Some late season disease pressures

After enjoying some good harvest weather in September, with only 0.4 inches of rain in the Winchester area, the past two weeks have brought some significant late season disease pressures, but also with much needed rainfall. Extended wetting events occurred last week October 10-11 (27 hours at 55° with 0.4 inches of rain).  This week we had an extended wetting period of more than 60 hours with only intermittent drying Oct 14-17. Much of this was at relatively warm temperatures favorable for rots, including 9 hours at 71°. 

The most recent extended wetting, our longest since late April, also favored fruit scab infection wherever active scab was present in the orchard as a result of poor coverage or missed applications or fungicide resistance early in the season. Rainfall Oct 14-17 totaled more than 2.3 inches and likely depleted fungicide residue, even from applications in the past two weeks. This extended wetting at favorable temperatures was enough to cause "pin-point scab" (storage scab) of late cultivars, and early marketing (rather than long-term storage) is suggested for fruit from fresh-market orchards lacking recent fungicide protection where there was earlier evidence of active scab. 
  

Summer disease pressures: extended wetting and accumulated wetting hours

In the past two weeks we have had several extended wetting periods with rainfall, and more than 150 hours of wetting from rainfall or dew. Although the rainfall was not excessive, this amount of wetting at relatively warm temperatures does increase summer disease pressure considerably.

These were the extended wetting periods from rain at our AREC:
July 14-15, 19 hr with just 0.01 in. of rain at 73° (very favorable for rots).
July 18-19, 10 hr with 0.09 in. of rain at 68°.
July 19-20, 16 hr with just 0.04 in. of rain at 69°.
July 27, 11 hr with 0.39 in. of rain at 70° (also favorable for rots).
July 27-28, 12 hr with just 0.17 in. of rain at 69°.

We track the number of extending wetting periods above 70° as an indication of potential bitter rot weather. This is not an absolute cut-off temperature but gives a basis for year-to-year comparison of relative bitter rot pressure. Since June 1 this year we have had 13 such wetting periods while last year by this time we had only five.

 As of Monday morning, July 28, at our usual AREC monitoring site at elevation 950 ft, we had accumulated 440 wetting hours since May 18, well beyond the 250-hour threshold for specific treatment against the sooty blotch/flyspeck (SBFS) fungal complex . But at the 910 ft. elevation cumulative wetting hour (CWH) total continues to run about 100 ahead, now standing at 557 CWH. Sooty blotch/flyspeck symptoms (signs of the fungi) are now readily visible. Unprotected fruit that we collected about four week ago have now developed bitter rot as well as SBFS. 

Orchards at lower elevations in Nelson County (Tyro area) have greatly exceeded the 250-wetting hour threshold for presence of the SBFS organisms on unprotected fruit (total 475 CWH at 941 ft elevation). The CWH total at our highest monitoring location (elev. 1465 ft) stood at 272 CWH as of Monday morning, July 28; CWH accumulation at a middle elevation (1165 ft) has consistently lagged behind the other two and is now at 190 CWH. Scout lower areas of your orchards regularly for onset of SBFS appearance and adjust your fungicide program accordingly. 

Below is a picture of bitter rot on a Honeycrisp apple as seen in a commercial orchard in Nelson County June 26. Fruit mummy inoculum, such as that shown with this fruit, and inadequate spray coverage were likely factors that contributed to this problem, but it shows the importance of being vigilant to any and all possible developing problems.

Bitter rot on Honeycrisp apple fruit. Note the presence of small fruit mummies associated with the bitter rot problem.

Extended wetting for fruit rots July 8-9; accumulated wetting hours.

July 8-9 we had another extended wetting period: 15 hr with 0.24 in. of rain at 72°. This wetting period was favorable for rots.

As of Thursday morning, July 10, we had accumulated 293 wetting hours since May 18, well beyond the 250-hour threshold for specific treatment against the sooty blotch/flyspeck (SBFS) fungal complex at our usual AREC monitoring site at elevation 950 ft. But at the 910 ft. elevation cumulative wetting hour (CWH) total continues to run about 100 ahead, now standing at 391 CWH. Early sooty blotch symptoms (signs of the fungi) are now visible.  

Orchards at lower elevations in Nelson County (Tyro area) have also exceeded the 250-wetting hour threshold for presence of the SBFS organisms on unprotected fruit (total 345 CWH at 941 ft elevation). CWH total at the higher elevation stood at 200 CWH as of Thursday morning, July 10. Scout lower areas of your orchards regularly for onset of SBFS appearance and adjust your fungicide program accordingly.

Sooty blotch symptoms; extended wetting for fruit rots July 3-4.

Last week July 3-4 we had another extended wetting period: 9 hr with 0.6 in. of rain with a mean 71°. This wetting period was favorable for rots.

As of Monday morning, July 7, we had accumulated 270 wetting hours since May 18, well beyond the 250-hour threshold for specific treatment against the sooty blotch/flyspeck (SBFS) fungal complex at our usual AREC monitoring site at elevation 950 ft. But at the 910 ft. elevation we have recorded 372 CWH and early sooty blotch symptoms (signs of the fungi) are now visible.  

Orchards at lower elevations in Nelson County (Tyro area) have also exceeded the 250-wetting hour threshold for presence of the SBFS organisms on unprotected fruit. Scout your lower orchard areas regularly for onset of SBFS appearance and adjust your fungicide program accordingly.

Sooty blotch and flyspeck on unprotected fruit; rot infection period

Last night we had an extended wetting period following afternoon rains: 16 hr with 0.22 in. of rain at 75°. This wetting period was favorable for rots.

As of this morning, July 3, we had accumulated 258 wetting hours since May 18, surpassing the 250-hour threshold for specific treatment against the sooty blotch/flyspeck (SBFS) fungal complex at our usual AREC monitoring site at elevation 950 ft. This is the elevation from which we have reported cumulative wetting hours since 1994, and this is the latest we have reached that threshold since 1999. But we have recorded 352 CWH at a lower AREC site (elevation 910 ft).  

The wetting hour threshold indicates the time at which we would expect the SBFS organisms to be present, but not yet visible on unprotected fruit but we expect symptoms in the more advanced area shortly. Remember to scout your lower orchard areas regularly for onset of SBFS appearance and adjust your fungicide program accordingly.

Accumulated wetting hours for sooty blotch and flyspeck; mildew remains active; fire blight and rot inoculum levels.

 Each year we record accumulated wetting hours (CWH) from rainfall or dew, starting ten days after petal fall for purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex,. This past week wetting at our AREC occurred almost entirely as dew, with only traces of precipitation which dried quickly. 

As of yesterday morning, June 30, we had accumulated 228 wetting hours since May 18, approaching the 250-hour threshold for specific treatment against the SBFS fungal complex at our usual AREC monitoring site at elevation 950 ft. But at a lower AREC elevation (910 ft), we have greatly surpassed this threshold with 334 CWH.  Again this illustrates the importance of elevation for wetting hour accumulation. Remember to scout your lower orchard areas regularly for onset of SBFS appearance and adjust your fungicide program accordingly.

With the continued dry weather this past week, powdery mildew remains active where shoots are continuing to grow. Since mildew spores were first observed Apr 9, we have had 49 dry weather “mildew infection days”.

This past week in visits to Frederick County and central Virginia orchards, we saw more fire blight than we would like to see. This seemed to occur as a result of marginal protection at late bloom. For the most part, it does not appear to be spreading actively any more, but the presence of dead wood in the trees raises the concern of increased inoculum levels for the rot fungi, especially bitter rot, as we approach harvest. Bitter rot was already evident in one Nelson county orchard and small, over wintering fruit mummies seemed to the likely inoculum source in that situation.

Extended wetting events, mildew still active; wetting hour accumulation related to elevation

We had two more extended wetting events at our AREC this past week: June 16-17 (12 hr, mean 71° with 0.6 in. rain) and June 19-20 (14 hr, mean 71°, with 0.4 in. rain).

The temperatures and length of wetting during these events favored secondary apple scab and early summer disease development. Secondary spread of fire blight was possible where growing shoot tips are still susceptible. Cedar rust galls are mostly depleted now. 

Powdery mildew remains active with continued shoot growth. Since mildew spores were first observed Apr 9, we have had 42 dry weather “mildew infection days”: 15 in April, 20 in May and 7 in June. So it is not hard to find secondary infection in susceptible unprotected orchards.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (CWH) from rainfall or dew, starting May 18, ten days after petal fall. This week there was about twice as much wetting hour accumulation at Winchester than at the central Virginia location. 

By Friday morning, June 20, at our usual AREC monitoring site at elevation 950 ft, we had accumulated 176 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. But at a lower AREC elevation (910 ft) we have already surpassed this threshold with 289 CWH.  At Tyro, VA as of June 20, the sensor at 1165 ft. elevation had accumulated 99 wetting hours from May 11, while one placed at 941 ft had accumulated 193 hr. Both of these locations illustrate the importance of elevation for wetting hour accumulation. Scout your lower orchard areas for early onset of SBFS appearance and adjust you fungicide program accordingly.

Extended wetting events this week

It has been a wet week at our AREC this past week, with significant infection events five consecutive days, including the one noted in the previous post for June 8-9. These were as follows: June 9-10 (8 hr, mean 70° with 0.02 in. rain); June 10-11 (16 hr, mean 76°, with 0.19 in. rain); June 11-12 (14 hr, mean 70° with 0.11 in. rain); June 12-13 (16 hr, mean 70° with 0.44 in rain). Total rainfall for June 9-13 at our AREC was 1.36 inches but volumes with the several storms varied widely throughout the local area and there was also scattered hail in some locations.

Temperatures and length of wetting during these events favored secondary apple scab and early summer disease development. Cedar rust galls were producing spores through all of these events, but are nearly depleted now. Secondary spread of fire blight was possible where growing shoot tips are still susceptible.

In addition to developing activity by the usual summer diseases, with these recent warmer wetting periods, be alert for possible early indications of Alternaria leaf blotch on Red Delicious and Glomerella leaf spot on Gala, Golden Delicious and Cripps Pink (Pink Lady) apples. This is also a critical time for protection against Brooks fruit spot.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (CWH) from rainfall or dew, starting 10 days after petal fall. As of Friday afternoon, June 13, we had accumulated 136 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

Infection conditions for June 9-13 were similar at Tyro, VA. As of June 12, a sensor placed in an apple tree at 1165 ft. elevation had accumulated 90 wetting hours from May 11, while one placed at 941 ft elevation had accumulated 172 hr. The station at the highest elevation (1465 ft) apparently spent some time in the clouds this week and continues to register more wetting hours than the intermediate one, 125 CWH.

Spring and summer disease update

In the past five days we have had two more apple scab and cedar-apple rust infection periods at our AREC June 4-5: 23 hours wetting at 73-60°, and June 8-9 at 74-66°. Note that cedar rust galls are still actively producing spores.

In addition to developing activity by the usual summer diseases, with the recent warmer wetting periods, be alert for possible early indications of Alternaria leaf blotch on Red Delicious and Glomerella leaf spot on Gala, Golden Delicious and Cripps Pink (Pink Lady) apples. This is also a critical time for protection against Brooks fruit spot.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (CWH) from rainfall or dew, starting 10 days after petal fall. As of this morning, June 8, we had accumulated 80 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

At Tyro, VA we selected May 11 as the start date for accumulation of wetting hours by weather stations at Tyro, VA. As of June 5, a sensor placed in an apple tree at 1165 ft. elevation had accumulated 62 wetting hours from May 11, while one placed at 941 ft elevation had accumulated 128 hr. It is interesting that the station at the highest elevation (1465 ft) registered more wetting hours than the intermediate one, 81 CWH.

Scab and rust infection period; fire blight; tracking sooty blotch and flyspeck development

We recorded another apple scab and cedar-apple rust infection period at our AREC May 29-30: 22 hours wetting with 0.6 inches of rain at 55-58°.

Last week we had several reports and observations of fire blight outbreaks. The onset of symptoms and local temperature history over the past several weeks indicate that these probably dated back to secondary infection that occurred about May 13, when there were some strong storms in the area.

For purposes of predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. This year we have chosen May 8 as our petal fall start date for Winchester, so the start of wetting hour accumulation is from May 18. This is 5 days later than 2013 and 30 days later than 2012. By the end of the wetting period Friday, May 30, we had accumulated 33 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. 

A caution to those further south and east of the Blue Ridge: Your petal fall date may have been a week or more ahead of ours and we have arbitrarily selected May 11 as the start date for accumulation of wetting hours by weather stations at Tyro, VA. One of the purposes of having three weather stations at this location was to compare wetting hour accumulation at different elevations. As of May 30, a sensor placed in an apple tree at 1165 ft. elevation had accumulated 50 wetting hours from May 11, while one placed at 941 ft elevation had accumulated 109 hr!

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.

Heavy scab and rust infection period; fire blight risk moderate to low

Scab and rusts: Extended wetting began at our AREC, Winchester, at 3 PM Monday Apr 28 and will likely extend through the night to Thursday morning, May 1, a total of more than 60 hours. Temperatures for this heavy scab infection period ranged from 59 F to 46 and back up to the mid-50s. Because the beginning and ending temperatures also favored quince rust and cedar-apple rust infection at peak susceptibility of blossoms to quince rust, follow-up fungicide mixtures should be selected that include after-infection rust control. 

This extended wetting also favors peach scab infection.

Central Virginia has had similar conditions this week, with almost continuous wetting, starting at 2 PM Apr 28 and about 2.5 inches of rain recorded at Tyro.

Fire blight outlook: With cooler than predicted temperatures, the fire blight risk through this weekend remains moderate to low. But the 10-day forecast shows warmer temperatures toward the middle of next week, and with an extended bloom period, this will bring higher risk of fire blight to later bloom. The fire blight outlook will be updated May 3.

Powdery mildew: The 10-day forecast shows dry weather, favorable for mildew infection through the period. Earlier we had 13 dry weather mildew infection days since Apr 9, so secondary mildew pressure on susceptible cultivars will be heavy in the coming weeks, and tank mixes of fungicides should also include a material for mildew suppression. 

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 cropped graphic from the Maryblyt 7 program. Most apple cultivars at our AREC are near full bloom, but with delayed blossoms continuing to open over the next several days. Later cultivars such as Rome Beauty are just starting to bloom. This prediction is for trees with first bloom open Monday, April 20, 2014. The temperature and rainfall data are current through this morning,  April 28. Predicted weather conditions are shown for April 28-May 7. 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 will be high for Apr 30-May 1. If the temperatures were five degrees warmer for those two days, infection would be predicted for May 1. Following the higher risk for Apr 30-May 1, the current forecast with cooler predicted temperatures holds the risk at a low to moderate rating through May 7. 

This graphic will be updated April 30. 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 April 25-26

We recorded 12 hours of wetting at 53-62° at our AREC, Winchester April 25-26, an apple scab, quince rust and cedar-apple rust infection period. Where protection was not adequate, growers are advised to follow up with an SI fungicide to offset possible infection of blossoms, which are now very susceptible to quince rust. Extended wetting is likely tonight and during the next several days.

Fire blight and fungal disease update, April 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: The fire blight outlook has varied with a changing forecast the past several days. Above is a cropped graphic from the Maryblyt 7 program. Most apple cultivars at our AREC have bloom open, some are nearing full bloom and many flowers are expected to open over the next several days. This prediction is for trees with first bloom open April 20. The temperature and rainfall data are current through this morning,  April 25. Predicted weather conditions are shown for April 25-May 4. 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 current predicted temperatures and wetting, the risk column shows that fire blight infection will remain moderate until May 1. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Following briefly higher risk on May 1, the current forecast shows cooler predicted temperatures which hold the risk at a low or moderate rating through May 4. These cool temperatures will also prolong the bloom period and increase the possibility of fire blight infection with warmer temperatures on late bloom.

This graphic will be updated April 28. 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.

Other diseases: Extended wetting at relatively warm temperatures tonight will likely result in apple scab and rust infection, and blossoms are now very susceptible to quince rust. Rain and shower activity next week Apr 28-30 will also favor rust and scab infection. Expect scab lesions from April 11-15 infection periods to be present during Apple Blossom Festival weekend.

Powdery mildew spores were available under favorable dry weather infection conditions by Apr 9, and we have had 12 dry weather “mildew infection days” since Apr 9.

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. Most apple cultivars at our AREC have bloom open, some like Idared, are approaching full bloom and many flowers are expected to open over the next several days. This prediction is for trees with first bloom open Monday, April 20, 2014. The temperature and rainfall data are current through this morning,  April 23. Predicted weather conditions are shown for April 24-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 will be high for Apr 25, but the temperatures would need to be warmer over the next two days for infection to be predicted for Apr 25. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Following the higher risk on Apr 25, the current forecast with cooler predicted temperatures holds the risk at a low to moderate rating through May 2. 

This graphic will be updated April 25. 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 caution

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. With early cultivars with bloom open, and more bloom opening over the next several days, here is a prediction for trees with first bloom open yesterday, April 20, 2014. The temperature and rainfall data are current through this evening, April 21. Predicted weather conditions are shown for April 22-26. 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 high. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher.  Infection would be more likely in areas where bloom is more advanced, and temperatures are a couple degrees warmer than that shown for Apr 25 or 26, and if wetting occurs Apr 25-26. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. 

This graphic will be updated April 23, or sooner if 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.

Apple scab and rust infection April 14-15

Ginger Gold apple bud stage, April 16, 2014

As shown above, apples at our AREC were mostly in open cluster bud stage Wednesday morning, April 16.

Scab and rust infection period:  We had about 13 hr wetting in the 59-64° range Apr 14-15, followed by another 10 hr wet as the temperature dropped from 55 to 38. This was plenty enough for scab, quince rust and cedar-apple and infection.

As usual, we saw powdery mildew spores emerging from tight cluster stage buds last week, and mildew infection would have occurred with dry weather April 9-10 and 13-14, so we should now be spraying apples for scab, the rusts and mildew.

After-infection control of rusts: Quince rust and cedar-apple rust spores were released and likely found a susceptible target in apple blossoms at open cluster.  It is best to include an SI fungicide for after-infection control of rusts, especially quince rust, considering yesterday’s warm infection period. If an EBDC fungicide had been applied just before the rain, it may have weathered through with less than an inch of rain, but where rainfall was more an inch or the most recent fungicide application was more than a week earlier, applied more than a week ago, it is best to follow-up with a supplemental SI fungicide for after-infection control of rusts.

Fire blight?: The warm temperatures over the weekend to Apr 15 might have favored fire blight Apr 14-15 if bloom opened April 11-13, but fire blight infection was not likely where bloom first opened during the day April 14 or 15. Now it looks like it will remain relatively cool into next week, but with warmer temperatures and more bloom expected by the middle of next week. Of course the fire blight threat can change quickly if the temperatures are warmer than predicted.

TYRO, VA: Similar apple disease scenarios were expected for central Virginia, where the bud stage is more advanced with bloom open last week, temperatures generally several degrees warmer and rainfall reported to be as much as 2.4 inch.

Scab infection at Winchester Apr 11-12

At our AREC near Winchester, wetting which began at 6 PM Apr 11 and continued for 14 hours at 64-40° F was long enough for a scab infection period. Total rainfall during the infection period was only 0.01 inch.


Wetting during this event was not long enough for scab infection at Tyro, Apr 11-12.

Wetting April 7-8 Winchester and Tyro, VA

Apple buds at our AREC are now at 1/2-inch green-tip stage with some approaching tight cluster. 

With wetting starting at 6 AM yesterday, and starting to dry as of 8 AM this morning, we did not have enough wetting for a scab infection at 38-44° F.

Wetting in the Tyro area, central Virginia, began at 4 AM Apr 7 and continued for more than 26 hours at 42-47° F with 1.25 inch rain. This was more than adequate for a scab infection period. Tyro also was close to an infection period  Apr 3-4 with 11 hr wet with light rain and temperatures 51-59° F.

Expect the release of powdery mildew conidia as buds approach the tight cluster stage.

At last, it's a new season!

On Monday, March 31, we saw our first green-tip stage showing on Gala (above) and Red Delicious apples, and that raises the question whether wetting March 29-30 was enough for a scab infection period. 

At our AREC, we had just enough wetting (18 hr wet at 48-40° F, with 0.54 inch of rain), and we did trap scab ascospores, but probably had very little green tissue exposed during the wetting period.

This year, we will be tracking and reporting disease update information based on data we are receiving from weather stations placed in Silver Creek Orchards, Pharsalia Road in Tyro, Nelson County, Virginia. Green tip was also reported on Pink Lady apples in that area. There was considerably more wetting in Tyro than at Winchester, easily long enough for scab infection: 26 hr wet at 57-48° F, then 3 hr dry, followed by 7 more hours wet at 34-44°, with a total of 1.72 inch of rain. There was probably enough green tissue exposed during the wetting, so the only question is whether scab ascospores were present and mature for the wetting event. Wherever there was scab present in the orchard or on nearby untended trees in fall  2013, spores were likely mature and available to infect.

Where apples are just beginning to show green-tip, it is definitely time for protective fungicides such as copper or EBDCs; however, if green tissue was exposed during this potential infection event, it would be prudent to include a fungicide with after-infection activity with the protectant if this is the first fungicide application. We have found Vangard (cyprodinil) to be compatible with copper, and effective in such situations. Because of fruit russet concerns, copper materials should not be applied to fresh market fruit after 1/4-inch green-tip stage. 

We thank Dr. Mizuho Nita, grape pathologist with Alson H. Smith AREC, Winchester, for procuring funding and placing the weather stations in Tyro. We also thank John Saunders, Silver Creek Orchards, for hosting these weather stations and helping us to install them. As the season progresses, we hope to compare accumulated wetting, temperature, and infection conditions within adjacent grape and apple leaf canopies at three elevations from approximately 944-1462 ft. Dr. Nita's funding came from a VDACS SCRI block grant (Virginia Dept. of Agriculture and Consumer Services, Specialty Crop Research Initiative).