- 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)
Help for the Gardener from the
Contra Costa Master Gardeners' Help Desk
Description of Client's Problem:
Here's the advice that the Master Gardener Help Desk gave the client.
It appears that the problem is Pear Blossom Blast (Pseudomonas syringae) not Fire Blight as we originally thought.
Blossom blast and die back is caused by a bacterial infection and very difficult to treat. Infected buds fail to open, dry out and die. Leaves may be spotted. Flower petals and stems may also be affected, and fruit cluster bases can turn brown or black. Occasionally, fruiting spurs may be killed. Cankers may develop in twigs and branches.
Symptoms of this disease, especially on flowers, may closely resemble fire blight. However, blast infections seldom extend more than 1"-2" into a spur. Bacterial ooze, which is common with fire blight, is not present with Pear Blossom Blast and none could be seen on your samples or pictures. Frost and cold injury promote infection (we did have some pretty cold spells this year). Warm, dry weather inhibits this disease.
Selecting non-chemical management options should be your first choice:
- Avoid wounding plants. (weed wacker too close, branches rubbing, etc.)
- Prevent frost injury when possible. Plant hardy varieties in protected locations.
- Provide proper culture to minimize succulent shoot growth and to reduce injuries.
- Prune out and destroy infected tissues as soon as they are noticed. Make cuts at least 6" below infected areas and sterilize pruning tools between cuts.
Bacterial Blossom Blast is difficult to control. Monitor temperatures and protect against frost, which may help prevent infection. In areas where Blossom Blast is common, copper sprays labeled for this use may be applied in the fall or dormant season, but the efficacy of these treatments is questionable.
Some additional information on Pear Blossom Blast can be found on the UC IPM web site at:
http://www.ipm.ucdavis.edu/PMG/r603100111.html#MANAGEMENT
Editor's Note: Each month the CCMG Help Desk's Quality Assurance Team selects responses to county residents' Help Desk questions that produced informative responses that are either unique or unusual, or provided updated information that would be informative to all gardeners, or are of general interest, especially of seasonal concerns. We are highlighting these responses in the HortCOCO blog so all interested Master Gardeners and the public may utilize the information.
The CCMG Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/
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