Extended wetting September 12 to 19

This past week we had wetting periods of 12 hr Sept 12-13, 18 hr Sept 14-15, 13 hr Sept 16-17 and 11 hr Sept 17-18; total rainfall for the week was 0.74 in. Total wetting hours last week was 58 which brought us to 768 total accumulated wetting hours, more than 200 hr ahead of last year.

Lee's left-overs

Tropical storm Lee brought us rainfall that totaled 2.72 inches over several days, Sept. 4-7. The ground seemed to soak up this volume of rain surprisingly well, and it will be beneficial for sizing the apple crop. Of course this amount of rain and the extended wetting should be expected to have some consequences for disease development, particularly if fungicide residues were low. Keep watching for sooty blotch and flyspeck, as well for as fruit rots such as bitter rot.

For the record, we had extended wetting periods of 16 hr Sept 4-5 at 69º F, 47 hr Sept 5-7 at 69º F, 12 hr at 64º F Sept 7-8 with Lee, and a more recent one of 22 hr at 68º degrees. Generally, wetting in the higher temperature ranges favor more rapid rot infection and development, and ripening fruit are more susceptible to infection. Typically, residues of a protectant fungicide such as captan do not weather through more than two inches of rainfall in a one week period.

Effects of Hurricane Irene

Considering the lack of rainfall the past three months, Irene's effects in the vicinity of our AREC were mostly beneficial; we received 1.2 inches of rain. The longest continuous wetting period during the weekend was 12 hr, but there were numerous showers earlier, all with temperatures in the 70s, and favorable for rot development. In spite of earlier drought, we have been seeing a lot of bitter rot in our fungicide test plots, a caution to commercial processing orchards with light fungicide programs.

Last week's total for wetting hours was 34, giving us 542 accumulated wetting hours for the season.

Strong winds resulted in some fruit drop of cultivars that won't be ripe for a month, but it was interesting to note that ripening Gala apples, treated with Fruitone (NAA "stop-drop") on Aug 15, held on nicely.

Extended wetting periods and accumulated wetting hours

We have had the following additional extended wetting periods in August:
Aug 6-7; 15 hours at 74º  with 0.85" rainfall.
Aug 13-14; 12 hours at 69º with 0.01" of rain.
Aug 14-15; 14 hours at 67º with 0.18" rainfall.
 
As of today we have reached 491 accumulated wetting hours- almost twice the threshold for development of sooty blotch and flyspeck. This is running about 70 hours ahead of this time last year.
 
We are observing sooty blotch and flyspeck and bitter rot on poorly protected apple trees.

Last week we accumulated an additional 16 wetting hours which brings us to a total of 360 hours, 110 hr past the 250-hour action threshold for development of sooty blotch and flyspeck on unprotected fruit. Total rainfall for the week was 0.22 inches.

Below is a picture of brown rot on Klondike White peach, taken last week. The dieback of shoots indicates high susceptibility of this cultivar, similar to what we have occasionally seen on Redgold nectarine. Klondike White is also very susceptible to bacterial spot. In this case the brown rot infection was probably initiated by hail injury followed by cracking of the fruit with increased growth. At our AREC, brown rot pressure has not been unusually high yet this year but this does not bode well for this local situation, and removal of early infected fruit might be beneficial to prevent spread to later ripening cultivars.

Summer disease pressures

Last week we accumulated an additional 58 wetting hours to brinus to a total of 344 hours, 94 hr past the 250-hour action threshold for development of sooty blotch and flyspeck on unprotected fruit. There was an extended wetting periods with rain July 8-9 (8 hr at 69º). Total rainfall for the week at our AREC was 0.42 inches.

Summer diseases

Extended wetting last night, July 7-8:  8 hr at 70º with 0.15 in. rain. Consider wetting periods 70º and above to be more favorable for rot diseases, especially bitter rot.

Sooty blotch and flyspeck

Sooty blotch symptoms were observed on unprotected fruit at our AREC July 5, with symptoms probably appearing in lower areas of the farm late last week.

Last week we accumulated 26 hours of wetting from rain and dew, bringing us to a total of 288 hours, 38 hr past the 250-hour action threshold for development of sooty blotch and flyspeck on unprotected fruit. There were two extended wetting periods from rain in the last week: June 27 (11 hr at 67º with 0.05 in. rain) and July 4-5 (14 hr at 84-66º with only 0.01 in. rain at our AREC, but with lightning to the north of Winchester as a backdrop for the fireworks display).  The last two nights brought an additional accumulation of 16 wetting hours from dew.

Wetting hour accumulation from dew may be more likely in lower areas, while wetting from rain will probably affect higher and lower elevations in an orchard more uniformly. Typically, symptoms appear earlier in lower areas but it is prudent to begin scouting for symptoms in those areas most likely to show symptoms, whether because of low elevation or lack of recent fungicide protection.

Appearance of sooty blotch/flyspeck symptoms probably also indicate a lack of fungicide residue to effectively control rot development. Where present, fire blight-killed shoots should be viewed as a potential fruit rot inoculum source.

Summer disease update

Last week we accumlated 34 hours of wetting from rain and dew. This brings us to a total of 262 hours, surpassing the 250-hour action threshold for development of sooty blotch and flyspeck on unprotected fruit. This is about the same time we reached the threshold last year.

Summer disease update

Over the weekend we got some much needed rain, totaling 1.8 inches for June 18-20. We had two extended wetting periods: 17 hr at 72 F June 18-19 and 12 hr at 70 F June 19-20. Last week we accumlated 40 hours of wetting, mostly from rain. This brings us to a total of 228 hours toward the 250-hour action threshold for sooty blotch and flyspeck.

Accumulated wetting hours

Last week we had 34 hours wet, mostly from dew. This gives us a total of 188 hours toward the 250-hour threshold.

Rappahannock County (Washington, VA) had 209 wetting hours as of June 8, and probably will reach the 250-hr threshold for development of sooty blotch and flyspeck on unprotected fruit this week.

Accumulated wetting hours

Last week we had 11 hours of wetting, bringing us to a total of 154 accumulated hours at our AREC.

This year we had 28 dry weather "mildew infection days" in April-May compared to 45 last year, but secondary mildew symptoms are common where control was not adequate. Control is still advised where shoot growth is continuing. Over the 18-year period that we have recorded this, the number of "mildew days in April-May has ranged from 24 to 49.

Extended wetting and accumulated wetting hours.

Extended wetting periods, favorable for secondary scab infection, occurred with light rains May 27 and 28, with 7 and 8 hr wetting, respectively. There were 34 total wetting hours last week, bringing the year's total since May 8 to 143 hr. The action threshold for sooty blotch and flyspeck is 250 wetting hours.

Wetting period, hail and trauma blight prediction, and sooty blotch/flyspeck wetting hours

Last night we recorded an apple scab infection period (8 hr wet, mean 67°F).

Last Tuesday afternoon, May 17, scattered hail occurred with 1.6” of rain in some areas of Frederick County. Tracking Maryblyt prediction for this single event with this week's highs in the mid-80s and lows in the mid-60s, indicates that trauma blight symptoms should begin to appear May 25. Typically trauma blight is more common in affected areas that also had some blossom blight from infection during bloom. The plant growth regulator, Apogee, applied at petal fall on king bloom, helps to reduce the amount of shoot tip infection (shoot blight) in these situations.

Since May 8 we now have accumulated 109 hr toward the 250 wetting hour threshold for specific treatment against the sooty blotch and flyspeck fungal complex.

Wetting periods May 17-19.

We recorded two scab and cedar-apple rust infection periods: May 17-18 (12 hr, 60°, 0.12" rain) and May 18-19 (15 hr, 60-51°, 0.04' rain). This makes seven infection periods and 3.89 inches of rain in the last week.

Scab and cedar rust infection period

As of 6 PM today, it has been wet 20 hr since last evening at temperatures around 60°F, we have had 2.2 inches of rain since yesterday, and it doesn't look like it is done yet. The best that we can say is that this long wetting period may wear out most of the cedar-apple rust galls, although there still was inoculum available for this one.

Weekend scab and rust infection periods

We recorded three scab and cedar-apple rust infection periods since Friday evening, May 13 (actually each of the last four nights): May 13-14 (14 hr, 63°), May 14-15 (14 hr, 63°), and May 15-16 (17 hr, 64-56°). Total rainfall for these three infection periods was 1.2". All of these were favorable for cedar-apple rust on foliage and rust inoculum is still available. Most fruit were no longer susceptible to quince rust.  These four consecutive infection periods pose a serious secondary scab threat and, because of the difficulty maintaining good spray coverage earlier, it will be important to scout orchards carefully for scab the next week or two to ensure clean fruit.


Since May 8 we now have accumulated 55 hr toward the 250 wetting hour threshold for specific treatment against the sooty blotch and flyspeck fungal complex.

Scab and rust infection period and start of sooty blotch and flyspeck development

An apple scab and cedar-apple rust infection period occurred last night and today, with 14 hr wetting at 63° F, and 0.4 inch rainfall.


For purposes of predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours, starting 10 days after petal fall. This year’s petal fall date was April 28 so the start of wetting hour accumulation will be from May 8. This is nine days later than last year’s start date. Today's infection period represents 14 wetting hours accumulated toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex.

2011 fire blight wrap-up (we hope)

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making management decisions outside of that area is not advised. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.



FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most apple cultivars are past petal fall but some still have scattered late bloom. The temperature and wetting data are current through Monday morning, May 6. Predicted weather conditions are shown for May 9-14. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection could have occurred last Friday, May 6, and again where late bloom persists, May 13. Actually, after tomorrow, infection could occur anywhere that late bloom remains and wetting occurs each day this week. Be aware that wetting by a fruit thinning or maintenance spray can result in infection if susceptible blossoms are available. Streptomycin should be included in such applications if all infection criteria are met except wetting. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. With five consecutive days possible for infection Apr 24-28, we have seen the most sustained fire blight pressure since 2004, and some infection will be expected in commercial orchards.

The BBS column is tracking predicted blossom blight symptoms from the first ten infection periods starting Apr 11 as “a”, then Apr 14, 20 and 24-28 as b-h. Some blossom cluster symptoms might be appearing now in local orchards. Growers are advised to protect high-risk blocks through late bloom as needed. The CBS column predicts that canker blight symptoms on new growth, due to extension of overwintering cankers from last year, will begin to appear May 11. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms indicates a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc. Fire blight cankers should also be recognized as a warning for potential fruit rot problems later in the season; bitter rot (Colletotrichum spp.) spores can be produced on blight-killed twigs and spurs within six weeks after the initial fire blight infection.

With only late bloom remaining, this will be the last Maryblyt graphic update for this season. The weather conditions used in the predictive part of this graphic came from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fire blight update, May 6

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most apple cultivars have reached petal fall but some have scattered bloom, and Yorks and Romes are at late bloom. The temperature and wetting data are current through Friday morning, May 6. Predicted weather conditions are shown for May 6-9. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Based on predicted temperatures and wetting, the risk column shows that, with slightly warmer than predicted temperatures and wetting, fire blight infection could occur today, May 6. Also, be aware that wetting can occur with a fruit thinning application. Streptomycin should be included in such applications if late bloom is present and all infection criteria are met except wetting. With five consecutive days possible for infection Apr 24-28, we have seen the most sustained fire blight pressure since 2004, and some infection will be expected in commercial orchards. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a-f) and canker blight symptom appearance, respectively. Some early blossom cluster symptoms might be starting to appear in orchards. Flower cluster leaf infection was reported May 3 in central Virginia. With this year’s disease pressure, you may want to consider applying the plant growth regulator, Apogee as a shoot blight suppressant. Optimum timing of the first Apogee application for this purpose is at petal fall on king bloom, and a suppressive effect should not be expected until 7-10 after Apogee application. Growers are advised to be alert to changes in forecasts on a day to day basis and protect high-risk blocks through late bloom as needed. This graphic will be updated May 9. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Scab, rusts and fire blight update, May 4.

An apple scab and rust infection period occurred last night; 16-hr wetting at 75-42° F, with 0.4 inch rainfall. Fruit infection by quince rust and cedar-apple rust was observed today at our AREC likely from infection that occurred Apr 16.

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most apple cultivars have reached petal fall but still with scattered bloom, and others, such as Yorks and Romes, are still have a lot of susceptible bloom. The temperature and wetting data are current through Wednesday morning, May 4. Predicted weather conditions are shown for May 4-8. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection could have occurred as predicted, May 3 (note red color in BHWTR column) and could also occur with slightly warmer than predicted temperatures and wetting May 5. Be aware that wetting can occur with a fruit thinning application. Streptomycin should be included in such applications if all infection criteria are met except wetting. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. With five consecutive days possible for infection Apr 24-28, we have seen the most sustained fire blight pressure since 2004, and some infection will be expected in commercial orchards. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a-e) and canker blight symptom appearance, respectively. The column labeled SBS is tracking the appearance of shoot blight symptoms. Some early blossom cluster symptoms might be starting to appear in orchards. We are now seeing blossom symptoms from experimental inoculations done at our AREC Apr 23. Flower cluster infection was reported yesterday in central Virginia. With this year’s disease pressure, you may want to consider applying the plant growth regulator, Apogee as a shoot blight suppressant. Optimum timing of the first Apogee application for this purpose is at petal fall on king bloom, and a suppressive effect would not be expected until 7-10 after Apogee application. Growers are advised to be alert to changes in forecasts on a day to day basis and protect high-risk blocks through late bloom as needed. This Maryblyt graphic will be updated May 6. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fungal disease update

Sixteen hours of intermittent wetting May 1-2 favored primary and secondary apple scab infection of leaves and fruit, quince rust fruit infection on cultivars in bloom and cedar-apple rust on foliage of all susceptible cultivars. Because a lot of rust inoculum was still available for infection during this wetting, it would be prudent to include an SI fungicide for after-infection rust control in applications this week. On stone fruits, these weather conditions were also favorable for peach scab and cherry leaf spot infection.

Since primary apple powdery mildew inoculum was first observed March 23, 13 dry-weather days have been favorable for mildew infection. Although this is fewer mildew days than we had to this point last year, secondary mildew lesions will become apparent on new growth in affected blocks.

Fire blight- we're not out of the woods yet...

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Some apple cultivars have reached petal fall but others still have scattered bloom, and others, such as Yorks and Romes, are still very susceptible. (The Yorks hung around for visitors to the Apple Blossom Festival this year). The temperature and wetting data are current through Monday morning, May 2. Predicted weather conditions are shown for May 2-5. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection is again possible with wetting tomorrow, May 3 (note red color in BHWTR column). Be aware that wetting can occur with a fruit thinning or other application. Streptomycin should be included in such applications on days when all infection criteria are met except wetting. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. With five consecutive days possible for infection Apr 24-28, we have seen the most sustained fire blight pressure since 2004, and some infection will be expected in commercial orchards. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a-e) and canker blight symptom appearance, respectively. The column labeled SBS is tracking the appearance of shoot blight symptoms. Some early blossom cluster symptoms might be starting to appear in orchards. We are now seeing blossom symptoms from experimental inoculations done at our AREC Apr 23. With this year’s disease pressure, you may want to consider applying the plant growth regulator, Apogee as a shoot blight suppressant. Optimum timing of the first Apogee application for this purpose is at petal fall on king bloom, and a suppressive effect would not be expected until 7-10 after Apogee application. Note that risks can increase quickly with unpredicted wetting and warmer than predicted temperatures. Growers are advised to be alert to changes in forecasts on a day to day basis and protect high-risk blocks through late bloom as needed. This graphic will not be updated until May 4. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fungal disease and fire blight update

Primary apple scab lesions were observed today on unprotected trees at our AREC. Size and positions of infected leaves and appearance of lesions suggest that some could have been from infection Mar 30-Apr 1 and some from Apr 8-9. It is likely that they were present during infection periods Apr 22-23 and Apr 24-25 and, as such, could have provided secondary inoculum for heavy fruit infection in poorly protected orchards. Last night's wetting with 1.7 inches of rain was not quite long enough for scab or rust infection, but the 11-hr wetting event at 60-69° F Apr 24-25 favored quince rust of blossoms and cedar-apple rust infection of leaves and fruit, as well as scab. Quince and rust gall inoculum is still available on the cedar trees in our area.

Since primary powdery mildew inoculum was first observed Mar 23, eleven dry weather days have been favorable for mildew infection.

FIRE BLIGHT CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Some apple trees have reached petal fall but others still have much bloom still open and susceptible. Late cultivars such as Rome and York may be near full bloom. The temperature and wetting data are current through Thursday morning, April 28. Predicted weather conditions are shown for April 28-May 2. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection is possible with rainfall today, Apr 28 (note red color) and would again be possible if wetting were to occur Apr 29-30. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. This year’s bloom season has seen considerable sustained fire blight pressure and some infection will be expected in commercial orchards. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a, c and d) and canker blight symptom appearance, respectively. Numbers in these columns represent percent of required degree hours for early blossom symptom appearance and canker margin symptoms Apr 26. Today, early symptoms are evident from experimental inoculations done Apr 23. Today’s update was a result of changes in the weather forecast from yesterday. RISKS CAN INCREASE QUICKLY WITH WETTING FOLLOWING WARMER THAN PREDICTED TEMPERATURES. Growers are advised to be alert to changes in forecasts on a day to day basis and protect high-risk blocks through late bloom as needed. This graphic will not be updated until May 2 unless some significant change warrants it. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fire blight Apr 27

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Many apple trees are now near petal fall but with much bloom still open and susceptible. Late cultivars such as Rome are at full bloom. The temperature and wetting data are current through Wednesday morning, April 27. Predicted weather conditions are shown for April 27-May 2. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection is possible with rainfall today and tomorrow, Apr 28 and would again be possible if wetting were to occur Apr 30-May 2 (note red color). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. This bloom season has seen some sustained fire blight pressure. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. This graphic will be updated April 29, or sooner if significant change warrants it. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a, c and d) and canker blight symptom appearance, respectively. Numbers in these columns represent percent of required degree hours for early blossom symptom appearance and canker margin symptoms Apr 26. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fire blight update Apr 25.

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

 

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Many apple trees are now near full bloom or approaching petal fall but with much bloom still open and susceptible. The temperature and wetting data are current through Monday morning, April 25. Predicted weather conditions are shown for April 25-30. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection is possible with rainfall each day this week through Apr 28 (note red color). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Although temperatures will decline slightly Apr 29-30, risk will remain at an infective level if wetting occurs. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. This graphic will be updated April 27, or sooner if significant change warrants it. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a and c) and canker blight symptom appearance, respectively. Numbers in these columns represent percent of required degree hours for early blossom symptom appearance and canker margin symptoms Apr 26. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fire blight outlook April 24

FIRE BLIGHT!  The Maryblyt prediction will be updated with actual recorded temperatures tomorrow morning, but temperatures through the weekend and the forecast through Apr 27 are similar to what was shown in the Maryblyt graphic below, posted Apr 22. There was a threat of fire blight infection anywhere that had rain in the Winchester area today.

The wetting period Apr 22-23 was likely too cool for quince rust infection, but temperatures last night and tonight are more favorable and blossoms are near their peak of susceptibility.

Scab infection period Apr 22-23

Wet 25 hr at 42-46°, this would result in a serious secondary infection period where scab lesions are already present in trees that were not adequately protected during the first primary period Mar 30-Apr 1.

Fire blight update

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

Maryblyt graphic. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Many apple trees are now near full bloom, and more bloom will continue to open over the next several days. The temperature and rainfall data are current through Friday morning, April 22. Predicted weather conditions are shown for April 22-27. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection is possible with rainfall later today Apr 20 (note red color). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Following today’s cool temperatures risk will again begin to increase and reach an infective level if it rains any of the days, Apr 24-27. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. An application tomorrow should protect nearly through this long high-risk period. This graphic will be updated April 25, or sooner if significant change warrants it. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11) and canker blight symptom appearance, respectively. Numbers in these columns represent percent of required degree hours leading to blossom symptom appearance Apr 26 and canker margin symptoms Apr 27. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fire blight update and scab infection, Apr. 20

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Earlier apple cultivars are approaching full bloom open, late ones have some bloom open, and more bloom will open over the several days. The temperature and rainfall data are current through Wednesday morning, April 20. Predicted weather conditions are shown for April 20-24. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that fire blight infection is possible if it rains later today, Apr 20 (note red color). (UPDATE Apr 21: We did not have the wetting from rainfall required for fire blight infection at the AREC yesterday; however, on a day when all the other requirements are met, wetting by a spray application can initiate infection). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Following today’s potential infection, risk will subside with cooler temperatures but will again reach an infective level with rain Sunday, Apr 24. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. An application today should protect for both of these high-risk periods. This graphic will be updated April 22, or sooner if significant change warrants it. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11) and canker blight symptom appearance, respectively. The numbers in these columns represent percent of required degree hours for symptom appearance. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Length of wetting from 9 pm Apr 19- 8 am Apr 20 was just long enough for a scab infection period: 12 hr at 50-54F. There had been wetting earlier with 0.4 inches of rainfall on Apr 19 but that was not included because of 5-hr drying in the interim. Rusts, and especially quince rust, are still a threat, but rust-prone blocks covered with an SI fungicide would have been well-protected for this event.

Fire blight update

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Earlier cultivars have much bloom open, others are at full pink, and more bloom will open over the several days. The temperature and rainfall data are current through Monday evening, April 18. Predicted weather conditions are shown for April 18-25. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that risk of fire blight infection will again reach an infective level with warmer temperatures and rainfall Apr 20 (note red color). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. This graphic will be updated April 20, or sooner if significant change warrants it. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11) and canker blight symptom appearance, respectively. The numbers in these columns represent percent of required degree hours for symptom appearance. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Scab and rust infection period

An apple scab and possible cedar-apple and quince rust infection period was recorded with 20-hr wetting from 2 AM-10 PM Apr 16. Temperatures through the wetting period ranged from 47-58F at the AREC but were as much as 4 degrees warmer in Winchester. Blossoms are now highly susceptible to quince rust. The 1.8-in. rainfall would have depleted most of the residue of non-systemic protectant fungicides applied this week, but an SI fungicide applied Apr 14-15 would have controlled any rust infection that occurred in this wetting period as well as the one Apr 12-13.

Fire blight update

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Early cultivars have a lot of bloom open, others are at full pink, and more bloom will open gradually over the next two days. The temperature and rainfall data are current through Thursday evening, April 14. Predicted weather conditions are shown for April 15-22. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, the risk column shows that risk of fire blight infection will be low or moderate through Apr 19, but will again reach an infective level with warmer temperatures and rainfall Apr 20-21 (note red color). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. This graphic will be updated April 18, or sooner if significant change warrants it. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11) and canker blight symptom appearance, respectively. The numbers in these columns represent percent of required degree hours for symptom appearance.

 The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Scab and rust infection period Apr 12-13

We recorded 27 hr wetting with 1.6 in of rainfall from 6 AM Apr 12- 9 AM Apr 13 with the first 10 hr at 53, then gradually dropping to 49. This wetting was plenty long for an apple scab infection period and likely also an infection period for cedar-apple and quince rusts although it was a bit on the cool side for rusts. Rust spores were discharged during this wetting and blossoms are now susceptible to quince rust which results in distorted fruit at harvest. Quince rust inoculum is produced by cankers (shown below) that can survive for many years, resulting in consistently high local inoculum levels from year to year (to year). Because an inch and a half of rainfall would have eroded most of EBDC residue applied this week before the rain, a follow-up application including an SI fungicide is suggested for after-infection control. Strobilurin (QoI) fungicides are notably weak for quince rust control.

The fire blight graphic will be updated tomorrow. Temperatures yesterday and today have been too cool for fire blight infection, although infection could have occurred as predicted with the rain early Tuesday morning on bloom that was open Monday.

Quince rust inoculum source, a perennial canker in red cedar.

  

Two-celled quince rust teliospores germinating in the exuding mass (click on the picture to enlarge it). Orange-colored ones have not yet germinated but those that are clear have germinated and the resulting basidiospores (the smaller, more rounded ones, top, center above) are carried away by wind currents.

Fire blight loomin' where trees are bloomin'

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Although early cultivars are approaching pink with occasional blossoms open, with warmer temperatures, more bloom will be open later today. With warm temperatures and evening rain predicted for today, I ran Maryblyt as an indication of risk in locations where some bloom (including pollinizer crabapples) is open this morning April 11, 2011. The temperature and rainfall data are current through Sunday evening, April 10. Predicted weather conditions are shown for April 11-12. The components of fire blight risk are indicated in the columns labeled BHWTR with B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, The risk column shows that fire blight infection (I) is possible with predicted rain tonight, April 11 (note red color). For infection to be predicted, wetting has to occur after the EIP (epiphytic infection potential) reaches 100 or higher. Briefly put, bloom that is open today is at risk for infection if wetting occurs tonight. A streptomycin application is recommended for high risk situations. Today’s forecast represents a high risk situation for areas farther south and east of the Blue Ridge with much bloom open, in some cases for a week. For the Winchester area, the current longer-range outlook indicates cool temperatures April 12-19, so risk will subside after today. This graphic will be updated April 13. The BBS and CBS columns are tracking predicted blossom blight symptom and canker blight symptom appearance, respectively. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from Skybit, Inc.

Scab infection Apr 8-9.

A scab infection period was recorded at our AREC from 6 AM Apr 8-11 AM Apr 9. This included some intermittent wetting and temperatures ranging from 46-39F with approximately 0.3 in rainfall.

For the record, wetting at our AREC Apr 4-5 was not adequate for scab infection and few cedar-apple rust spores have been released to date.

Scab infection

A scab infection period was recorded with wetting from 3:30 PM Mar 30- 8 AM Apr 1. Intermittent wetting/drying occurred mid-day Mar 31 but it is likely that most local areas did not have enough drying to stop the infection process. This is the first scab infection period of the season at our AREC.

Reminder- meeting tonight

This is a reminder that tonight is our first In-Depth Meeting of the year, 7:00 – 8:30 p.m at our AREC. Following Chris Bergh’s entomology update, I will discuss Early Season Apple Disease Management and Positioning of Newer Fungicides. Pathology updates will be included in the discussion.

Please note these additional dates for meetings at our AREC:

Thursday, April 14: Breakfast Meeting 7:00 – 8:00 a.m. Pathology, Entomology and Horticulture updates and breakfast provided.
Following this meeting, at 8:30 AM, a memorial tree and stone plaque will be dedicated in memory of horticulturist, Dr. Rongcai Yuan, on the anniversary of his passing last year.

Thursday, April 28: In-Depth Meeting 7:00 – 8:30 p.m. Pathology, Entomology and Horticulture updates. Fruit Thinning discussion with Drs. Greg Peck and Steve Miller.

Thursday, May 12: Breakfast Meeting 7:00 – 8:00 a.m. Pathology, Entomology and Horticulture updates and breakfast provided.

Thursday, June 2: In-Depth Meeting 7:00 – 8:30 p.m. Pathology, Entomology and Horticulture updates; and Speaker/topic to be announced.

Can we get scab infection with snow?

The really unusual weather we've had so far this spring, and a forecast for who knows what the next two days or so, brings up the old question about whether it is possible to have an apple scab infection period with wetting by melting snow. The answer, of course is, yes it is. If there is enough wetting to initiate ascospore discharge and deposition on susceptible tissue in the tree, then prolonged wetting from melting snow (48 hr at near freezing temperatures) can result in infection. We saw it happen in 1990- a year that gave us three snows and 13 nights below freezing after green tip - and we still ended up with decent apple and peach crops.  Logic says that if the snow blankets frozen ground before ascospore discharge, it would prevent discharge into the air, negating impaction of the ascospores in the tree and therefore would not result in infection.

Speaking of the wild weather this spring, without looking back, I don't recall a year when we had this much prolonged cold after green tip. So far, at the AREC, we see only a little damage of king bloom that was showing some color (a little bit beyond tight cluster) Sunday morning when the temperature dipped to 26. The coldest time seemed to come with the snow and there was probably air movement that brought cold to higher elevations in the orchard blocks that were more advanced than lower areas (a freeze rather than a frost). Once we get through this, hopefully the week or more of colder weather will be recognized as having been beneficial because it delayed bud and reduced susceptibility to later frosts.

Wetting March 23-24

At our AREC we recorded wetting from 7:15 PM Mar 23 - 10:30 AM Mar 24, about 85% of the duration of wetting required for scab infection at temperatures that ranged from 49F down to 37F. But temperatures and area showers were variable earlier on March 23 and some local areas may have had their first scab infection. Wetting occurred north of Winchester by 6 PM while the temperature was at 55F; other areas had showers near noon March 23 and may have remained wet longer. Scab protectants applied before this wetting probably weathered through the rainfall which totaled about half an inch. At our AREC, apple bud stage varies from 1/2"- green for York (shown above) and Rome to tight cluster for several cultivars including Gala, Red Delicious and Idared. Where no fungicides have been applied and length of wetting is marginal or in doubt, it would be prudent to include one with after-infection control in the first application. Also, consider that powdery mildew spores are now available for infection during dry weather 53F and higher, and cedar-apple rust gall spore horns are extended to more than a half-inch, indicating potential for rust infection with the next rain in the mid-50s and higher.

Apple powdery mildew

Today Idared apples were at tight cluster with some petal color showing through as seen in the first picture below. The second picture shows a healthy bud on the left and a reddish, mildewed bud on the right. Although much of the exposed surfaces appeared to have been "washed off" by recent rains, as suspected there were abundant mildew spores (conidia) present on the more protected surfaces (last picture). Cool, damp weather is more conducive to scab development than mildew but it is obvious that spores will plentiful when the temperature turns warmer again (53F+).

Apple bud stage March 21

This morning nearly all apple cultivars at our AREC were showing some green. Above is the same Red Delicious bud that I pictured last Thursday. (The dark brown vertical structure is a leaf petiole hanging on from last year). Red Delicious fruit buds are at or near 1/2-inch green. Idared is a little more advanced with some cluster leaves curling back as they do for tight cluster stage.

The thunderstorm this morning gave us 0.45 inch of rain but it wasn't wet long enough for scab infection. Showers are forecasted again for this evening and tomorrow evening.

Outlook for next week

This year is starting out reminiscent of last year when we caught some apple scab spores and then had an infection period several days later.  A protectant spray of copper, mancozeb, or ziram before that first infection period and later protectants would have greatly diminished the threat of scab through much of April, but a delayed application after the first infection period required something with some after-infection control to prevent the appearance of lesions and re-infection two weeks later.

A chance of showers from tomorrow evening (Sunday, Mar 20) through Monday evening at temperatures in the mid-40s and warmer could again lead to early infection, assuming that most blocks in the Frederick County are not yet covered with a fungicide. In case there is an infection period, remember that follow-up sprays of copper or an EBDC fungicide alone do not have after-infection control. We have found that Vangard can be tank-mixed with copper or mancozeb to improve after-infection control in these early season situations.

We have applied oil to most of our fungicide test blocks in anticipation of increased mite populations later in the season if we need to step up controls for Brown Marmorated Stink Bug (BMSB). Remember to leave 7-14 days between an oil spray and sprays of captan or sulfur. We did not apply oil to the Red Delicious fungicide blocks to see if increased mite populations will aggravate the Alternaria Leaf Blotch that causes defoliation of Red Delicious, that has been observed for several years and might reappear this year.

It's a new season!

Apple scab ascospores were trapped during rains March 15-16. Red Delicious and Idared cultivars were showing some early greentip at our AREC the morning of March 16 but the 18-hr wetting was not long enough for infection at mean temperature 40° F.



Red Delicious fruit bud 3-17-11