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.