughout the summer.

Scouting Notes
Look for the characteristic greenish-black or whitish-grey leaf spots on the upper surface of young leaves. Pay close attention to susceptible varieties (eg. Reveille, Canby) and areas with a history of this disease. Expect more problems in plantings which are not routinely sprayed for other diseases. Rainy weather in spring and summer can spread the spores of the fungal pathogens and expose more plants to the disease. Watch for symptoms after periods of heavy rain.

Thresholds
None established.  

 

Advanced

Scientific Name: Sphaerulini rubi and Septoria rubi

Identification

• Septoria leaf spot is caused by Septoria rubi. It affects only erect and trailing blackberries.
• Raspberry leaf spot is caused by the fungal pathogen Sphaerulini rubi and occurs on raspberries only.

It is generally accepted that these two diseases do not cross-infect under field conditions.

• Septoria leaf spot on blackberries causes ‘frog-eye’-like lesions. These are circular spots about 3 to 4 mm in diameter with a black to purple outer margin and a whitish-grey centre on the upper leaf surface.
•  Raspberry leaf spot causes spots to develop on the upper surface of new raspberry leaves. These spots are greenish-black with well-defined margins, usually 1 to 2 mm but up to 6 mm in diameter. Later in the season, their colour changes to whitish-grey and in some cases affected leaf tissue drops out, creating a shot-hole effect.

Severe cases of these diseases can lead to premature defoliation of affected plants by the end of summer or early fall. This can lead to weakened plants and increased risk of winter injury.

Often Confused With

Anthracnose
The fungus which causes anthracnose on canes can also cause leaf spot. In the case of anthracnose, leaf spots are smaller, less circular and develop earlier in the season. Leaf spots caused by anthracnose are usually found when there are symptoms of anthracnose on canes and petioles.  Check leaf spots with a 10 X hand lens for tiny, flattened, black pycnidia in the whitish-grey centre. The presence of pycnidia is diagnostic for raspberry or septoria leaf spot.

Biology
Both pathogensoverwinter as mycelium and immature pycnidia on old canes and leaves. In spring, conidia and ascospores are spread to new leaves and canes by splashing, wind-driven rain. The spores then germinate in a film of moisture before penetrating the leaf. Once a leaf is infected, spots develop on the upper leaf surface.  Elongated lesions can develop on canes and petioles. As the leaf spot ages, tiny, flattened, brown to black pycnidia, visible with a 10X hand lens, grow in the whitish-grey centre. The pycnidia give rise to new conidia. If the season is wet, these conidia spread to new plant tissue and cause secondary infections for the remainder of the growing season. In the fall, overwintering structures, pycnidia and perithecia, form on leaves and canes.  

Period of Activity
The fungus overwinters on old leaves and canes. Young rapidly expanding leaves are infected. Infections occur throughout the summer especially during periods of splashing rain and wet weather.

Scouting Notes
Look for the characteristic greenish-black or whitish-grey leaf spots on the upper surface of young leaves. Pay close attention to susceptible varieties (eg. Reveille, Canby) and areas with a history of this disease. Expect more problems in plantings which are not routinely sprayed for other diseases. Rainy weather in spring and summer can spread the spores of the fungal pathogens and expose more plants to the disease. Watch for symptoms after periods of heavy rain.

Thresholds
None established.  

Management Notes

• In order to prevent the spread of fungal spores, it is important to employ good canopy drying techniques by promoting air circulation. Ensure that plants are supported on a trellis. Thin out canes and maintain an appropriate cane density.
• Keep rows narrow and weeds controlled to improve drying of the plants.
• Start out with clean, disease-free stock.
• Prune out old fruiting canes. Remove dead, damaged or infected plant material to reduce overwintering inoculum.
• Broad-spectrum fungicides applied to control botrytis grey mould, generally help to control leaf spot.
• Some varieties such as Reveille are particularly susceptible.