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.
PLANT SALE! Mark your calendar for our plant sale onSaturday, May 18, 2024 from 9 am–noon. The sale will be held at the Master Gardeners Demonstration Garden at Patrick Ranch. The plants, which are selected to thrive in our climate, have been propagated by UC Master Gardeners of Butte County. For more information and a partial list of the plants that will available, visit our website.
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: Belinda Messenger-Sikes
After years of drought, we welcome rain in California. But we also recognize that rain can help spread a number of plant diseases. Rain and wind can splash bacteria and fungi from infected leaves, branches, and blossoms to uninfected parts of the tree. The fungal diseases anthracnose, peach leaf curl, scab, shot hole blight, and the bacterial disease fire blight can all be spread by rain splash. This ability to spread by water makes these diseases more common after a wet spring. With 2023 bringing quite a bit of rainfall and 2024 looking similarly wet, we want to focus on some common rain-dispersed diseases.
Anthracnose
Anthracnose affects many trees including almond, citrus, Chinese elm, and ash (Figure 1). In the spring, fungi produce spores on leaves and twigs that can be spread to new growth via water splashing. Under prolonged wet conditions, this cycle of spore production and spread can occur repeatedly. Anthracnose can defoliate trees, although it is not a lethal disease in most of its hosts. Once symptoms develop or become severe in a growing season, anthracnose can't be effectively controlled. It's best to rely on prevention of the disease by planting resistant varieties. For more information about identification and management of anthracnose, see Pest Notes: Anthracnose.
Fire blight
Pome fruit trees like pear and apple, and other related trees like pyracantha are often affected by fire blight. This destructive disease spreads in the early spring when rain splashes water from infected leaves and blossoms to healthy plant parts. Pollinators like bees can also spread the disease as they visit blossoms. Symptoms may not be noticeable until later when shoots and flowers shrivel and blacken. New growth is especially vulnerable to infection, so avoid heavy fertilization and pruning during mild wet weather.
The Pest Notes: Fire Blight contains much more detail on identification and management of this disease.
Peach leaf curl
Many home gardeners are familiar with the distorted, reddish leaves (Figure 2) caused by peach leaf curl, a disease that affects peach and nectarine trees. The fruit can also be damaged, becoming corky and cracked. Cool, wet weather favors the spread of the disease, but treatment must be started before the spring rains. Preventative sprays should occur after leaf drop but before flower buds swell. Resistant varieties are available to prevent this disease from occurring. Pest Notes: Peach Leaf Curl provides details about this disease and its treatment.
Scab
Various fungi cause the disease scab, which appears as spots and scabby blemishes on fruit and leaves. Apple scab is especially serious during wet springs and in the cool moist coastal areas of California, although these conditions are also conducive for development of other scab diseases. This disease can ruin the harvest of commercially grown apples and pears but in home gardens, some damage can be tolerated. Limit both apple and pear scab on backyard trees by removing and composting fallen leaves and fruit in the fall.
Information specifically about apple and pear scab can be found in the Pest Notes: Apple and Pear Scab. For more about other scab diseases, see http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/scab.html.
Shot hole blight
Shot hole blight, also known as Coryneum blight, is caused by the fungus Wilsonomyces carpophilus. It affects almonds, apricots, and other Prunus species, as well as English laurel. Symptoms appear in the spring as small reddish spots that turn brown and drop out, leaving holes in the leaves (Figure 3). Fruit and twigs can also be affected. Since this disease is worsened by continuous leaf wetting, avoid irrigating foliage. For more information, see the UC IPM page on shot hole blight at http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/DISEASE/shothole.html.
While you can't control the rain from spreading these diseases, good plant care and sanitation practices can help limit the severity. See the publications above as well as other pages on the UC IPM website to find out more.
[Originally featured in the Spring 2024 edition of the Home & Garden Pest Newsletter]
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- Author: Help Desk Team
Have you noticed burnt-looking blossoms and twigs on your apple, pear, or quince trees? This is likely caused by a bacterial infection, appropriately named fire blight. Fire blight can damage and even kill fruit trees in the Pome family and may affect other related species such as crabapple, ornamental pear, pyracantha, and toyon. It does not affect stone fruit, such as plum, peach, apricot, or cherries.
The disease is caused by a bacterium, Erwinia amylovora, which is most active during warm, wet spring weather. It enters the plant primarily through blossoms, but also through tender new shoots or bark wounded by mechanical injury or from strong hail and wind. It is spread by splashing water and pollinating insects, including bees. The pathogen is widespread in the environment but may not be much of a problem unless conditions are favorable. Older established trees can often withstand some fire blight damage, but young trees may be severely damaged.
The first sign of a fire blight infection may be dark and dried-up new shoots and young fruit, which soon turn black. You might also see watery, amber-colored droplets oozing from affected areas.
Fire blight may sometimes be confused with another condition, blossom blast, which also produces blackened flower clusters, but there are several symptoms characteristic of fire blight. On apples and pears, the tips of affected shoots develop a curved tip (‘Shepherd's Crook'). The scorched-looking young leaves and fruit do not fall off, but cling to the plant.
If a new fire blight infection is not removed in time, it spreads down through the wood, and bark cankers (areas of dead, discolored tissue) develop. If not removed, the infection in these areas persists from year to year.
Fire blight is not easy to control, but there are a few things you can do to manage this disease. Examine your trees regularly so you notice the first signs of a strike; the new shoots start to turn brown and droopy even before they become black. These shoots should be removed right away, cutting far enough below the infection to where no brown or discolored areas are seen. Use sharp pruners, disinfecting them between each cut. Use a 10% bleach solution or Lysol for disinfecting.
The disease becomes inactive during the summer and winter when bark cankers harboring the pathogen may be seen. These can be removed by pruning out diseased wood, at least 6–10 inches below the visible infection, or back to the branch connection with a larger branch or the trunk. If the canker is on a large limb or the trunk but does not girdle the branch, you can try scraping the bark away until no more discoloration is seen. Dispose of all infected material in the trash and not in the compost!
When fire blight is a problem from year to year, you can use a copper spray on the blossoms. This helps to prevent new infections but is not very effective if the pathogen is already in the tree. Such sprays can also cause russeting damage on the fruit.
When planting new trees, consider varieties that are more resistant to fire blight such as Arkansas Black or Cox's Orange Pippin. Unfortunately, many of our favorite varieties such as Pink Lady and Fuji, and most pears, are very susceptible. Tender new growth on a tree is more likely to suffer, so avoid practices that encourage this such as excess fertilizing and pruning. Also, don't irrigate while the tree is blooming.
This UC website provides more detailed information on fire blight and how to manage it.
https://ipm.ucanr.edu/PMG/PESTNOTES/pn7414.html
Help Desk of the UC Master Gardeners of Contra Costa County (SMW)
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.
It is critical to make your cuts in the right place. Find the lower edge of the visible infection in the branch, trace that back to the branch's point of attachment and cut at the next branch juncture down without harming the branch collar (the distinct enlarged portion of woody tissue formed at the base of a branch where it attaches to the trunk). This will remove the infected branch and the branch to which it is attached.
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.
PLANT SALE! Mark your calendar for our plant sale on Sunday, May 14, 2023 from 9 am–noon. The sale will be held at the Master Gardener Demonstration Garden at Patrick Ranch, 10381 Midway, Durham. The plants, which are selected to thrive in our climate, have been propagated by UC Master Gardeners of Butte County. For more information and a list of the plants that will available, go to Plant Sale - UC Master Gardeners of Butte County (ucanr.edu).
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) 538-7201. 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.
By Lynnde Sharpton, UC Master Gardener of Butte County, June 1, 2018
Fire blight is caused by a bacterium and is a common and frequently destructive disease that shows up in April and May. Fire blight can also affect pyracantha, ornamental pear trees, and some other landscape plants.
The first sign of fire blight is often 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.
It is critical to make your cuts in the right place. Find the lower edge of the visible infection in the branch, trace that back to the branch's point of attachment and cut at the next branch juncture down without harming the branch collar (this is the distinct enlarged portion of woody tissue formed at the base of a branch where it attaches to the trunk). This will remove the infected branch and the branch to which it is attached.
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.
For more detailed information on identifying and controlling fire blight, see IPM Fire Blight Pest Notes.