It’s that time of year again! While your trees are dormant this winter, it’s a great time to continue disease prevention practices in your apple orchard. Mummied fruits (Figure 1), fallen leaves, and damaged, decaying, or dead wood can be inviting places for pathogens to overwinter. Several fungal pathogens produce fruiting bodies that overwinter in those tissues, and when spring arrives, conducive conditions like rain and wind can spread fungal spores and cause new infections in healthy tissues. Fire blight “holdover” cankers can also serve as a source of bacterial inoculum in the spring if they are not removed during winter pruning.

Where do pathogens overwinter?

Disease	Overwintering location of pathogens
Apple Scab	Fallen leaves
Fire Blight	“Holdover” cankers on twigs, branches, or tree trunks
Flyspeck and Sooty Blotch	Dead twigs and branches
Bitter Rot	Mummified fruit, cankers, dead wood & branches affected by fire blight
Black Rot	Mummified fruit, cankers, dead wood & branches affected by fire blight
White Rot	Cankers, bark, mummified fruit

The goal of winter sanitation is to reduce the amount of inoculum in the orchard while fungi are inactive. This limits the re-introduction of pathogens when conditions are conducive in the spring.

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Winter sanitation checklist:

• Prune out dead, damaged, and diseased tissue (Figures 2 and 3). This includes the removal of fire blight “holdover” cankers.
  • Prune during dry periods.
  • Make clean and smooth pruning cuts, leaving no stubs. Keep the collar intact; cutting too close to the point of attachment can be damaging.
• Remove mummies from the tree canopy.
• Sanitize your pruning equipment to prevent the spread of the pathogens.
• Remove pruning’s from the perimeter of the orchard and destroy them by chopping, burning (where allowed, check local ordinance), or burying.
• Remove dead stumps and brush piles from the orchard, as these are potential reservoirs of fungal inoculum.
• Flag trunks with symptoms of cankers (i.e., sunken and peeling bark tissue; Figure 4) and monitor those trees during the following growing season.
• ***Apple scab management should be considered during the fall immediately after leaf fall or in the spring before budbreak.

Tips for Silver Leaf:

• Remove branches where conks (shelf fungi) are present. Cut at least 4 inches below where you can see staining under the bark. Removing branches with conks will limit spore production.
• Only removing the conks themselves will not have any impact on the growth of the fungus or save the tree they are growing on. By the time these conks show up on the outside of the bark, extensive damage of the wood has already occurred.
• If several trees are showing symptoms, mark diseased trees and keep an eye on their vigor.
  • Some infections can be compartmentalized by the tree, preventing further spread of the infection, and symptoms may go away in successive seasons.
  • Some infections will result in tree mortality and these trees should be removed.
• Sanitize pruning tools in 70% ethanal or a 10% bleach solution for 30 seconds. (Note: bleach can be corrosive to pruning equipment if not thoroughly rinsed).
• Avoid pruning during wet periods.

We want your cankered branches!

Our lab is conducting a study to investigate the fungi associated with branch cankers. During your winter pruning if you have cankered branches that you are willing to part with, please reach out to our program’s lab manager, Emma Nelson, at emnelson9@wisc.edu and we will stop by to pick them up.

This article was posted in Apples, Disease and tagged Apple Scab, Apples, Bitter Rot, Black Rot, disease, Emma Nelson, Fire Blight, flyspeck, Leslie Holland, sooty blotch, winter sanitation.