Posts Tagged: Pseudomonas syringae
CANCELLED: Tory Hendry Seminar on Bacteria That Infect and Kill Pea Aphids
(Editor's Note: This seminar initially set for Wednesday, May 2 at 4:10 p.m. in 122 Briggs Hall has...
A Pear Blossom Blast ...Not Fire Blight
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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Bacterial canker and blast damage appearing.
Prunes are just past petal fall, but I've been shown several examples of bacterial canker and/or blast in the last week (see pictures below).
These symptoms are caused by infections of Pseudomonas syringae pv. syringe, a common bacteria found throughout orchards. Particularly in years with cold wet winters/springs, the bacteria enter prune trees -- and other stone fruit and almonds -- damaging scaffolds (bacterial canker) and buds (bacterial blast). The bacterial blast generally is not a major economic issue for growers. However, canker can spread rapidly and kill trees from the top down. Strangely enough, the rootstock is not affected by the bacteria, and damaged trees often show vigorous sucker growth.
Once the symptoms appear, there is little to be done. Don't remove damaged trees when symptoms first show. The trees may recover.
Bacterial canker is associated with:
- Soil related stress such as acid soils, shallow soils over hardpan, or coarse texture (sandy) soils with nematode (specifically ring nematode) pressure. The bacteria don’t enter the plant through the soil – at least they don’t harm the rootstock, but soil stresses predispose the tree to above ground infection.
- Low soil nitrogen availability
- Pruning during wet, cool weather.
- Rootstock selection. M2624 is most sensitive to bacterial canker, although M29C is susceptible as well. M40 is reported to be the rootstock that is least susceptible to bacterial canker.
What can be done to avoid bacterial canker?
- Avoid soil stresses listed above, wherever possible.
- Spot fumigate to control nematodes in coarse texture (sandy) soils
- Maintain adequate soil nitrogen levels
- Prune in late summer/early fall or late spring
- Plant on M40 rootstock
Also, Jack Dibble, retired UCCE entomology specialist, told me that, in his experience, trees with bacterial canker pressure showed dormant oil burn more readily than trees not under pressure from bacterial canker. If your block is at risk from bacterial canker (sandy soils, low N levels, nematodes, etc.), consider avoiding high dormant oil rates.
Prune trees showing bacterial canker symptoms (scaffold collapse, gumming). Sutter Co. April 8, 2011
![TreeWSymptoms.sm TreeWSymptoms.sm](http://ucanr.org/blogs/PruneUpdatesCalifornia/blogfiles/6703.jpg)
Prune buds damaged by bacterial blast.
BlastedBuds.2.sm