If you are noticing droopy, dried-out flower clusters on your pears, Asian pears, quince, apples or crabapples, fire blight may be the cause.
The first sign of fire blight is often the blackening of flowers, shoots or leaves followed by a watery, light tan ooze from affected shoots. Open flowers are the most common infection site and remain susceptible until petal fall.
Initially, fire blight infections might be localized, affecting only a flower cluster, but then the infection grows downward, extending into twigs and branches. These twig cankers kill more and more tissue as they advance. Dead, blackened leaves and fruit cling to dead branches throughout the season, giving the tree a scorched appearance -- hence the name “fire blight.” The pathogen can kill highly susceptible trees, while others may suffer significant branch dieback. Once infected, the plant will harbor the pathogen indefinitely unless the cankers are pruned out well below the infection.
Monitoring trees regularly, a couple of times a week, will allow you to identify and deal with new fire blight strikes before they become a branch infection. It is important to remove and destroy any new fire blight infections before they spread and affect more tissue. Dip pruning shears in a 10-percent bleach solution after each cut.
If fire blight strikes have been ignored, the infection will spread and infect the branch. Once the wood is infected, the branch must be pruned out well below the infection. In this case, you will need to remove the diseased wood in summer or winter when the bacteria are no longer spreading through the tree. Again, dip pruning shears in a 10-percent bleach solution after each cut.
If fire blight occurs on a trunk or major limb the wood may be saved by scraping away the bark down to the cambium layer in affected areas (removing both outer and inner bark). When scraping look for long, narrow infections that can extend farther down the branch or trunk. If any are seen, remove all discolored tissue plus six to eight inches more beyond the infection. This procedure is best done in winter when trees are dormant and bacteria aren't active. Don't apply any dressing to the wound. If the limb has been girdled, scraping won't work and the entire limb must be removed.
When selecting new fruit trees, choose those that are less susceptible to fire blight, if possible. The most susceptible varieties are Fuji, Gala, Golden Delicious, Granny Smith, Gravenstein, Jonathan, Mutsu, Pink Lady and Yellow Newton. Unfortunately, most pear varieties are susceptible to fire blight.
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UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at 530-552-5812. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us section of our website.
- Author: Steve Radosevich
Most of us who grow fruit trees think of pruning as a winter practice, done when the tree is dormant and leafless, and the tree skeleton can be better observed. Although dormant pruning is called for on most deciduous fruit trees, some additional summer pruning may help you maintain the tree size that you want in your backyard. Unlike dormant pruning, cutting off actively growing shoots and leaves in the spring and summer has a devigorating effect on the tree and will help control its size.
The Fruit Bush system, a method of pruning that keeps standard-size trees or trees on dwarfing rootstock small, relies on periodic summer pruning. The first pruning is done in late April or May when half of the new growth from that season is removed. A second similar pruning is done in June, and if vigorous growth continues, a third pruning is done in late July or early August.
This type of pruning results in a tree that is bushy in appearance, with a dense interior canopy that requires additional pruning so that sunlight can reach the lower fruiting branches. However, it is important to leave enough foliage to protect the tree from sunburn.
Fruit bushes are often kept at a height that allows you to do all your tree care - pruning, thinning, netting, picking, spraying - without using a ladder. With the use of this pruning system, trees can be planted much closer together, allowing you to plant more fruit trees in a small space. For more information on the fruit bush system go to https://anrcatalog.ucanr.edu/pdf/8057.pdf . Fruit Trees: Training and Pruning Deciduous Trees.
Summer pruning is particularly recommended for apricots, to avoid a common branch-killing disease called Eutypa dieback, which can develop on pruning wounds that are made during wet weather. Try to do all your pruning on apricot trees in July or August. If some dormant pruning is still needed, wait until late in the dormant season.
For more information on summer pruning, as well as other summer tasks in the home orchard go to https://ucanr.edu/sites/ucmgplacer/files/171595.pdf for a two page publication Summer Care of Fruit Trees by Master Gardener Mike Kluk. Another free publication on pruning and training fruit trees can be found at https://homeorchard.ucanr.edu/The_Big_Picture/Pruning_&_Training .