2026 Disease Update: Preventing Storage Rots and Scab

The weather around harvest can influence apple diseases that may show up in storage. This is particularly true for rots and apple scab. Although we think of apple scab as primarily an early-season problem, the pathogen can lurk and cause late-season infections under persistent wet conditions. For fungi that cause fruit rots, we have learned that fungal spores can persist throughout the season, and infections occur when favorable environmental conditions are present. Oftentimes, those conditions can occur around harvest. Unfortunately, fruit that may be harvested "clean" could show up in storage months later with small scab lesions or fruit rot. The last few weeks have seen many rain events, increasing the risk that fungicide applications will wash off and leaving wet fruit vulnerable. The following guidelines are a helpful refresher to keep fruit in the best possible shape, leading up to and during harvest.

What can growers do to minimize the threat of rots and storage scab while the fruits are still on the tree?

• Do not stretch the interval between your last spray and harvest. This is especially critical if you are planning to store any of your fruit for more than a month. If your fruit is going to a packer, chances are some varieties will be in cold storage for 2-3 months or longer.
• Preventing storage rots and storage apple scab starts in the orchard. Our research has shown the most problematic storage rots are Alternaria rot and Bull's eye rot: these infections start in the orchard.
• Although captan is an excellent preharvest fungicide for managing bitter rot and other rots, as well as scab, it can be washed off with heavy rains. A more durable fungicide should be applied as your last spray to help with any potential postharvest issues:
  • 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
• Organic options to manage fruit rots include sulfur, Oso (6.5 fl oz/A), and bacterial-based products (Serenade, Double Nickel). These options will help in the short term, especially if the fruit will be sold quickly and will not be in cold storage for an extended period.

Latent rot infections on apples during storage can contribute to a bigger problem: serving as a possible entry point for blue mold spores to cause infection and wreak havoc. Blue mold is a rot that only occurs during storage and is caused by Penicillium spp. The fungus requires a wound to cause infection. Rots can be a perfect "wound" for Penicillium spp. to gain entry. The problem with blue mold infections is that several Penicillium species, including the most ubiquitous, P. expansum, produce a mycotoxin called patulin during infection. Patulin is a regulated mycotoxin in processed products, and there are thresholds that processors must stay below. Processors will check your fruit lot; if it exceeds the patulin threshold, it will be rejected. Unfortunately, all cold storage facilities have some level of blue spores occurring. Consequently, keeping fruit protected during storage with either a preharvest fungicide or a postharvest fungicide will help limit blue mold disease and, in turn, reduce mycotoxin contamination.

For packers who want to use postharvest fungicides, there are a few options:

• Scholar (FRAC Group 12)
• Penbotec (FRAC Group 9)
• Academy (FRAC Groups 3 and 12)
• Mertect (FRAC Group 1)

There is a high level of resistance of Penicillium spp. to Mertect, so this product should not be used alone, but mixed with another fungicide.

Additional management techniques to reduce postharvest fruit rots:

• Should rotting fruit be encountered within the tree during harvest, drop the fruit to the ground. This will limit disease spread within the canopy and contamination of fruit that may be picked later.
• The more mature a fruit, the more susceptible it is to storage diseases. Harvest fruit at proper maturity.
• Bruised or wounded fruit are susceptible to postharvest fruit rots, such as blue mold and gray mold. While harvesting, handle fruit carefully when picking and transferring fruit from the bag to the bin to avoid bruising or wounding.
• Inoculum sources for rot pathogens causing disease in storage (if already not hitching a ride on the fruit) can come from plant and soil debris. Use clean bins and minimize the amount of soil and plant debris brought in on bins.
• Warm temperatures encourage pathogens to grow. Keep fruit cool after harvest, e.g., by keeping bins in the shade.
• If delivering to a packinghouse, minimize the time between harvest and fruit delivery.

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.