Crisp fall air, fresh cider and prime apple picking and pie-making season have all come and gone. The last of the late-season apples have been picked and stored. The killing frost may have arrived, and perhaps the first snowfall, depending on your region. The orchard, as well as the orchardist, are ready for a long winter’s nap.
Not so fast.
Best management practices for preparing the orchard for the winter involve overall sanitation and removal of debris; soil testing; precautionary measures to guard against animal damage, disease and pest concerns; and preventive steps to protect trees from ice, snow, sun and wind damage.
“Typically we talk about removing all fruit from the orchard, and not leaving any on the trees,” said C.J. Walke, of the Maine Organic Farmers and Gardeners Association (MOFGA). Walke advises organic growers on orchard care and manages two orchards at MOFGA’s Common Ground Education Center, in Unity, Maine. “Orchard sanitation is important because apple scab over-winters on infected leaves and fruits. Cleaning up the debris in the fall reduces the amount of disease present in the spring.”
Practicing preventative orchard care while establishing and maintaining a healthy, biologically active soil is the basis of successful organic tree fruit production. Although conventional growers have additional tools in their repertoire, the organic growing practices of building soil health as a baseline to tree and fruit productivity is one that benefits all growers, and late fall is the perfect time to start.
Building healthy soil
Orchards require a soil with a robust, beneficial fungal population, which dominates the bacterial presence. Walke recommends late fall mowing of the orchard floor to help decompose orchard leaf litter and add organic matter to the soil. Applying nitrogen or compost now will boost microbial activity in the soil, optimizing the decomposition of the mowed leaf litter, he said. A fish oil spray can be applied to help hasten leaf decomposition.
“We can spend a lot of time battling insects and diseases in the orchard, but if the tree is not rooted in a healthy, biologically active soil, then it will always be under some stress. Lacking nutrients, moisture and or good aeration, the health of the tree will be compromised, making it more susceptible to pest pressures,” Walke wrote on the MOFGA website.
Most soil fertility amending is best done in the spring, as increased nitrogen levels can cause winter issues in young trees. But correcting for pH via the spreading of lime is easily done in the fall and won’t negatively impact winter survival. Testing soils now provides a baseline reading for corrective action, although the most accurate nutrient levels are determined via mid-summer leaf analysis, Walke said.
“Other late fall activities in an organic orchard are spreading compost and wood chips around the trees to build soil, add organic matter and build fungal activity in the soil,” Walke said.
Preventing tree injury
The best strategy to prevent winter injury on limbs, whether from ice, snow or wind, is to have a good annual pruning program in place, Walke said. Beyond that, if any trees have limb spreaders, remove them before the winter weather arrives. Any insect monitoring traps need to be removed as well, along with anything else that adds additional weight to the branches.
Some orchard pest pressures increase in the winter, including damage from voles. Walke recommends pulling back mulch from the trunks and putting vole guards in place. Deer are a major pest in many areas, and if the orchard is not fenced, caging individual trees can be an option, although it may not be feasible in larger orchards, Walke said.
Penn State Extension’s Tree Fruit Production team provides information on deer management in the orchard, and warns growers of the harm that deer often cause during the winter.
“Dwarf, semidwarf and young standard fruit trees are the most susceptible because most of the tree is within reach of the deer. In winter, browsing on dormant terminal buds may lead to stunted or misshapen growth in standard fruit trees under 3 years old. Browsing on fruit buds of dwarf and semidwarf trees may lower fruit production. In either case, severe winter browsing can reduce tree vitality and even cause death.” For more, visit Penn State Extenstion’s Tree Fruit Production page.
Trees can be injured by sun scald, commonly known as southwest injury, Walke said. This damage causes frost cracks in the trunks of trees, potentially allowing infectious agents to enter.
“Sun scald or southwest injury is probably the toughest one to prevent,” he said. “This is where the trunk of the tree warms in the day from sun reflection off snow, then cools rapidly at night, and the same cycle happens day after day. Smaller scale growers might paint the tree white to reflect that daytime heat, but organic growers are limited on what materials they can use to paint the tree.”
Winter kill on young shoot tips is another concern. Winter winds can be too strong and dry for a young shoot, causing some die back. Other tree damage can be caused by fall nitrogen application, which prevents hardening off from occurring. The amount of nitrogen used to enhance fall leaf decomposition is not enough to cause concern, however, Walke said.
Sanitation can prevent some overwintering disease concerns, like apple scab. Others issues such as peach leaf curl, can be treated with late fall-applied sulfur sprays, to kill the spores that can overwinter in trees. Pear leaf blister mite is combatted with an oil spray to smother the eggs and adults that remain in the tree, and a fall application can be warranted.
“If pest pressures are high, you may want to make applications in late fall and early spring,” Walke said of dormant oil sprays, which are typically applied in the spring.
Implementing proactive orchard health strategies now before putting the orchard to bed rather than reacting to problems later, is a practice that every grower should utilize. MOFGA has a simple calendar of year-round apple orchard care, written by Walke.