Monday, June 20, 2016

Increasing summer disease pressures

At Winchester last week we had two significant extended wetting events favorable for SBFS and fruit rot development: June 15-16: 11 hr at 76-72°, with 0.46 in. rain, and June 16-17: 15 hr at 69-63° with 1.95 in. rain. Much of this rain came at the beginning of the event, and this volume of rainfall would have depleted much of the protective fungicide residue, leaving the fruit exposed to potential rot infection.

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 began wetting hour accumulation at Winchester from May 14. As of Monday, June 20, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 257 hr (with the 250-hr threshold reached June 5); at 952 ft elevation, 248 hr (near the threshold); and at the 983 ft elevation, 218 hr ACW.

At Tyro, VA we started wetting hour accumulation May 4, and as of June 20, a sensor placed at the 941 ft elevation had accumulated 315 hr (with the 250-hr threshold reached June 6); the one at 1165 ft. elevation had accumulated 188 wetting hours, and the one 1465 ft. elevation had accumulated 213 wetting hours. 

At both Winchester and Tyro, most of the wetting hour accumulation at the higher elevations has been only with rain events, while accumulation at the lowest elevation has been with dew as well as rain events.

Summer disease management should be directed toward the array of potential problems in specific orchard blocks, utilizing protective fungicides for general purposes, but supplementing them with more specifically active fungicides directed at higher disease pressures and special control problems. Expect higher fruit rot pressures where fire blight killed shoots and fruit mummies are present in the trees. For more information on the effectiveness of apple fungicides for management of sooty blotch/flyspeck, Brooks fruit spot, black rot, white rot and bitter rot consult Table 6 (pp. 53-54) in the 2016 Spray Bulletin for Commercial Tree Fruit Growers.

Tuesday, June 7, 2016

Sooty blotch/flyspeck thresholds reached at Winchester and Tyro; extended wetting events


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 began wetting hour accumulation at Winchester from May 14. As of Monday, June 6, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 257 hr (with the 250-hr threshold reached June 5); at 952 ft elevation, 194 hr; and at the 983 ft elevation, 185 hr ACW.

At Tyro, VA we started wetting hour accumulation May 4, and as of June 6, a sensor placed at the 941 ft elevation had accumulated 245 hr (with the 250-hr threshold reached June 6); the one at 1165 ft. elevation had accumulated 173 wetting hours, and the one 1465 ft. elevation had accumulated 200 wetting hours.

The sensors at the higher elevations at both Winchester and Tyro could reach the threshold ACW within the next week or two, and similar accumulations should be expected for the Carroll-Patrick, Roanoke-Botetourt and Rappahannock-Madison fruit production areas.

At Winchester we had two more extended wetting events at relatively warm temperatures favorable for SBFS and fruit rot development and secondary scab infection last week: June 2-3: 19 hr at 75-64°, with 0.3 in. rain,  and June 4-5: 16 hr at 75-67°.

Wednesday, June 1, 2016

Extended wetting events May 24-31 and accumulated wetting hours

We had five extended wetting events the last week of May, and temperatures of several of these ranged into the high 60s and 70s, favorable for summer diseases as well as secondary scab infection: May 24, 9 hr wet at 57-50° with 0.04 in. of rain, May 26-27, 12 hr wet at 70-64° with 0.08 in. of rain, May 27-28, 15 hr wet at 73-63° with 0.2 in. of rain,  May 29-30, 15 hr wet at 73-61° with 0.04 in. of rain and May 30-31, 12 hr wet at 72-60° with 0.04 in. of rain.

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 again chosen May 4 as our petal fall date for Winchester, and the start of wetting hour accumulation is from May 14. As of Monday, May 30, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 172 hr; at 952 ft elevation, 128 hr; and at the 983 ft elevation, 116 hr ACW.

At Tyro, VA we started wetting hour accumulation May 4, and as of May 30, a sensor placed at 1465 ft. elevation had accumulated 153 wetting hours, the one at 1165 ft. elevation had accumulated 124 wetting hours, and the one placed at 941 ft elevation had accumulated 175 hr.

Mildew-susceptible cultivars are showing considerable secondary infection, a result of the earlier 28 dry weather mildew infection days through May. 

Tuesday, May 24, 2016

Transition to summer diseases

We have had extremely cool conditions the first three weeks of May, with temperatures reaching the 80s only one day (May 2) and barely nudging the 70s only five other days. We are now seeing the development of scab and cedar-apple rust lesions from the infection periods outlined in previous posts: Apr 22-23 and Apr 28-May 12. Mildew-susceptible cultivars are showing considerable secondary infection, a result of the earlier 24 dry weather mildew infection days through Apr 25. Two more extended wetting events last week favored secondary scab and moldy core infection and kicked off the early summer disease pressures. These were: May 21, 14 hr wet at 54° with 0.62 in. of rain, and May 21-23, 33 hr wet at 54° with 0.34 in. of rain. (Actually these two could be lumped together, increasing the threat of fruit infection where primary scab was not well-controlled Apr 22-May 5).

Fire blight infection symptoms appeared locally as early as May 9, from infection that occurred Apr 21-26; symptoms from infection May 2-3 are expected later this week. After we reach late bloom in most years, temperatures are warm enough that protection of late bloom is routinely needed. However this year we have gone 19 consecutive days without infection conditions. But this week conditions return to "normal", with temperatures in the 80s increasing the risk (EIP, effective inoculum potential) to an infective level wherever wetting occurs on late bloom remaining into next week. Continue to protect prolonged bloom, especially on newly planted trees, as needed. With the prolonged cool conditions, we are still seeing late bloom on varieties such as Rome three weeks after we would like to be finished thinking about fire blight!

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 again chosen May 4 as our petal fall date for Winchester, so the start of wetting hour accumulation is from May 14. As of Monday, May 23, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 94 hr; at 952 ft elevation, 76 hr; and at the 983 ft elevation, 73 hr ACW.
To those farther south and east of the Blue Ridge, your normal petal fall date would have been a week or more ahead of ours at Winchester, so we have selected Apr 27 as the petal fall 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, but because many of the early wetting hours were a result of rainfall rather then dew, the early accumulation trend this year is a bit different than in previous years. As of May 23, a sensor placed at 1465 ft. elevation had accumulated 130 wetting hours from May 4, the one at 1165 ft. elevation had accumulated 107 wetting hours, and the one placed at 941 ft elevation had accumulated 133 hr.

Saturday, May 14, 2016

Disease conditions May 8-12

Wet weather disease conditions persisted this week with infection periods each day May 8-12: May 8: 8 hours wet at 52-56° with 0.1 in. of rain; May 9: 15 hr wet with 0.1 in. of rain; May 10: 8 hr at 53° with 0.03 in. of rain; May 10-11: 19 hr at 55° with 0.25 in. of rain; May 11-12: 16 hr at 55° with 0.16 in. of rain. This now totals 13 infection periods in 15 days! Several of these infection periods again involved both scab and rusts.

Hopefully, the fruits of most varieties are now big enough that they have become resistant to quince rust . However, Romes and some other varieties with late bloom where there was frost damage might be the exception. There still is some cedar-apple rust inoculum left that could infect the youngest leaves, but the long wetting periods are now depleting much of the rust inoculum. This week we saw cedar-apple rust lesions developing from infection that occurred Apr 22-23. (Photo by Allen Cochran II below).
Early cedar-apple rust symptoms on York apple leaf. May 10, 2016. 
With this amount of wetting during the bloom and immediate post-bloom growth stages, moldy core becomes an unusual concern on varieties such as Red Delicious, Fuji, and Cameo. Moldy core is caused by as many as 14 different fungi that invade during the six-week period that the calyx tube stays open, so broad-spectrum residual fungicide protection is the most effective approach to avoiding this problem. Although the recent volume of rain has not been extreme given the number of wetting periods and hours of wetting that we’ve had, but the conditions have made it difficult to maintain adequate protection the past two weeks.

Fire blight: This week we saw fire blight blossom infection symptoms (shown below) on unprotected York apple trees, resulting from infection that occurred about Apr 20-21. Continue to protect prolonged late bloom as needed. 
Advanced blossom blight symptoms May 10, 2016

Sunday, May 8, 2016

Heavy apple scab pressure April 28 -May 7

Last week, following four scab/rust infection periods during April 28 to May 2, we had four more infection periods: May 2-3: 15 hours wet at 65-58° with 0.1 in. of rain; May 3-4: 16 hr wet at 66-46° with 0.08 in. of rain; May 4-5: 20 hr at 57-48° with 0.4 in. of rain; May 5-7: 38 hr at 54-48° with 0.97 in. of rain. This totals eight infection periods in ten days! Several of these infection periods involved both scab and rusts.
Remaining apple blossoms and small fruit may still be susceptible to quince rust so it is prudent to include a sterol-inhibiting fungicide for after-infection rust control in the next fungicide application. Scab and rust lesions from the Apr 22-23 infection period are expected to start appearing this week.
Fire blight: Continue to protect prolonged bloom as needed. 
Powdery mildew: We have had 21 dry weather “mildew infection days” since mildew spores were first available Mar 16.

Monday, May 2, 2016

Recent scab and rust infection periods and fire blight outlook, May 2, 2016

At our AREC in Winchester, we have had four scab or rust infection periods within the past four days. April 28-29: a heavy apple scab and rust infection period: 31 hours at 53-46° with 0.67 in. of rain; Apr 30: 10 hours at 51° with 0.01 in. of rain; Apr 30-May 1: 18 hours at 53° with 0.53 in. of rain; May 1-2: 12 hours at 59° with 0.16 in. of rain. Locally, some of these wetting periods may have been extended by showers or foggy conditions. Apple blossoms and small fruit are still very susceptible to quince rust so it would be prudent to include a sterol-inhibiting fungicide for after-infection rust control in the next fungicide application.

FIRE BLIGHT: Below is a cropped graphic from the Maryblyt 7 program. Susceptible blossoms are still present on some cultivars. The temperature and rainfall data are current through Monday morning, May 2. Predicted weather conditions are shown for May 2-7. 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, the risk column shows infection conditions for Apr 21, 22 and 24-26. The fire blight risk remains high for May 2-4, and slightly warmer temperatures with wetting could result in infection. For optimum control, a protective streptomycin application is recommended ahead of predicted infection, but it can also provide about one day after infection suppression.


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. Be aware that risks on late bloom can change quickly with unpredicted warmer temperatures and wetting. 

Friday, April 29, 2016

Heavy scab and possible rust infection period; fire blight outlook

As of 8 AM April 29 we had recorded a heavy apple scab and possible rust infection period: 30 hours at 53-46° with 0.44 in. of rain. The cedar galls and quince rust cankers are now in "full bloom", producing basidiospore inoculum, and the apple blossoms and small fruit are very susceptible to quince rust. The first 12 hours of wetting at 53° would have have been more favorable for infection by the rusts than the later 18 hours with temperatures down to 46°. With continued sporadic wetting in the 50s likely, it would be prudent to include a sterol-inhibiting fungicide for after-infection rust control in the next fungicide application.

Maryblyt outlook for Winchester, VA, April 29.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Susceptible flowers are still open on many cultivars. The temperature and rainfall data are current through Friday morning, April 29. Predicted weather conditions are shown for April 29-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, the risk column shows infection conditions for Apr 21, 22 and 24-26.
 Cooler temperatures Apr 29-30 should reduce risks through Apr 30, but predicted warmer temperatures Sunday, May 1 will again increase the risk going into next week. For optimum control, a protective streptomycin application is recommended ahead of predicted infection, but it can also provide about one day after infection suppression. Risk can change quickly with unpredicted warmer temperatures and wetting.

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. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. The fire blight outlook will be updated Monday, May 2.

Wednesday, April 27, 2016

Fire blight infection conditions today

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. Susceptible flowers are still open on most cultivars. Here is the prediction for trees with first bloom open Monday, April 11, 2016. The temperature and rainfall data are current through Wednesday morning, April 27. Predicted weather conditions are shown for April 27-May 1. 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, which has been true since Apr 18. Based on predicted temperatures, the risk column shows infection conditions for Apr 21-22 and 24-27. (Note that the outlook for Apr 25-26 changed from the previous post due to unpredicted showers both days). For optimum control, a protective streptomycin application is recommended ahead of predicted infection, but it can also provide about one day after-infection suppression. Predicted cooler conditions after today and through APPLE BLOSSOM FESTIVAL weekend should reduce risks during this time. (The cooler temperatures will probably also ensure that a few apple blossoms will be present through the weekend for those who come to the area looking for them).

The BBS column is tracking predicted symptom development for the first infection Apr 21. Yesterday we could already see symptoms from experimental inoculations Apr 18. The CBS column predicted for the appearance of canker margin symptoms Apr 26, due to extension of overwintering cankers from last year, and it is now tracking the predicted appearance of canker blight symptoms when that value reaches 100. Canker blight cannot be prevented by chemical treatment and the presence of symptoms would signal 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 WeatherChannel for Winchester, supplemented by site-specific data from SkyBit Inc. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. Unless the outlook changes appreciably form currently predicted conditions, the fire blight outlook will not be updated until Monday, May 2.

Monday, April 25, 2016

Fire blight and other disease threats this week

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 outlook April 25, 2016
FIRE BLIGHT:  Above is a cropped graphic from the Maryblyt 7 program. Susceptible flowers are still open on most cultivars. Here is the prediction for trees with first bloom open Monday, April 11, 2016. The temperature and rainfall data are current through Monday morning, April 25. Predicted weather conditions are shown for April 25-29. 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, which has been true since Apr 18. Based on predicted temperatures, the risk column shows infection conditions for Apr 21, 22 and 23 and only wetting is lacking for Apr 25-27. In situations where all other requirements for infection have been met except wetting, wetting from a maintenance spray application can provide the wetting trigger for infection to occur. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. A streptomycin spray remains effective about 3 days in warmer conditions when it is needed most and can provide about one day after-infection suppression.

The BBS column is tracking predicted symptom development for the first infection Apr 21. The CBS column indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which are predicted to occur when that value reaches 100 Apr 27. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will signal 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. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. The fire blight outlook will be updated Wednesday, Apr 27.

OTHER DISEASES:  We recorded a 15-hr scab, cedar-apple rust and quince rust infection period Apr 22-23. The infection period was as long as 23 hr in Tyro, VA. Where fungicides were not applied recently enough to cover through this infection event, we suggest ones with after-infection activity for scab and rusts, applied as soon as possible. 
Cedar-apple rust galls with expanded spore horns April 22, 2016.
Meanwhile, powdery mildew has been by far our most active apple disease so far this year. Mildew is our only "dry weather" disease and we have had 24 infection days since spores were first available March 16. Secondary infection, shown below, has been evident for at least two weeks. 
Secondary powdery mildew infection, Ginger Gold apple.
Peach leaf curl infection occurred at our AREC as early as March 13. Complete control can be achieved with a single application of an effective fungicide in the dormant season any time from leaf drop in the fall until just before infection occurs with wetting after first bud swell in the spring.
Peach leaf curl, Turk Mt. Overlook, Skyline Drive, Virginia

Finally, after the early season we have had this year, we are happy to see peach and apple trees making little fruits at our AREC!
Shuck-split stage on Redhaven peach, April 22, 2016, 

Friday, April 22, 2016

Current fire blight conditions

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. Susceptible bloom is open on all cultivars. Here is the prediction for trees where first bloom was open Monday, April 11, 2016. The temperature and rainfall data are current through Friday morning, April 22. 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). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher, which has been true since Apr 18.

Based on predicted temperatures, the risk column shows infection conditions for Apr 21-24 and Apr 26 and only wetting is lacking for Apr 25. In situations where all other requirements for infection have been met except wetting, wetting from a maintenance spray application can provide the wetting trigger for infection to occur. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. A streptomycin spray remains effective about 3 days in warmer conditions when it is needed most and can provide about one day after-infection suppression.

The BBS column is tracking predicted symptom development for the first infection Apr 21. The CBS column indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which are predicted to occur when that value reaches 100 Apr 26. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will signal 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. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Monday, Apr 25.

Wednesday, April 20, 2016

Continued fire blight risk into next week

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. Susceptible bloom is open on all cultivars. Here is the prediction for trees with first bloom open Monday, April 11, 2016. The temperature and rainfall data are current through Wednesday afternoon, April 20. Predicted weather conditions are shown for April 21-25. 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). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher, which is occurring today, Apr 18. Based on predicted temperatures, the risk column shows high risk for Apr 18-23 and Apr 25. Infection is indicated with predicted thunderstorms Apr 23. Be aware that in situations where all other requirements for infection have been met except wetting (Apr 18-22 and 25), wetting from a maintenance spray application can provide the wetting trigger for infection to occur. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

The CBS column at the right in the graphic indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which would be predicted to occur when that value reaches 100. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will signal 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 WeatherChannel for Winchester, supplemented by site-specific data from SkyBit Inc. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Friday, Apr 24.

Monday, April 18, 2016

Fire blight active this week!

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. Susceptible bloom is open on all but late cultivars (Even Rome Beauty clusters are waking up!), and earlier cultivars are approaching full bloom. Here is the prediction for trees with first bloom open Monday, April 11, 2016. The temperature and rainfall data are current through Monday morning, April 18. Predicted weather conditions are shown for April 18-23. 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, which is occurring today, Apr 18. Based on predicted temperatures, the risk column shows high risk for Apr 18-22, with only wetting lacking as the trigger for fire blight infection these days. Infection is indicated with predicted showers for Apr 22. Be aware that in situations where all other requirements for infection have been met except wetting (Apr 18-22), wetting from a maintenance spray application can provide the wetting trigger for infection to occur. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

The CBS column at the right in the graphic indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which would be predicted to occur when that value reaches 100. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will signal 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 WeatherChannel for Winchester, supplemented by site-specific data from SkyBit Inc. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Wednesday, Apr 20.

Friday, April 15, 2016

Fire blight outlook for the Winchester area, April 16-22

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. Susceptible bloom is open on most cultivars. Here is the prediction for trees with first bloom open Monday, April 11, 2016. The temperature and rainfall data are current through Friday afternoon, April 15. Predicted weather conditions are shown for April 16-22. 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). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher, which is predicted to occur Apr 18. Based on predicted temperatures, the risk column shows high risk for Apr 18 and Apr 20-22, and only wetting is lacking as a trigger for fire blight infection those days. Be aware that in such situations, the wetting by a maintenance spray application can meet the wetting requirement for infection to occur when the EIP is above 100 and all other requirements for infection have been met. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

The CBS column at the right in the graphic indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which would be predicted to occur when that value reaches 100. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will signal 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 WeatherChannel for Winchester, supplemented by site-specific data from SkyBit Inc. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Monday, Apr 18.

Wednesday, April 13, 2016

Fire blight outlook for the Winchester area, April 13-18

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 bloom is now open on many apple cultivars. Here is the prediction for trees with first bloom open Monday, April 11, 2016. The temperature and rainfall data are current through Wednesday morning, April 13. Predicted weather conditions are shown for April 13-20. 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 record temperatures and wetting, the risk column shows high risk for Apr 11, but the EIP had not yet reached 100 and would have required max/min temperatures 9 degrees warmer to reach the infective level. There were occasional blossoms open at our AREC as early as Apr 8, but with the indicated temperatures, that would have made little difference in the risk interpretation for Apr 11. With cooler predicted temperatures through the rest of this week, fire blight risk should remain low to moderate. However, with warmer predicted temperatures Apr 17-18, the EIP would again approach the infective level by Apr 18.


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. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. This fire blight outlook will be updated Friday, April 15.

FUNGAL DISEASES: Powdery mildew remains our most active early season apple disease, with 13 dry weather mildew infection days recorded since March 16. Primary and secondary mildew infection will likely become more evident after we get some consistently warmer growth conditions.

Wednesday, March 30, 2016

Gradual bud movement to pre-pink



We have seen gradual bud movement at Winchester since the previous post on March 18. Above are the same Red Delicious buds that were pictured previously at green-tip stage. They now are showing some color in the pre-pink stage. Most cultivars at our AREC were at tight cluster stage, but will advance more rapidly in the next couple days.

It looks like we are headed for the first 2016 apple scab and cedar-apple and possibly quince rust infection period at our AREC Thursday night and Friday morning Mar 31-Apr 1. Hopefully there has been ample opportunity to protect the developing buds as they moved through the tight cluster stage. Cedar-apple rust galls are plentiful in some areas, even to the point of causing browning of the foliage as shown below.


Cedar-apple rust galls on eastern red cedar near Winchester, VA

I noted that we had seen apple powdery mildew conidiospores by March 17, and in the interim we have already recorded 8 mildew infection days. So you might say that, in this Spring Training exercise, the mildew has outscored scab 8-0!


Redhaven peach trees (shown below) are now approaching full bloom.




In-depth meeting March 31:
Finally, this is a reminder that our first In-Depth Meeting of the new season will be held at Alson H. Smith Jr. AREC, 595 Laurel Grove Road, Winchester, VA, starting at 7 PM Thursday, March 31. Following an entomology update by Dr. Chris Bergh, we will address early season disease management issues and end with some recent pathology questions and answers.

Friday, March 18, 2016

It's a new season!




At our AREC we had green tip on Red Delicious (shown above) and other apples March 16 and about 1/4-inch green by March 17. 55 hours of wetting, with discharge of apple scab ascospores, had occurred from March 13-15. This was more than three times the length of wetting required for scab infection where green tissue was exposed, but our buds had not advanced to that stage by that time. 

Scab infection was likely in areas where buds were more advanced to the green-tip stage. In Tyro, Virginia, 51 hours of wetting was recorded at temperatures that were about 5 degrees warmer than at Winchester, resulting in more than four times the length of wetting required for scab infection. Apple scab ascospore maturity at green-tip stage is normal and should be expected except in years when buds advance rapidly without any moisture to mature the spores. 

Powdery mildew spore production is advanced compared to most years. Typically, buds infected with overwintering mildew are somewhat delayed compared to their healthy counterparts. However, I was surprised to see mildew-infected buds as advanced as healthy ones (upper right, below), and they had an abundance of conidia (below). In contrast to wetting conditions needed for scab infection, powdery mildew is able to infect on dry days with temperatures above 53 degrees F.

Mildew infected Idared bud, upper right.

Mildew conidia on Idared. Winchester, March 17, 2016
Cedar-apple rust galls are also ready to produce infective basidiospores with the next warm wetting period, so protective apple fungicides should now be included for mildew and rusts as well as for scab. 
Cedar-apple rust gall ready to produce spores March 16. Virginia Tech AREC, Winchester.
Redhaven peach bud development at Virginia Tech AREC, Winchester, March 17, 2016.
Peach buds (above) were more advanced than apples, and unprotected buds would have been readily susceptible to leaf curl infection with wetting March 13-15. Because spores of the leaf curl fungus are carried on the surface of the tree from the fall to spring, fungicides applied in the fall or during the winter give good protection from leaf curl. Fall applications help to avoid the spring rush to spray before pruning brush is removed from the orchard.

Friday, September 4, 2015

Bitter rot and summer disease pressures

This week we have had several reports of bitter rot showing up in Frederick County. For several weeks we have also seen it in our research plots at the AREC. Some may be associated with fire blight strikes, but more frequently they seem to be related to the presence of small fruit or flower mummies that served as the likely inoculum source.
Bitter rot on an Idared fruit with a small mummy, a probable inoculum source
Although it was quite dry throughout most of August, the bitter rot infection relates to warm wetting conditions as early as mid-May. From May 16 to Aug 11 we had 21 extended wetting periods at temperatures in the 70s and higher 60s, favorable to bitter rot activity. At our AREC we had only 0.14 in.of rain from Aug 11 to Sept 2, but some county locations have recorded considerably more rainfall than we have had at the AREC in the past month, so that adds to the potential problems. Although these conditions could also favor Glomerella leaf spot development, so far we have not had reports of this from Frederick County.

While we lacked wetting from rainfall, we continue to add accumulated wetting hours from dew. As of the Monday morning, Aug 31, total accumulated wetting hours (ACW) at the AREC were: at 909 ft elevation, 975 hr; at 952 ft elevation, 673 hr; and at the 983 ft elevation, 576 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 5.5 wetting hours per foot of elevation drop from 983 to 909 ft. Continue to scout for sooty blotch, flyspeck, and fruit rots, especially at lower elevations in an orchard.

At Tyro, in Nelson County, total ACW as of Monday morning, Aug 31, were: at 941 ft elevation, 792 ACW; at 1165 ft, 415 ACW; and at 1465 ft, 473 ACW. An extended wetting event with substantial rainfall was recorded at Tyro Aug 18-19, 25 hr wet at 74-69° at the highest elevation.

Thursday, August 20, 2015

Summer disease update

Summer disease pressures remained steady last week.  The extended wetting event Aug 10-11, in progress at the time of the last post, amounted to 12 hr wet at 71° with 0.31 in. of rain.

As of the Monday morning, Aug 17, total accumulated wetting hours (ACW) at the AREC were: at 909 ft elevation, 864 hr; at 952 ft elevation, 611 hr; and at the 983 ft elevation, 539 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 4.4 wetting hours per foot of elevation drop from 983 to 909 ft. The wetting hour accumulation differential is greater during times when wetting is from dew rather than during wetting from rain, because rain tends to wet both locations similarly. In the past 10 days we have recorded only 0.17 inch of rainfall, but recorded 87 hours of wetting from dew at the 909 ft elevation.  This is why we say to scout for sooty blotch, flyspeck, and fruit rots at lower elevations in an orchard.

At Tyro, in Nelson County, total ACW as of Monday morning, Aug 17, were: at 941 ft elevation, 718 ACW; at 1165 ft, 385 ACW; and at 1465 ft, 433 ACW. An extended wetting event with substantial rainfall was recorded at Tyro Aug 18-19, 16 hr wet and 1.2 in. of rain at 74-69°.

Tuesday, August 11, 2015

Increasing summer disease and brown rot pressures

Summer disease pressure increased in the past week, with two extended wetting events at our ARECAug 6-7, 16 hr wet at 68-65° with 0.11 in. of rain and Aug 9-10, 16 hr wet at 74-72° with 0.52 in. of rain. (Another extended wetting event is in progress at the time of this post).

As of the Monday morning, Aug 10, total accumulated wetting hours (ACW) at the AREC were: at 909 ft elevation, 796 hr; at 952 ft elevation, 567 hr; and at the 983 ft elevation, 518 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 3.8 wetting hours per foot of elevation drop from 983 to 909 ft.

At Tyro, in Nelson County, total ACW as of Monday morning, Aug 10, were: at 941 ft elevation, 670 ACW; at 1165 ft, 368 ACW; and at 1465 ft, 409 ACW. 

The recent wetting events will again increase brown rot pressure on ripening peaches, as well as sooty blotch, flyspeck and rots on early ripening apples.

Wednesday, August 5, 2015

Summer disease update

Summer disease pressure was moderate in the past week, with one extended wetting event at our ARECJuly 28-29, 13 hr wet at 72-66° with 0.59 in. of rain. A thunderstorm during the early morning hours Aug 4 resulted in only 0.15 inch of rainfall and 4 hr wetting at our AREC, but the rainfall was likely much heavier in some Frederick County orchards.

As of the Monday morning, Aug 3, total accumulated wetting hours (ACW) at the AREC were: at 909 ft elevation, 739 hr; at 952 ft elevation, 522 hr; and at the 983 ft elevation, 476 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 3.6 wetting hours per foot of elevation drop from 983 to 909 ft.

At Tyro, in Nelson County, total ACW as of Monday morning, Aug 3, were: at 941 ft elevation, 643 ACW; at 1165 ft, 352 ACW; and at 1465 ft, 393 ACW. 

Wednesday, July 29, 2015

Dry weather great for sweet ripening peaches

At our AREC we have recorded only 0.2 inch of rain and no extended wetting periods with rain in the past two weeks. Although it is starting to get pretty dry, this has been a welcome break for ripening peaches, producing sweeter fruit with less brown rot pressure.


Ripening Redhaven peach: Dry and bright sunny weather reduces brown rot pressure in the pre-harvest period
But the blemishes from scab lesions are an indicator of earlier season disease pressures. The incubation period for scab infection to appear can be as long as 6-7 weeks, sometimes leading to the question "Where did this come from?"

Earlier rot activity is showing up as bitter rot and other rots on Honeycrisp apples, and this brings reminders that anything that causes injury such as Japanese beetle, will increase the possibility of rot activity, especially as sugar levels increase.

As of the Monday morning, July 27, accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 687 hr; at 952 ft elevation, 486  hr; and at the 983 ft elevation 444 hr ACW. 

At Tyro, in Nelson County, total ACW as of Monday morning, July 27, were: at 941 ft elevation, 595 ACW; at 1165 ft, 311 ACW; and at 1465 ft, 354 (with the 250-hr threshold reached July 5).