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.