Apple Scab
Class: Fungi
Common Name
Apple scab
Scientific name
Venturia inaequalis
Potential Hosts
Apples
Who am I?
Apple scab is a fungal disease of great agricultural importance and worldwide dispersion. Apple scab remains dormant on the plant debris of previous seasons. Infestations can occur anytime between the initial phase of fruit formation to the time when fruits are picked. A apple scab outbreak is triggered with wetting events and disperses and reproduces during through splashing water. Green to black circular spots with a dusty-like texture appear on leaves and fruits. If not properly treated, crops exhibit decreased photosynthesis, fruit tissue damage, and fruit deformation.
Control measures
Cultural
Apple scabs remains dormant on the plant debris of previous seasons that are found on the ground. Therefore, simple sanitation measures are important for lowering the risk of an outbreak.
Conventional (chemical)
Well-timed preventive spraying applications are important, especially in apple varieties in which bud breaking begins in a rainy period.
It is common to have a minimum of two preventive spraying applications from bud break until weather conditions become stable. It is suggested that additional treatments should be applied every 8-10 days in varieties that the buds break in rainy periods.
The following fungicides are still in use in one or more parts of the world: tebuconazole, trifloxystrobin, cyproconazole, and azoxystrobin (applied only for when (and if) apple scab symptoms are clearly present), and captan, dithianon, bromuconazole, mancozeb, and sifenazolenoco.
Do not use products based on the same active ingredient in consecutive treatments, as this may induce fungi resistance to that specific ingredient used.
Caution and careful notice should be taken when using any plant protection products (insecticides, fungicides, and herbicides). It is the grower’s sole responsibility to keep track of the legal uses and permissions with respect to the laws in their country and destination markets. Always read the instructions written on labels, and in a case of contradiction, work in accordance to the product label. Keep in mind that information written on the label usually applies to local markets. Pest control products intended for organic farming are generally considered to be less effective in comparison to conventional products. When dealing with organic, biologic, and to some extent a small number of conventional chemical products, a complete eradication of a pest or disease will often require several iterations of a specific treatment or combination of treatments.