Apple tree is afflicted by fire blight disease, more common now due to our wet summer.
Wet summers such as the one experienced this year in southern Manitoba encourages diseases such as fire blight and black rot, especially in fruit trees. Tree and woody shrub diseases normally show up in the spring or summer. Early detection of the disease can lead to its control. The standard method of early control of a visible disease is to prune it out of the plant. The pruning cut must be made at least 30 cm (one foot) away from the outer edge of the diseased portion of a twig or branch. The cut must be made as close as possible to a junction with another branch or stem. At these junction locations or nodes woody plants have a better opportunity to seal over the cut quickly if the right cut has been made.
I am often asked, "Do I need to paint over the cut?" In disease-susceptible trees such as all the edible fruit and ornamental fruiting trees, the pruning cuts should be sealed if those cuts were made in spring or summer. Here are some points to remember:
(1) Never use tree pruning paint nor any other type of paint (oil or latex) to seal the cuts. These products do not work, and oil-based paints can harm the tree.
(2) Use a proper tree-pruning seal product such as Later's Tree Pruning Seal or NuBark Pruning Seal Paste or Wilson Pruning Paste. These products might be available in garden centres in the spring and summer. They are rarely available in the fall as stock is often used up by the fall season. Always call the nursery or garden centre first to see if the product is available.
(3) After the diseased part of the branch has been pruned off, always disinfect the pruning tool before making the next cut in that diseased tree or shrub. Infected pruning tools will spread bacterial or fungal spores to the next pruning location. These spores are microscopic and they are not visible to the naked eye. What can be used to disinfect the pruning tools? In a used spray window cleaner spray bottle add either methyl hydrate (undiluted consumer grade), or rubbing alcohol, or diluted bleach (one part bleach to 9 parts water). Spray one of these products into the pivot cutting area of hand pruning and loping shears. Spray directly onto a pruning saw if that was used. (NB: if bleach and water are used the pruning tools must be oiled with WD 40 or something similar afterwards. The metal in the tools will rust otherwise. Some people dip their pruners directly into a bucket of bleach and water.)
(4) One of the most common questions I am asked: "When is the best time to prune healthy trees?" For the broad-leaved trees (often called deciduous or leaf dropping trees), the best times are in October through December, and again in late March and April. Never prune maples and birch in late winter or early spring as they will 'bleed' copious amounts of sap. Shaping and pruning live growth on coniferous evergreen trees and shrubs is best done in early June. Dead branches can be pruned any time.
Each early spring and fall period I give a number of course presentations on tree and woody shrub pruning and care. Call or email me for further information. Visit my website for more general information about these courses. The next series of courses start in March 2010.
Michael Allen M.Sc.F., RPF is a consulting urban forester and certified I.S.A. arborist. He owns Viburnum Tree Experts, He can be reached at 204-831-6503 or viburnumtrees@shaw.ca His website is www.treeexperts.mb.ca
