2026 Disease Update: Apple Scab and Fire Blight Risk April 18 - 19

No rest for the weary this week! As we approach the weekend, the forecast indicates rain for many areas beginning in the evening of April 18 and continuing through April 19. For those experiencing bloom through petal fall, this will be a significant apple scab and severe fire blight event. Bloom through petal fall is when the maximum number of apple scab spores are mature in overwintering leaves and are ready to be released. Combined with the warm temperatures, only 6 hours of leaf wetness will be necessary for infection. This will be an important scab infection event should the forecast come to fruition. Unfortunately, with bloom comes the risk of fire blight, and the current temperatures have significantly increased the risk for infection if a rain event occurs. With warm weather persisting through Saturday, the rain will trigger an infection event on April 18. Growers must ensure their orchards are covered before the forecasted wetting event this weekend.

Fire blight

Even if growers sprayed on April 15 or 16 to protect against fire blight, protection is still necessary on or before April 18 because temperatures have been so high, and additional blossoms have opened. Given the severity of the conditions many have experienced during bloom this week, growers are strongly encouraged to include prohexadione calcium (ProCa; Kudos, Apogee) in their streptomycin spray to help mitigate potential shoot blight in the coming weeks. ProCa will harden shoots, making them less susceptible to fire blight. Additional ProCa applications will be necessary, as the product's effects take 10-14 days to kick in. It's not a matter of if fire blight will occur, but when this year.  

For more information about protecting apple trees from fire blight, please refer to the 2026 Disease Update from April 13, 2026.

Managing fungal diseases on apple bloom through petal fall

Apple scab, rust, powdery mildew, and Marssonina blotch are of concern during this time. Marssonina blotch management should begin at petal fall. For disease management from bloom through petal fall, growers are strongly encouraged to use complete sprays rather than ARM (alternate row middle), especially if frequent rain events favor extended wetness. During this period, it is best to use FRAC Group 7, 7 + 9, or 7 + 3 fungicides when tank-mixing with a rainfast mancozeb (3 lb/A). 

• Aprovia (FRAC Group 7)
• Excalia (FRAC Group 7)
• Fontelis (FRAC Group 7)
• Kenja (FRAC Group 7)
• Miravis (FRAC Group 7)
• Tesaris (FRAC Group 7)
• Luna Tranquility (FRAC Groups 7 + 9)
• Luna Flex (FRAC Groups 7 + 3)

 When necessary, rotate FRAC Group 7 fungicides with the following:

• Cevya (FRAC Group 3)
• Indar (FRAC Group 3)
• Inspire Super (FRAC Groups 3 + 9)
• Procure (FRAC Group 3)
• Scala (FRAC Group 9)
• Vangard (FRAC Group 9)
• Axios (FRAC Group 52)

Do not use products with FRAC Group 11 during this period (Cabrio, Flint Extra, Luna Sensation, Merivon, Pristine). Please save these products for summer rot control during cover sprays and your last preharvest spray.

Managing fungal diseases on apple through pink

Growers in northern Pennsylvania may be a bit behind this week compared to those in the southern part of the state. When disease conditions are favorable for apple scab through pink, consider using fungicides from FRAC Groups 3 when tank mixing with a rainfast mancozeb (3 lb/A); save FRAC Group 7 fungicides for bloom through petal fall:

• Cevya (FRAC Group 3)
• Indar (FRAC Group 3)
• Inspire Super (FRAC Groups 3 + 9)
• Procure (FRAC Group 3)
• Scala (FRAC Group 9)
• Vangard (FRAC Group 9)

For organic control, options include:

• Micronized sulfur (8 – 10 lb/A)
• Potassium bicarbonate (3 lb/A)
• EcoSwing (2 pt/A)
• For those using low-risk programs, sulfur and potassium bicarbonate can both control powdery mildew and scab.

Stone fruit disease management

For disease management during bloom through petal fall on stone fruit, please refer to the 2026 Disease Update from April 7, 2026. 

Additional Resources

• Dr. Tree Fruit and Don Podcast  
• Penn State 2026 – 2027 Tree Fruit Production Guide 

For commercial fruit growers, please note: When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one's own orchard. To support management decisions (especially during infection events), growers can use the NEWA website, which has weather stations across Pennsylvania.  Before applying chemical products, be sure to comply with current use regulations and read the product label. Product information can easily be obtained from CDMS, Agrian, or Greenbook.