|Apple scab on fruit and leaves. Photos by C.J. Walke.|
By C.J. Walke
Autumn is an exciting time in the orchard, because you get to taste the fruits of your labors and share the harvest with your family and community. Autumn is also the time to clean up the orchard, prepare trees for winter and start thinking about next year’s bloom!
Apple scab, a major fungal disease of apple trees, can in extreme cases destroy fruit and defoliate trees. Infections start in early spring and spread throughout summer. At harvest you will see leaves with raised dark lesions and fruit with dark “scabs” and even cracks in the skin. Materials approved by the Organic Materials Review Institute to combat scab in organic orchards include mineral fungicides, such as sulfur and lime sulfur, which are applied from early spring through summer, but these may not be practical for the home or small orchard. In the organic orchard, an effective way to control apple (and pear) scab is to reduce the amount of overwintering fungal inoculum that is ready to infect young trees the next spring.
Scab overwinters on infected fallen leaves and infected fruit, so at harvest, don’t leave any infected fruit on the tree, since these will mummify (become hard, black and wrinkled) and can be a source of inoculum the next spring. When leaves start falling from the tree, speed their decomposition by mowing them to increase their surface area; and spread compost to boost populations of microbes, which also decompose leaves and help reduce overwintering inoculum.
I do not use mineral fungicides, but rely on orchard sanitation to limit scab in MOFGA’s orchards. I remove all fruit at harvest and return to the trees after the leaves have fallen and the trees are bare to make sure I didn’t miss any. At roughly 50 percent leaf fall, I lightly spread compost under the trees and mow the orchard to break up leaves and mix up the compost. I mow a second time when leaf fall is complete to shred the rest of the leaves. I don’t spread compost a second time; once is probably enough, since the compost is still there and active. If you have just a few trees, you can rake and dispose of leaves for more thorough control.
After harvest – by the end of October – I set rectangular hay bales throughout the orchard where field mice can nest in the winter. The mice depart come spring, leaving an excellent place for bumblebee queens to nest. Bumblebee queens key in on the scent of mouse urine, and bumblebees are very efficient pollinators come spring bloom time.
Fall is the time to remove any traps remaining in the orchard, such as red sticky balls for apple maggot fly control, if you haven’t already. Also remove any limb spreaders set in younger trees to establish good scaffolding branches. The limbs are hardened off by now and should stay put once spreaders are removed. Anything left in the trees over winter may blow around and rub off buds or accumulate snow and ice and break branches.
The most important orchard chore to prepare for winter is protecting the tender trunk bark on young trees from hungry meadow voles. Voles can seriously damage or girdle and kill young trees by eating the bark and cambium layer at the base of the tree. Once the tree is girdled, water and nutrients can no longer move up and down the trunk, and the tree will die. A girdled tree will usually leaf out in the spring, and you’ll think it survived the gnawing, but it is using energy stored in buds and bark to leaf out. Once that energy is consumed, the leaves will turn brown and the tree will die. Bridge grafting in April is the best – but not guaranteed – way to try to save the girdled tree.
To avoid losing a young tree, place vole guards around trunks before the first snowfall. This barrier prevents voles from eating the bark. Spiral plastic guards wrap around the tree trunk but must be removed in spring, since they can harbor insects and diseases if left. Plastic or metal mesh guards are loose fitting and can stay on year-round as long as you can enlarge them as the tree grows. Another trick is to compact the snow around trees with snowshoes so that it freezes into a hard ice pack. Voles cannot tunnel through this to get to the trees.
Once the snow starts to fly, sit by the fire and start planning for the following orchard season.