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Scab - Venturia inaequalis

Damage

Scab lesions (diseased areas) are often first noticed on leaves, where they most commonly occur on the upper leaf surface. Fruits are also very susceptible to infection. Lesions on both leaves and fruits are roughly circular with feathery edges, and have an olive green to black color. They can be as small as the size of a pinhead or as large a 1/2 inch in diameter. When the disease is severe, lesions can merge and cover a large portion of the leaf or fruit surface. Defoliation of the tree often follows.

Cultural Controls

Plant disease-resistant cultivars. Remove and destroy all fallen, infected leaves.

Remarks

Apply 4 to 5 times at 10-day intervals, beginning at bud break.

Chemical Controls

Azoxystrobin

Signal Word: Caution
Pesticide Class: Systemic-Upward only

Boscalid+Pyraclostrobin

Signal Word: Caution
Pesticide Class: Local Protectant

Chlorothalonil

Signal Word: Warning
Pesticide Class: Protectant

Chlorothalonil+Thiophanate methyl

Signal Word: Danger
Pesticide Class: Protectant, Systemic-Upward only

Copper hydroxide

Signal Word: Danger
Pesticide Class: Protectant

Iprodione+Thiophanate-methyl

Signal Word: Caution
Pesticide Class: Local Protectant, Systemic-upward only

Kresoxim-methyl

Signal Word: Caution
Pesticide Class: Local protectant

Mancozeb

Signal Word: Caution
Pesticide Class: Protectant

Mancozeb+Thiophanate-methyl

Signal Word: Caution
Pesticide Class: Protectant, systemic-upward only

Myclobutanil

Signal Word: Warning
Pesticide Class: Systemic-upward only

Neem oil

Signal Word: Caution
Pesticide Class: Protectant

Phosphorous acid

Signal Word: Caution
Pesticide Class: Systemic

Polyoxin-D Zinc Salt

Signal Word: Caution
Pesticide Class: Local protectant

Propiconazole

Signal Word: Warning
Pesticide Class: Systemic-upward only

Pyraclostrobin

Signal Word: Caution
Pesticide Class: Local protectant

Thiophanate-methyl

Signal Word: Caution
Pesticide Class: Systemic-upward only

Trifloxystrobin

Signal Word: Caution
Pesticide Class: Local protectant

Trifloxystrobin+Triadimefon

Signal Word: Caution
Pesticide Class: Local protectant, Systemic-upward only

Triflumizole

Signal Word: Caution
Pesticide Class: Systemic-upward only

Locations Affected

fruit, leaves

Plant Environment

outdoors

Scouting Season:

May - Early , May - Mid , May - Late , June - Early , June - Mid , June - Late , July - Early , July - Mid , July - Late , August - Early , August - Mid , August - Late

Plants Affected

• Cotoneaster - Cotoneaster
• Fraxinus - Ash
• Malus - Crabapple

Photos

Close up of apple scab on leaf.

Apple scab on apple leaves.

Crabapples defoliated by apple scab.

Apple scab on young fruit.

Apple scab on young fruit and leaf.

Apple scab on mature fruit.

Fruit infected with apple scab still on the branch.