Post-Harvest Disease Control in Apples

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The weather is colder now and apples have been harvested. Fall and winter is the time to be thinking about orchard post-harvest best practices including disease control in apples. The good news is that diseases can be managed. Apple growers and packers can implement specific measures to minimise disease risks to apples pre and post-harvest.  

Firstly, let’s look at some of the diseases that may occur in your apples, post-harvest, and how to identify them. Though we may not see the visual symptoms of a disease in the field, some diseases may be initiated in the orchard. There are several diseases that can cause losses in apples. In this blog we will address two common diseases seen post-harvest.

Gray mold (Botrytis cinerea): Although Botrytis, like many other pathogens can easily infect fruit through splits, wounds or punctures occurring at harvest, gray mold infections generally start earlier in the orchard. The fungus can infect flowers at bloom and fruits during the growing season. Infections remain latent (dormant) until fruit have been in storage for several months, and then develop symptoms. Symptoms include a spongy texture, with a light to dark brown colour. The decayed tissue cannot be separated from healthy tissue. In advanced stages fluffy white-gray mycelia can be seen. Common inoculum sources include apple mummies on trees and dead leaves. More information and pictures of grey mold can be found here.

Gray mold on a Gala apple. Image credit/source: Washington State University.
Gray mold, on a Granny Smith apple, originating from a side would infection. Image credit/source: Washington State University.

Blue mold (Penicillium expansum & spp.): This is caused by a wound to the apple’s skin, creating a point of entry for the fungus. We often see blue mold infections associated with stem punctures. Blue mold symptoms include round lesions in a light beige to darker brown colour. The lesions have a soft, watery texture, and are easily ‘scooped’ away from the healthy fruit. Blue to green coloured spores are seen at more advanced stages, hence the name Blue mold. Although the growth of Penicillium spp. is limited in cold storage, the fungus can grow at temperatures as low as -3ºC. Orchard sanitation to remove decayed fruit and organic debris on the orchard floor helps reduce inoculum levels the orchard.  Good harvest and handling practices designed  to minimize fruit punctures and bruises are critical to minimize blue mold infections. Common inoculum sources include bins, rooms, flume water, soil. More information and pictures of blue mold can be found here.

Grey mold on a Granny Smith apple, originating from a side wound infection. Image credit/source: Washington State University.
Blue mold evident on a Fuji apple. Image credit/source: Washington State University.

Disease Management

When it comes to disease management in apples, preventative methods such as sanitation will greatly minimize the risk.  chemical methods that can be applied if the fungus has taken hold.

Integrated Pest Management (IPM) includes different practices to minimize economic damages. Cultural practices that can be implemented throughout the growing season include:

  • Apply needed nutrients to maximize tree health
  • Closely monitor your trees for pest and disease issues
  • Apply a pre-harvest fungicide 
  • Harvest apples at ideal regular or long term storage maturity to avoid splitting and cracking. (consult Packer)
  • Practice proper picking and handling harvest techniques to avoid stem punctures and excessive bruising. Growers Supply carries Apple Stem Clippers. Click here to order yours.
  • Practice good sanitation, use clean bins and keep all tools clean.

Scholar® 230SC fungicide Group 12 provides post-harvest protection from several storage rot diseases. Scholar can be used as a post-harvest drench on pome fruit to control the development of Blue Mold and Gray Mold as well as other diseases. It is a non-systemic, surface fungicide that comes in a 1L Jug. More information and the full product label can be found here.

These few simple practices can really make a difference in the quality and longevity of your fruit. As always, we’re here to support. Please reach out to our grower’s support team with your questions.

Blog references and further reading: