2026 Disease Update: Protect Apples Before Multi-Day Rain Forecast

Growers should review their spray records to determine when the last fungicide application was made, particularly in blocks containing late-season varieties. The forecast calls for rain throughout much of next week (September 20-23), and these wet conditions, coupled with moderate temperatures, will create an ideal environment for infection by pathogens responsible for fruit rots and storage scab. Growers are strongly encouraged to apply a fungicide to any apple blocks that have not yet been harvested before this weather system arrives.

Pathogen pressure is already high in many orchards, as evidenced by the substantial incidence of apple scab, fruit rots, and Marssonina blotch observed on leaves and fruit in plant pathology research orchards at the Penn State Fruit Research and Extension Center. As a reminder, growers should remain vigilant during the harvest season, maintain fungicide coverage on fruit throughout harvest, and make the final fungicide application as close to harvest as label restrictions allow.

Although captan remains an option many growers may choose, the extended wet period in the forecast warrants adding a more rainfast, longer-lasting fungicide. Growers are encouraged to tank-mix captan with one of the following products:

• Merivon (FRAC Groups 7 + 11; 0-day PHI)
• Luna Sensation (FRAC Groups 7 + 11; 14-day PHI)
• Flint Extra (FRAC Group 11; 14-day PHI)
• Cabrio (FRAC Group 11; 0-day PHI)
• Thiophanate-methyl (FRAC Group 1; 1-day PHI)

Thiophanate-methyl generally provides less effective control of fruit rots than the FRAC Group 11 fungicides. Therefore, it is strongly recommended that thiophanate-methyl always be tank-mixed with captan to improve disease control and help manage resistance. For organic production systems, options for fruit rot management include micronized sulfur (10 lb/A), Oso (6.5 fl oz/A), and biological products such as Serenade and Double Nickel.

As always, consult product labels for specific use directions, rates, preharvest intervals, and resistance management guidelines.

For additional information on controlling disease during the harvest period and preventing postharvest rots and storage scab, refer to the August 12, 2026, Disease Update. 

For 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.