As fruits make their way into storage, presses, markets, and the hands of consumers, a new set of tasks must take place on the farm to ensure healthy vines and fruit trees are well prepared for winter. Of these tasks, disease management is a top priority despite the absence of fruits in the canopy. Post-harvest disease management practices can help reduce the threat of diseases next season. With the fall season approaching there are several important considerations for your apple trees and grapevines to help support a successful season next year.

Apple orchards

• Fallen leaves should be burned, buried, or mowed to shred and increase the rate of decay. This helps reduce apple scab inoculum that overwinters in fallen leaves and can serve as a source of inoculum the next season.
• The application of a 5% solution of agricultural grade urea (46-0-0) to the orchard floor (40 lb. per acre in 100 gal. of water) can help reduce apple scab inoculum by providing nitrogen to help microorganisms decompose leaves.
  • Urea can be applied to leaf litter in late autumn and/or early spring.
  • Note: Urea provides nitrogen so adjust your fertilization program appropriately.
• Clean up fallen fruit from the orchard floor (Figure 1) and diseased and/or decaying fruit (mummies) in the tree canopy. Both sources of fruit can harbor fungal spores that can overwinter and initiate new infections next season.
• Dormancy is a great time to reflect on what worked well and what could use improvements in your disease management approaches. Sanitation practices made now in the orchard will help contribute to reduced disease pressure in the following season and make your fungicide and bactericide applications that much more effective.
• Winter pruning is an important time to remove fire blight “hold over” cankers to reduce the amount of primary inoculum for the next season. Fire blight strikes can also be colonized by various canker fungi and serve as an inoculum source for fungal pathogens, so this sanitation step is very important.
• Additionally, removal of dead branches can help prevent colonization of opportunistic fungal pathogens that overwinter on dead branches and supply inoculum in subsequent seasons.
• Piles of pruning’s should be removed from the perimeter of the orchard or burned, as they are an important source of inoculum for several diseases including black rot, white rot, and bitter rot.

Vineyards

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• Scout for powdery mildew (Figure 2) and downy mildew (Figure 3) infections; these diseases can appear late in the season and reduce photosynthesis, defoliate vines, and increase the risk for winter injury. If these infections were not managed during the growing season, they may continue to be a challenge post-harvest if conditions are conducive.
  • For more on post-harvest disease management of powdery mildew and downy mildew see this article posted last year on the Wisconsin Fruit News website.

Maintain foliar health.

• Foliar health is especially important in our climate in Wisconsin with low winter temperatures, therefore season long control of foliar infections to minimize the risk for winter injury and reduce primary inoculum is critical.
• Leaves are not immune to infection by powdery mildew even as they expand, and while young, expanding leaves are most susceptible, large, expanded leaves can still harbor significant colonies of the powdery mildew fungus.  Similarly, leaves are most susceptible to downy mildew when emerging or expanding, however on highly susceptible varieties infections on expanded leaves still occurs and under conducive conditions these infections can become severe.
• It takes approximately 4 to 6 weeks of temperatures >32°F (frost-free) for late season powdery mildew infections to form overwintering structures (chasmothecia) before the leaves containing the fungus are killed. If weather conditions are conducive (frost-free, humid, and cloudy days) for a period between harvest and a frost event, consider what post-harvest protection may be needed on susceptible varieties.
• Hot, dry summer weather inactivates the downy mildew pathogen, so scout your vineyard post-harvest to determine if there is disease activity and assess the need for a fungicide application based on your observations.
• If your vineyard has experienced high disease pressure (powdery mildew or downy mildew), post-harvest fungicide sprays may be necessary to maintain control. Consult the Midwest Fruit Pest Management Guide or Organic Production and IPM Guide for Grapes for fungicide recommendations.
• Before pruning in winter monitor your vineyard for overwintering pathogens. Under conducive conditions in the following growing season these pathogens can become a serious problem. Minimize the risk of disease by practicing sanitation (i.e. removal of infected and dead tissue)
  • Stay tuned for a dormant season Wisconsin Fruit News article that provides images of overwintering fungal structures to aid in identification in your own vineyard.

This article was posted in Disease and tagged Apples, disease, Grapes, Leslie Holland, post-harvest disease, post-harvest disease management.