Ask a Master Gardener: Why pruning fruit trees is important

Who can believe the weather we are having? One thing that warmer weather is good for this time of the year is pruning your fruit trees. Late February through early March is the best time for pruning fruit trees.

With that in mind, here is some helpful information about fruit trees from Michele Warmund, University of Missouri Division of Plant Sciences:

"From February until early April, fruit trees grown in Missouri often become infected with a fungus (Leucostoma cinctum) that causes perennial canker. This fungus invades the bark during winter when temperatures are above freezing but stops when there is active tree growth in the spring.

"After infection, cankers with amber ooze become visible and can develop year-round. This pathogen is a secondary invader, requiring a wound for infection.

"Some of the common ways the pathogen enters trees is through wounds, such as bud scars or from twig lesions caused by brown rot, cracks in the bark from sun-scald or Southwest injury, feeding sites from Oriental fruit moth, borers or rodents and hail or mechanical injury.

"Once the tree is infected, spores are often found on the bark surface year-round. Young trees are most likely to succumb to perennial canker and may take three or more years to die.

"Since wounds are often unavoidable on fruit trees, the best way to guard against spread of the disease is to select cold hardy cultivars for planting and maintain tree health with cultural practices.

"Careful attention to tree nutrition, especially preventing nitrogen and potassium deficiencies, will help keep trees healthy. Submitting leaf samples for foliar analysis from July 15-Aug. 1 will help determine the tree nutrient status and the amount of fertilizer needed to maintain productive fruit trees.

"Late-winter pruning is also recommended to prevent premature deacclimation of trees. If possible, wait until just before buds begin to grow to prune. When pruning, avoid horizontal or flat cuts where water can collect and prolong infection periods.

"Also, prune healthy trees first and leave the infected ones until last to avoid spreading the disease. When pruning infected trees, disinfect the blades of the pruning tool between cuts. Household bleach (one part bleach plus three parts water), Pine-Sol cleaner (one part cleaner plus three parts water), or rubbing alcohol (one part 70 percent isopropyl alcohol plus one part water) can be used as disinfectants. Remove prunings from the area as soon as possible as the fungus lives and grows on dead tissues and will spread under rainy or windy conditions.

"During the growing season, avoid trunk wetting when watering fruit trees. Also, tree trunks can be painted with latex paint to prevent bark splitting, especially on the southwest side of the trees.

"Maintaining a weed-free area or cover crop at a low height during the growing season and in winter will also help reduce injury from rodent feeding. Wire tree guards around the base of the tree trunks year-round or plastic wrap-around tree guards placed on the lowest portion of the trunk from November through March will also reduce rodent damage.

"Plastic guards should be removed in the spring to speed drying of trunks after precipitation and to avoid creating a protected habitat for insects. Poultices of brown mustard plants or mustard oil have been evaluated as organic controls, but oil only protected peach trees for five months, and therefore these options may have limited practicality.

"When trees have small cankers (less than half the branch or trunk diameter) and dry weather is expected for at least three days, surgical removal may be feasible. During June, when rapid healing occurs, the dead bark tissue can be surgically removed."

Just a reminder, the Callaway County Master Gardeners will be holding a class on starting seeds for cole crops at 6 p.m. Feb. 28 at the Callaway County Library. The class is free and open to the public. See you there.

Happy gardening!

Peter Sutter is a lifelong gardening enthusiast and a participant in the MU Extension's Callaway County Master Gardener program. Gardening questions can be sent to [email protected].