Knowledgebase
Apple Tree Questions #926583
Asked March 23, 2026, 2:42 PM EDT
Wexford County Michigan
Expert Response
Hello Heather,
It sounds like your Red Delicious apples are showing classic early-season apple scab symptoms—small olive‑green lesions that later become corky and cause the fruit to deform. In Michigan’s cool, wet springs, scab pressure is extremely high, and Captan + Imidan alone often isn’t enough to prevent early infections.
Below is a clear breakdown of what’s happening and how to adjust your management program, based strictly on university Extension research.
What’s Causing the Deformed, Nickel‑Sized Fruit?
Apple scab is caused by the fungus Venturia inaequalis, which infects young fruit very early, from tight cluster through shortly after petal fall. When fruit is infected at this tiny stage, the lesions harden into corky patches that restrict growth, causing:
Misshapen apples
Cracking
Rough, scabby patches
Premature fruit drop
This matches your description exactly. More information at these links:
Apple Scab Fruit Fact Sheet | CALS
Why It’s Happening in Michigan
Michigan springs are typically cool and wet, which creates ideal conditions for scab infection. Spores from last year’s fallen leaves are released during every rain event from green tip through petal fall. More information at this link:
Apple Scab Fruit Fact Sheet | CALS
Even a few hours of leaf/fruit wetness at 42–75°F can trigger infection. More information at this link:
Apple Scab Fruit Fact Sheet | CALS
Why Captan + Imidan Isn’t Controlling It
A few key points:
1. Captan is a protectant only
It must be on the tissue before infection. It does not cure early infections that occurred during wet periods. More information at this link:
2. Imidan is an insecticide
It has no effect on apple scab.
3. Early-season timing is critical
Most scab infections occur before petal fall. If sprays weren’t applied tightly from green tip → petal fall, scab can establish before Captan is applied. More information at this link:
What You Can Do Now (Evidence‑Based Recommendations)
1. Strengthen your early-season fungicide program next year
University recommendations (Purdue, Cornell, MSU) emphasize:
Begin fungicide sprays at green tip.
Continue every 7–10 days until 2–3 weeks after petal fall.
Use a protectant + systemic combination during high‑risk periods.
Common home-orchard options include:
Captan (protectant)
Myclobutanil (Immunox) (systemic, curative) More information at this link:
2. Improve orchard sanitation this fall
This dramatically reduces next year’s spore load:
Apply 5% urea to fallen leaves to speed decomposition
Mulch‑mow or flail‑mow leaves after leaf drop. More information at these links:
3. Prune to open the canopy. More information at this link:
Better airflow = faster drying = fewer infections.
4. Consider resistant cultivars for future plantings
Red Delicious has some resistance but is not immune. More information at this link:
Bottom Line
Your apples are deforming because early-season apple scab infected the fruit when they were very small, and Captan alone couldn’t prevent infection during Michigan’s wet spring. Strengthening your early-season spray timing, improving leaf sanitation, and adding a systemic fungicide will greatly reduce scab pressure.
I hope this helps!
