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25 July 2012
Results of Collection of Fire Blight Samples for Streptomycin Sensitivity Assays
You may have forgotten about the request in April for fire blight samples to assay whether there is resistance to streptomycin in the bacterium Erwinia amylovora in NC orchards [see below]. The assays were completed last week. The statements below provide a summary of the results. I want thank Dr. Mike Parker and Mr. Gene Klimstra for collecting samples and also coordinating the collection and getting the samples to me in Raleigh.
There will be more information provided concerning fire blight and management stragies for 2013 season presented at the APPLE AND PEACH Field Day at the MHCRS, Mills River, next Tuesday, July 31.
SURVEY FOR POTENTIAL FIRE BLIGHT BACTERIA (Erwinia amylovora) RESISTANT TO STREPTOMYCIN
To survey for the potential of orchards having fire blight bacteria resistant to streptomycin, disease samples were collected during the week of April 30 – May 3, 2012. The sample collection was coordinated by Dr. Mike Parker and Mr. Gene Klimstra (thank you). Samples were collected from orchards in up-state South Carolina, Polk county, Henderson county, and Lincoln and Cleveland counties. In early June, disease samples were collected from orchards at the Mountain Horticultural Crops Research Station, Mills River, NC, Wilkes/Alexander, and Cleveland counties. There were 42 fire blight samples (someone sneaked in a plum sample! Fruit had frozen.), most were apples and a couple were pears. Bacteria were isolated from all samples although it was not possible to obtain E. amylovora from all samples. Up to five individual bacterial colonies from each sample were combined for assay. Bacteria were tested on green pear slices for bacterial ooze production and compared to an E. amylovora isolate that had been confirmed as E. amylovora by the NCSU Plant Disease and Insect Clinic. These were than stored at -80C until assayed.
In July, bacteria were assayed against three concentrations of streptomycin sulfate; 10, 50, and 100 ppm. Two bacterial strains, one known to be resistant to streptomycin and the other sensitive to streptomycin were used as controls. None of the E. amylovora bacteria were detected to be resistant to streptomycin. All were sensitive starting at the 10 ppm rate. This does not mean that there may not be streptomycin resistance E. amylovora strains in NC orchards, but none were detected in these samples. Many of the non-E. amylovora bacteria were resistant to the 100 ppm rate. The significance of this is open for discussion, but does indicate that there is a genetic source of streptomycin-resistance genes in the environment. If the use of streptomycin is abused (excessive use and in post-bloom sprays except when trauma blight occurs), the potential is there for resistance to occur in E. amylovora.
30 April 2012
Collection of Fire Blight Samples for Streptomycin Sensitivity Assays
Dr. Mike Parker will be in Henderson County this week and has offered to bring fire blight samples back to Raleigh on Thursday. Also, Travis Nix at Helena Chemical on Rt 64 in Henderson County has offered to serve as a collection center for the samples. Thanks to both Mike and Travis, this will be a way to get samples to Raleigh without costs for mailing or shipping.
Thus any grower (apple and pear) in whose orchard fire blight has occurred and who would like to have samples assayed for sensitivity to streptomycin can bring samples to Travis by Thursday morning. Collect and label samples as directed below. Gower confidentially will be observed and names or individual orchard locations will NOT be disclosed without grower permission.
Samples can consist of both blossom blight (especially the canker at the base of the flower cluster) and terminal blight. For blossom blight, try to collect a diseased sample that includes the canker. For terminal blight, provide several inches (probably not more than 6 inches) including 1 to 2 inches beyond the margin of the canker. Collect up to 5 samples from up to 4 locations within an orchard. The samples should be placed in a plastic bag (e.g. sandwich baggie) that is loosely closed. Do not try to make it air tight and do not place moist paper (towels) in the bag. Once collected, the sample(s) should be placed out of sunlight and in a cool location, a refrigerator would be ideal. Be sure to provide some type of identification so that a trace-back to the orchard can be made. Assay results are not intended for the 2012 season but if resistance is detected this could have use for the 2013 season.
April 25, 2012
Given the incidence of fire blight (blossom and terminal) that occurred this spring in some locations, it seems an appropriate time to assay the Erwinia amylovora bacterial population for the presence of strains that potentially may have decreased sensitivity or potentially may be resistant to streptomycin. However, the following is a simplified procedure and thus may not detect resistant strains unless they are very common within an orchard.
If you have growers whose orchards have fire blight and would like to have disease samples assayed, I have arranged for the NCSU Plant Disease & Insect Clinic to receive these and not charge for the sample. This will apply only to fire blight samples from what are deemed to be commercial orchards. These samples will be diagnosed and assayed ONLY for fire blight.
Samples can consist of both blossom blight (especially the canker at the base of the flower cluster) and terminal blight. For blossom blight, try to collect a diseased sample that includes the canker. For terminal blight, provide several inches (not more than 6 inches) including the margin of the canker. The samples should be placed in a plastic bag (eg sandwich baggie) that is loosely closed. Do not try to make it air tight and do not place moist paper (towels) in the bag. Once collected, the sample(s) should be placed out of sunlight and in a cool location, a refrigerator would be ideal. Samples should be sent to the Clinic within 5 days of collecting. Collect up to 5 samples from up to 4 locations within an orchard. Be sure to provide some type of identification so that a trace-back to the orchard can be made. Assay results are not intended for the 2012 season but if resistance is detected this could have use for the 2013 season.
Any questions or comments should be sent to Dave Ritchie and not to the Clinic.
SEND SAMPLES TO:
Address for US Postal Service, UPS & FedEx:
ATT: Dave Ritchie
Plant Disease and Insect Clinic
Campus Box 7211
100 Derieux Place
1227 Gardner Hall
North Carolina State University
Raleigh, NC 27695-7211
State Courier Address:
ATT: Dave Ritchie
Plant Disease and Insect Clinic
Campus Box 7211 NCSU
Raleigh, NC 27695
STATE COURIER: 53-61-21
15 April 2012
Dave Ritchie
Plant Pathology Extension
Hail in some locations and freeze damage in others combined with fire blight blossom infections and rapidly growing terminals create a high risk for shoot/terminal infections. Weather forecasts also indicate a chance of precipitation for most areas starting early in the week.
Thanks to communication with Dr. Sutton, I am providing the following suggestions:
In orchards with little or no crop or hail damaged fruit, copper alone can be used. We do not think that including steptomycin would add much and increases the risk for resistance developing. Streptomycin use, however, may be considered where rat-tail bloom occurs and conditions for fire blight become favorable (precipitation and average temperature 60F or greater). It is suggested that 0.20-0.25 lb metallic copper equivalent (MCE)/acre be used in one or two applications - depending on rainfall. For Kocide 3000, which has 30% MCE, this would mean 0.67-0.83 lb of product/acre. For Cuprofix ULTRA 40, which has 40% MCE, this would mean 0.50-0.625 lb of product/acre. Similar calculations can be done for other formulations of copper – the MCE can be found on the product labels. If you go up to 0.50 lb MCE/acre, you will begin to get some fruit spotting. Of course without any crop or a hail damaged crop it probably doesn't matter a lot. Romes are pretty tolerant of copper, but the lighter skinned varieties are more sensitive. The important thing to reduce the risk of phytotoxicity is to apply copper materials under good drying conditions. Also multiple applications are probably ok if there it rainfall between applications. Without rainfall, copper can buildup causing phytotoxicity. BE SURE COPPER RATES/ACRE ARE PROPERLY CALCULATED AND USED TO AVOID UNNECESSARY PHYTOTOXICITY.
Terminal/shoot blight can be particularly damaging for young trees especially if on size-controlling rootstocks as the infection can “run” into scaffold limbs and the central leader or rootstock killing the tree. Monitor young trees for shoot blight and remove immediately making the cut several inches ahead of the infection and using appropriate sanitizing methods of pruning shears.
Insects such as aphids are important in transmitting fire blight bacteria to growing terminals and you should monitor for such taking appropriate action when needed.
I am considering asking for fire blight samples in the next few weeks. I will send out further information about this later.
Monday, 9 April 2012
Dave Ritchie
Plant Pathology Extension
Apple bloom period should be nearly completed, if not completed, except for Romes. Thus I do not intend to send out additional blossom blight forecasts. Also, at this time, the forecast into next week looks relatively dry unlike was predicted last Friday.
In communications with colleagues in other states this morning, they indicate that the number of days, particularly consecutive days (8 days in Polk county) with infections indicated by MaryBlyt is quite unusual. Thus, the potential is there to have had significant amount of blossom blight this year. This should be showing up in some locations. Given the warm temperatures that have occurred, MaryBlyt predicts symptoms about 7-10 days after infection.
In addition to killing blossoms, blossom blight infections provide a source of bacteria to cause twig/shoot blight. This can present serious problems for susceptible varieties especially if on susceptible size-controlling rootstocks.
Dr. Sutton in past years has recommended Apogee for susceptible varieties on size-controlling rootstocks. It is getting a bit late for use of Apogee to effectively control fire blight but there is information on use of Apogee on page 71 of the 2012 Integrated Orchard Management Guide for Commercial Apples in the Southeast.
Friday, 6 April 2012
Dave Ritchie
Plant Pathology Extension
I ran MaryBlyt using weather conditions through this morning (Friday, 6 April).
It apparently has been quite a season so far for fire blight based on MaryBlyt forecasts as are summarized below.
THERE IS A FROST ADVISORY FOR TONIGHT (6 APRIL) FOR ALL THREE LOCATIONS. Frost damage can cause “trauma blight” when bacterial populations on foliage are high. Streptomycin, applied within the past 48 hours, should help reduce risk if frost damage occurs. Another spray should be considered if frost damage occurs, particularly if blossom blight has been observed in the orchard.
POLK COUNTY (Columbus): For the purpose of the Model, bloom was started 18 March. Since then the Model has predicted there were 13 days when conditions were favorable for blossom infection assuming no sprays were applied. The latest occurred Thursday, 5 April.
HICKORY AREA (Airport data): For the purpose of the Model, bloom was started 20 March. Since then the Model has predicted there were 7 days when conditions were favorable for blossom infection assuming no sprays were applied. The latest occurred Tuesday, 3 April.
HENDERSON COUNTY (Edneyville station): For the purpose of the Model, bloom was started 2 March. Since then the Model has predicted there were 6 days when conditions were favorable for blossom infection assuming no sprays were applied. The latest occurred Thursday, 5 April.
Weather conditions are forecast as dry with high temperatures 60s to 70sF and lows after tonight upper 40s to mid-50sF. Forecast for rain comes back next week on Thursday – Saturday with Friday at 70% for most areas.
The next few days will be a good time to assess the blossom blight situation.
DON'T FORGET ABOUT APPLE SCAB!
Monday, 2 April 2012
Dave Ritchie
Plant Pathology Extension
I just ran MaryBlyt using weather conditions through this morning (Monday 2 April).
For all three areas where rainfall occurred (this is apparently all areas), MaryBlyt predicts that fire blight blossom infection occurred. MaryBlyt also predicts that a spray prior to rainfall starting last Friday prevented infection and gave protection for approximately 2 days. In some areas, rainfall occurred every day since Friday including this morning at Hickory.
For all three areas: Polk County -Columbus station, Hickory - airport station, and Henderson County - Edneyville station; as long as bloom continues and with the next rainfall event another INFECTION IS PREDICATED.
Friday, 30 March 2012
Dave Ritchie
Plant Pathology Extension
I just ran MaryBlyt using weather conditions through this morning (Friday, 30 March).
For all three areas, fire blight RISK HIGH. The forecast is for 50% chance of rainfall today and tonight. Thus if rainfall occurs, an infection is predicated.
HICKORY: In this area, the model indicates there have been 3 days (23, 24, 25 Mar) with fire blight infection. The forecast is for 50% chance of rainfall today and tonight. The current RISK HIGH, thus if rainfall occurs, an infection is predicated.
POLK COUNTY: The Model indicates that since 19 March there have been 6 days (19, 22-25, 29 Mar) with fire blight infection. There was 0.03 inch of rainfall yesterday/last night at the weather station indicating the latest infection within the past 24 hours. The forecast is for 50% chance of rainfall today and tonight. Current RISK HIGH, thus if rainfall occurs, an infection is predicated.
HENDERSON COUNTY: The model indicates HIGH RISK and if rainfall occurs, fire blight infection is predicated. This is the FIRST infection indicated for the Edneyville area this season. The forecast is for 50% chance of rainfall today and tonight. The current RISK HIGH, thus if rainfall occurs, an infection is predicated.
****APPLE SCAB – also stay alert for apple scab infection.
Monday 26 March 2012
Dave Ritchie
Plant Pathology Extension
This past weekend, actually from Thursday – Sunday, most if not all apple growing areas experienced significant periods of precipitation. This creates major concern for fire blight and also apple scab.
I just ran MaryBlyt using weather conditions through today (Monday, 26 March).
POLK COUNTY: The Model indicates that fire blight infection occurred every day starting 22 March (Thursday) and continued through 25 March (Sunday). I did not run the Model using data from Hickory, but I suspect that the same occurred in that area.
HENDERSON COUNTY: Although the Model indicated HIGH RISK it does NOT indicate a fire blight infection period using data from the weather station in the Edneyville area. The minimum temperatures were in the mid- to low 50s and maximum temperatures around 70 except on Sunday when the maximum was 58. I suspect that in areas of the County where temperatures could have been warmer, some infection may have occurred.
****APPLE SCAB – just a warning about apple scab. Temperatures may have been a bit cool for fire blight but they were favorable for apple scab infection especially of the calyx. I would suggest that you check the recommendations in the Apple Spray Guide as what to do if you think there has been a scab infection in your orchard as there are eradicant fungicides.
Friday, March 23, 2012
Dave Ritchie
Plant Pathology Extension
FIRE BLIGHT RISK AS OF 23 MARCH 2012 ---
MaryBlyt model was run at noon today using data from Hickory (airport), Polk (Columbus) and Henderson (Edneyville) Counties. Bloom has started (some blossoms open) in all three counties depending on location within the county and the variety.
HICKORY AREA: There was no recorded precipitation through noon today (23 March) since 18 March. Based on temperature and bloom stage, for 21 March – noon today MaryBlyt predicts HIGH RISK. If as little as 0.01 inch of precipitation occurs, the Model predicates INFECTION. The weather forecast is for 70-80% precipitation today and tonight, 60% chance on Saturday, and 40% chance on Sunday. The forecast Monday – Friday of next week is clear or partly cloudy.
POLK COUNTY: On 18 March there was 0.26 inches of rainfall for the weather site. At that time the Model predicated HIGH RISK. The Model then predicated that an INFECTION OCCURRED if susceptible blossoms were open. The Model predicates INFECTION this weekend again if or where blossoms are open. Granny Smiths are blooming. The forecast Monday – Friday of next week is clear or partly cloudy.
HENDERSON COUNTY: The temperatures and growth (bloom) are holding infection back. Predicated RISK HIGH, but the Model does not predict infection. Precipitation is predicted today through Sunday. The forecast Monday – Friday of next week is clear or partly cloudy.
My conclusions as of today, 23 March, are that the areas with greatest risk for infection this weekend are in Polk and Lincoln-Cleveland areas where Granny Smiths have the most open blossoms plus a few other varieties are opening. The forecast for next week looks dry through Friday and cooler early in the week, with the chance of precipitation and warmer by the weekend. Thus, next weekend with many more blossoms open could be a HIGH RISK weekend for fire blight infection in all areas – monitor individual situations closely and stay alert for precipitation forecasts.
Friday, March 16, 2012
Dave Ritchie
Plant Pathology Extension
I will be providing fire blight risk forecasts at least once a week through the bloom period based on the MaryBlyt model. If you wish to download and run the model for your specific location, it is available for no cost at www.caf.wvu.edu/kearneysville/maryblyt/.
Weather data will be from “weatherunderground”. I will be using a station in the Edneyville area of Henderson County (elevation 2205 ft), Columbus in Polk County (elevation 1066 ft), and Hickory Airport (elevation 1180 ft). Bill Hanlin informed me that he will run the model for the Wilkes and Alexander areas, thus I will not be providing forecasts for that area.
I will use weather conditions through the current date that I send you a forecast and PROJECT fire blight risk forward based on weather forecasts for the next 5 to 7 days. Please be aware that this 5 to 7 day risk projection is based on predicated weather conditions that can (probably will) change.
FIRE BLIGHT RISK AS OF 16 MARCH 2012 ---
I ran MaryBlyt this afternoon using several scenarios and here is what the model predicts through Thursday, March 22. I only ran it for Polk and Henderson Counties. I suspect that Hickory Airport conditions would be fairly similar to weather conditions from Columbus in Polk County.
POLK COUNTY: Assuming growth stage as tight cluster or pink with no blooms open and rainfall – NO RISK. However, running the model with the blossoms open and at least 0.05 inches of rainfall, the risk for blossom blight is HIGH and if rainfall continues INFECTION is predicated. If rainfall is 0.01 inches, the risk is HIGH, but infection is not predicted.
HENDERSON COUNTY: Assuming growth stage as tight cluster or pink with no blooms open and rainfall – NO RISK. Running the model with the blossoms open and at least 0.05 inches of rainfall, the risk for blossom blight is HIGH. However, with continued rainfall the model does not predict infection based on predicted temperatures because accumulated heat has not been met.
My conclusions for both areas, once blossoms open and rainfall with sufficient wetting occurs, the risk for infection becomes high. I will run the model early next week, taking into account weather conditions between now and then.
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