2026 Disease Update: Apple Scab Infection Forecasted for April 1 - 2

The whiplash of winter and summer temperatures continues for the region as we close out March and start April. The warm weather from March 8 – 12 prompted many trees in the southern half of Pennsylvania to break dormancy. In this region, green tip occurred from March 17 through 22, depending on the variety. Once apple trees break dormancy, this means "go time" for the apple scab spores existing in last season's overwintering leaves. The rain on March 26 – 27 triggered an apple scab infection event, and folks were protected from it if they had applied a dormant copper spray to their apple trees. The region is in store for ideal weather in the coming week, which may push more apple orchards throughout Pennsylvania to green and could trigger apple scab infections on apple trees with green tissue. The current forecast suggests that apple scab infections will be favored on April 1 – 2, and growers should keep an eye on April 3 – 5, since there is an over 60% chance of rain (as of Sunday, March 29, 2026). It is important to closely monitor your location. General tips for disease management during this time are discussed. For those who have not applied dormant copper sprays, please refer to the March 2, 2026 Disease Update.

Disease management through half-inch green tip

Management options:

• If you have recently applied a dormant copper application, this will protect your apple trees through this apple scab infection period.
• Rainfast mancozeb alone at 3 lb/A
• Rainfast mancozeb 3 lb/A + Syllit (FRAC Group U12; 1.5 pt/A)
• Rainfast mancozeb 3 lb/A + Micronized sulfur (6 – 10 lb/A)
• Organic options: Potassium bicarbonate (3 lb/A) or sulfur

Disease management during tight cluster

With the temperature forecast to be 70 – 80°F this week, bud development may advance quickly. Consider the following fungicides to tank mix with rainfast mancozeb (3 lb/A):

• Axios (FRAC Group 52; 3 fl oz)
• Cevya (FRAC Group 3; 5 fl oz/A)
• Indar (FRAC Group 3; 8 fl oz/A)
• Inspire Super (FRAC Groups 3 + 9; 12 fl oz/A)
• Procure (FRAC Group 3; 16 fl oz/A)
• Scala (FRAC Group 9; 5 – 10 fl oz/A)
• Vangard (FRAC Group 9; 5 oz/A)

Growers are highly encouraged not to use the FRAC Group 7 fungicides during this time; these fungicides are best saved for peak apple scab and Marssonina blotch pressure, which is from late pink through petal fall for apple scab, and petal fall through the second cover for Marssonina blotch.

 As a reminder, tight cluster begins powdery mildew control. Powdery mildew infections occur when dry days are 50 - 77°F with humidity >90%. Beware of multiple days in a row of dry weather. If conditions are dry (particularly between wetting events), focus on managing powdery mildew by tank mixing a rainfast mancozeb with any of the following:

• Axios (FRAC Group 52; 3 fl oz)
• Cevya (FRAC Group 3; 5 fl oz/A)
• Rally (FRAC Group 3; 10 oz/A) or Sonoma (FRAC Group 3; 4.8 fl oz/A)
• Rhyme (FRAC Group 3; 6.5 fl oz/A)
• Procure (FRAC Group 3; 16 fl oz/A)
• Torino (FRAC Group U6; 6.8 fl oz/A)
• Gatten (FRAC Group U13; 6 – 8 fl oz/A)
• Micronized sulfur (6 – 10 lb/A)

For organic control, options include:

• Micronized sulfur (6 – 10 lb/A)
• Potassium bicarbonate (3 lb/A)
• EcoSwing (2 pt/A)

Although dry weather favors low apple scab pressure, it does not favor low powdery mildew pressure. Some strong powdery mildew products are not as effective against scab; however, tank mixing with a broad-spectrum fungicide (i.e. mancozeb) will keep scab in check when we do have rain events in the middle of dry stretches. For those using low-risk programs, sulfur and potassium bicarbonate can both control powdery mildew and scab.

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 assist with management decisions (especially during infection events), growers can use the NEWA website, which has weather stations all over 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.