Disease update: quince rust, powdery mildew, and fire blight

Quince rust lesions (shown on fruits below) are appearing this week from infections that occurred on unprotected fruit Apr 28-May 1.

Early quince rust symptoms. Photo by Allen Cochran May 19, 2014

Powdery mildew:   We have had 27 dry weather “mildew infection days” since spores first became available Apr 9. With good soil moisture and warmer temperatures, expect continued susceptibility of new growth for some time.

Fire blight: Predicted risk remains at an infective level wherever bloom remains and wetting occurs. Pay particular attention to newly planted trees which may have susceptible blossoms.

Scab and rust infection; heavy rainfall, May 15-16

We recorded 16 hours of wetting at 67-54° with 2.9 inches of rain at our AREC May 15-16. This was a secondary apple scab, cedar-apple rust infection period, and quince rust infection period, especially for later blooming cultivars. This amount of rainfall likely eliminated most of the protective fungicide residue on leaves and fruit, and puts more selective pressure on fungicides that are "at risk" for development of resistance in the apple scab fungus. 

Where protection was not adequate, growers are advised to follow up with a tank-mix of fungicides with multiple modes for scab, and an SI fungicide to offset possible infection of blossoms by quince rust. A protective fungicide should be included in this mix. Similar conditions occurred in central Virginia, where 4.2 inches of rainfall was recorded at Tyro.

Powdery mildew spores were available under the dry weather conditions favorable for infection Apr 9, and we have had 22 dry weather “mildew infection days” since Apr 9.

Fire blight: Predicted risk of fire blight has diminished for today through the weekend to May 20 when it will again increase to an infective level where lingering bloom remains.

Fire blight update; scab and rust infection

The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment for the area of the Virginia Tech AREC located six miles southwest of Winchester. At our AREC there is still a lot of susceptible bloom on late blooming cultivars such as Rome. 

FIRE BLIGHT ALERT: The risk column of Maryblyt 7 graphic below, based on predicted temperatures and wetting for May 14-18, shows that fire blight risk will remain extremely high through Friday, May 16 wherever bloom is present. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions. In the event of hail injury or other trauma blight situation, apply streptomycin as soon as possible after the event. Routine spray applications can provide enough wetting to meet the wetting requirement for infection if all other infection conditions have been met and this would have been true for May 11-12. Under the warm temperature conditions shown for the this week, streptomycin remains residually effective for only about 3 days. 

With this fire blight pressure, you still might want to consider applying the plant growth regulator, Apogee to suppress shoot blight if hail or another trauma blight event were to occur. 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.

The temperature and rainfall data are current through Wednesday morning, May 14, for the graphic above from the Maryblyt 7 program. Predicted weather conditions are shown for May 12-16. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial population buildup, EIP >100), W (wetting by rain or dew), and T (average daily temperature 60 F or above).  

The BBS column is tracking predicted appearance of blossom blight symptoms from infection May 8 to predicted symptom appearance (108a) May 14. The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, with canker margin symptoms (CMS) by May 8 and canker blight symptoms May 14. Canker advancement cannot be prevented by a chemical treatment, and the presence of symptoms will indicate a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc. 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 RUSTS: An apple scab and rust infection period is in progress, with more than 14 hr of wetting and temperatures in the mid-60s. Much cedar-apple and quince rust inoculum is still available and many small unprotected fruits are still susceptible. We are now into a heavy secondary scab situation where scab was not adequately controlled on Apr 11-12, Apr 14-15, or Apr 28-May 1. This wetting period also favors infection by peach scab.

Fire blight update

The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment for the area of the Virginia Tech AREC located six miles southwest of Winchester. At our AREC most apple cultivars still have scattered bloom and later blooming cultivars have much susceptible bloom. 

FIRE BLIGHT ALERT: The risk column of Maryblyt 7 graphic below, based on predicted temperatures and wetting for May 12-16, shows that fire blight risk will remain extremely high wherever bloom is present this week. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions. Routine spray applications can provide enough wetting to meet the wetting requirement for infection if all other infection conditions have been met. Under the warm temperature conditions shown for the this week, streptomycin remains residually effective for only about 3 days.

With this fire blight pressure, consider applying the plant growth regulator, Apogee to suppress shoot blight if hail or another trauma blight event were to occur. 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.

The temperature and rainfall data are current through Monday morning, May 12, for the graphic above from the Maryblyt 7 program. Predicted weather conditions are shown for May 12-16. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial population buildup, EIP >100), W (wetting by rain or dew), and T (average daily temperature 60 F or above).  

The BBS column is tracking predicted appearance of blossom blight symptoms from infection May 8 to predicted symptom appearance (104a) May 14. The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, with canker margin symptoms (CMS) by May 8 and canker blight symptoms May 14. Canker advancement cannot be prevented by a chemical treatment, and the presence of symptoms will indicate a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc. 

This graphic will be updated May 14. 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.

RUSTS: Today we observed scattered cedar-apple lesions on unprotected, frost-injured leaves from the infection period Apr 14-15, and many developing lesions from the long wetting period Apr 28- May 1. That infection period will also likely result in quince rust on unprotected fruit as the fruit begin to grow.

Continued fire blight threat

The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment for the area of the Virginia Tech AREC located six miles southwest of Winchester. At our AREC most apple cultivars still have some susceptible bloom and later blooming cultivars are near full bloom. 

FIRE BLIGHT ALERT: The risk column of Maryblyt 7 graphic below, based on predicted temperatures and wetting for May 9-14, shows that fire blight risk will remain extremely high for the next week May 8-15 (and later). In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions. Remember that routine spray applications can provide enough wetting to meet the wetting requirement for infection if all other infection conditions have been met. Under the warm temperature conditions shown for the next week, streptomycin remains residually effective for only about 3 days.

With fire blight pressure looming, you may want to consider applying the plant growth regulator, Apogee to suppress shoot blight if hail or another trauma blight event were to occur. Optimum timing of the first Apogee application for this purpose is at petal fall on king bloom, but a suppressive effect should not be expected until 7-10 after Apogee application.

The temperature and rainfall data are current through Friday morning, May 9, for the graphic above from the Maryblyt 7 program. Predicted weather conditions are shown for May 9-15. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial population buildup, EIP >100), W (wetting by rain or dew), and T (average daily temperature 60 F or above).  

The BBS column is tracking predicted appearance of blossom blight symptoms from infection May 8 to predicted symptoms (105a) May 15. The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, with canker margin symptoms (CMS) by May 8 and canker blight symptoms May 15. Canker advancement will not be prevented by a chemical treatment, and the presence of symptoms will indicate a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc. 

This graphic will be updated May 12. 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 alert

The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment for the area of the Virginia Tech AREC located six miles southwest of Winchester. At our AREC most apple cultivars still have some susceptible bloom and later blooming cultivars, such as Rome Beauty, are at full bloom. 

FIRE BLIGHT ALERT: The risk column of Maryblyt 7 graphic below, based on predicted temperatures and wetting for May 8-14, shows that fire blight risk will be extremely high for the next week, lacking only wetting for infection for May 12, and with predicted wetting, infection conditions are likely May 8-11 and 13-14. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions. Be aware that routine spray applications can provide enough wetting to meet the wetting requirement for infection when all other infection conditions have been met. Under the conditions shown for the next week, streptomycin remains residually effective for only about 3 days.

Above is a graphic from the Maryblyt 7 program. The temperature and rainfall data are current through Wednesday evening, May 7. Predicted weather conditions are shown for May 8-14. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial population buildup, EIP >100), W (wetting by rain or dew), and T (average daily temperature 60 F or above).  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.

Disease update: Fire blight risk high; apple scab lesions present

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. At our AREC most apple cultivars still have susceptible bloom, some are near full bloom and some have late bloom continuing to open. Later cultivars such as Rome Beauty are not yet at full bloom. 

FIRE BLIGHT: Above is a graphic from the Maryblyt 7 program. The temperature and rainfall data are current through this morning,  May 5. Predicted weather conditions are shown for May 5-14. 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 risk will be high, lacking only wetting for infection, for May 8-10 and with predicted wetting, infection conditions are likely May 11-14. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions, or with applications that cause wetting when all other infection conditions have been met. This graphic will be updated May 7. 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.

APPLE SCAB: Scab lesions, as shown below, were present at our AREC on May 2. As is quite common with appearance of the earliest primary scab, lesions may be somewhat obscured by necrotic frost injury which seemed to target the scab lesion. 

Primary scab lesion on Gala flower cluster leaf at right.

Lower leaf surface- note sporulation
outside of necrotic area

Primary scab symptom- necrotic area from
 frost injury on upper leaf surface

The abundance of conidiospores on the lesion indicated that they were likely present through last week's heavy infection period and would have contributed to heavy secondary infection on unprotected trees.

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. 

FIRE BLIGHT: Above is a graphic from the Maryblyt 7 program. Most apple cultivars at our AREC remain near full bloom, but with later blossoms continuing to open. Later cultivars such as Rome Beauty are not yet at full bloom. The temperature and rainfall data are current through this morning,  May 2. Predicted weather conditions are shown for May 2-11. 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 risk will be high, lacking only wetting for infection, for May 4. Risk then remains moderate to high or at an infective level through May 11.

CAUTION:  Be aware that risks can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions, or with applications that cause wetting when all other infection conditions have been met.This graphic will be updated May 5. 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.