Apple Scab: Control Methods and Specific Fungicides
What does apple scab disease look like? What is the ecology behind its occurrence? What control methods are there?
Symptoms: It damages leaves and fruit. Initially, olive-colored irregular round spots appear on the underside of leaves, later turning gray-black, sometimes with a black metallic sheen, and the leaf tissue is gradually destroyed. Generally, affected leaves become smaller, deformed, slightly curled, and drop prematurely. On fruit, the spots are round; in the early stage they bear a gray-green fuzzy growth, and the black material consists of conidia. Later the spots turn dark brown, the skin cracks and becomes suberized, taking on a scab-like appearance, and the fruit becomes deformed. Fruit infected early is prone to dropping.
Disease ecology: At temperatures of 15-20°C with continuous rainfall, the disease is severe. The sexual stage of this fungus has not yet been found in Taiwan, China; it may overwinter as mycelium latent in buds, or overwinter in dead branches and fallen leaves. The conidia produced on leaves (olive-green and fuzzy in appearance) are the main organs of transmission and infection and can cause repeated infections.
Control methods:
40% Myclobutanil wettable powder
Begin spraying at the early stage of disease onset, spraying once every ten days until mid-July. Stop application 6 days before harvest.
30% Difenoconazole wettable powder
Begin application at the early stage of disease onset, spraying once every 10 days for four to six consecutive applications. 1. In trials of this fungicide, the spreader-sticker Rabiden-SS was added at 3000 times dilution. 2. Stop application 12 days before harvest.
65% Dodine wettable powder:
1. Apply once a week after bud break.
2. After petal fall, apply once every 10 days until mid-August.
1. Add spreader-sticker at 3000 times dilution to the spray solution to prevent rain wash-off and reduced efficacy.
2. If there is continuous overcast rain, the number of applications should be increased.
3. Do not apply during the flowering period.
Stop application 4 days before harvest.
70% Methyl zineb wettable powder
Stop application 4 days before harvest.
70% Methyl thiophanate wettable powder
1. Apply once a week after bud break.
2. After petal fall, apply once every 10 days until mid-August.
1. Add adhesive at 3000 times dilution to the spray solution to prevent rain wash-off and reduced efficacy.
2. If there is continuous overcast rain, the number of applications should be increased.
3. Do not apply during the flowering period.
4. To avoid the fungus developing resistance to the fungicide, it should be used alternately with other fungicides.
50% Benomyl wettable powder
1. Apply once a week after bud break.
2. After petal fall, apply once every 10 days until mid-August.
50% Benomyl wettable powder mixed with 7E Sunspray oil
Add 25 grams + 250 mL per 100 liters of water, 4,000, mixed and applied once every 10 days
1. Add adhesive at 3000 times dilution to the spray solution to prevent rain wash-off and reduced efficacy.
2. If there is continuous overcast rain, the number of applications should be increased.
3. Do not apply during the flowering period.
4. To avoid the fungus developing resistance to the fungicide, it should be used alternately with other fungicides.
50% Benomyl wettable powder mixed with 7E Sunspray oil
Add 25 grams + 250 mL per 100 liters of water, 2000 mixed with 400, applied once every 20 days
1. Add adhesive at 3000 times dilution to the spray solution to prevent rain wash-off and reduced efficacy.
2. If there is continuous overcast rain, the number of applications should be increased.
3. Do not apply during the flowering period.
4. To avoid the fungus developing resistance to the fungicide, it should be used alternately with other fungicides.
50% Benomyl wettable powder mixed with 30% Guoning solution
Add 25 grams + 125 mL per 100 liters of water, 4000 mixed with 800, applied once every 10 days
70% Methyl thiophanate wettable powder mixed with 30% Guoning solution
Add 33.3 grams + 125 mL per 100 liters of water, 3000 mixed with 800, applied once every 10 days
11.76% Fenarimol emulsion (Fenarimol)
Begin application at the early stage of disease onset, applying once every 10 days for eight consecutive applications.
1. In trials of this fungicide, "Quanto" at 1000 times dilution or "Chulaitong" at 2000 times dilution was added.
2. Stop application 5 days before harvest.
12% Fenarimol wettable powder
Begin application at the early stage of disease onset, applying once every 10 days for eight consecutive applications.