Wednesday, June 13, 2018

Extended wetting events; sooty blotch/flyspeck threshold reached, early bitter rot activity

In the past week at  our AREC in Winchester we recorded two extended wetting events: June 10-11, with 15 hr of wetting at 59° with 0.51 in. rain; June 11-12, with 15 hr of wetting at 59° with 0.01 in. rain. These wetting events favored early summer disease activity on apples, peach scab, cherry leaf spot and brown rot on ripening cherries. 

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 7 as our petal fall date for Winchester, so the start of wetting hour accumulation is from May 17. As of 6 PM June 13, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 276 hr; at 932 ft (the AREC NEWA station), 252 hr; and at the 983 ft elevation, 263 hr ACW. This year the wetting hours have been more a result of rainfall rather than wetting from dew, so wetting hour accumulation at different elevations is quite similar, and all have reached the 250-hr threshold. 

For central Virginia, we selected Apr 24 as the petal fall date for accumulation of wetting hours by weather stations at Tyro. As of June 13, a sensor placed at 1465 ft. elevation had accumulated only 172 wetting hours from May 4, while the one at 1165 ft. had accumulated 228 wetting hours, and the one placed at 941 ft elevation had accumulated 390 hr, and passed the 250-hr threshold for specific treatment for sooty blotch and flyspeck on May 29. Also east of the Blue Ridge, the NEWA station at Batesville has passed the 250-hr threshold with 328 ACW while the NEWA station at Gadino Cellars near Washington, VA has recorded 261 ACW using May 1 as the petal fall date. 

Two weeks ago various "rot spots" were reported on several apple varieties from central Virginia. Those have now been confirmed as incubating into bitter rot

Monday, June 4, 2018

Another wet week in Winchester

Wet weather continued this past week at Winchester and other parts of Virginia. At our AREC in Winchester we recorded three more extended wetting events: May 31-June 1, with 15 hr of wetting at an average of 70° with 0.65 in. rain; June 1-2, with 11 hr of wetting at 68° with 1.47 in. rain; June 2-3, with 28 hr of wetting at an average of 65° with 1.95 in. rain. Again these heavy rains and extended wetting at relatively warm temperatures favored secondary apple scab, early summer disease activity on apples, peach scab, cherry leaf spot and brown rot on ripening cherries. 

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 7 as our petal fall date for Winchester, so the start of wetting hour accumulation is from May 17. As of 6 PM June 3, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 207 hr; at 932 ft (the AREC NEWA station), 196 hr; and at the 983 ft elevation, 209 hr ACW. One of the purposes of following three weather stations is to compare wetting hour accumulation at different elevations. This year the wetting hours have been more a result of rainfall rather than dew, so wetting hour accumulation at different elevations is quite similar compared to previous years. 
The sooty blotch/flyspeck model on NEWA is now functioning and indicates accumulated wetting similar to the ACW shown at our NEWA station. To use this model, go to the drop-down menu for diseases and select the petal fall date to calculate the risk for that location.
Sooty blotch/flyspeck risk summary for Winchester AREC, using May 7 as petal fall date.

For central Virginia, we selected Apr 24 as the petal fall date for accumulation of wetting hours by weather stations at Tyro. As of June 3, a sensor placed at 1465 ft. elevation had accumulated only 127 wetting hours from May 4, while the one at 1165 ft. had accumulated 129 wetting hours, and the one placed at 941 ft elevation had accumulated 319 hr, and passed the 250-hr threshold for specific treatment for sooty blotch and flyspeck on May 29. Also east of the Blue Ridge, the NEWA station at Batesville has passed the 250-hr threshold with 255 ACW while the NEWA station at Gadino Cellars near Washington, VA has recorded 220 ACW with May 1 as the petal fall date. 

Monday, May 28, 2018

Early accumulation of wetting hours approaching the sooty blotch/flyspeck threshold

At our AREC in Winchester we recorded three recent secondary apple scab infection periods:  May 22, with 11 hr of wetting at an average of 67° with 0.24 in. rain; May 22-23, with 7 hr of wetting at an average of 71° with 0.02 in. rain; May 27-28, with 16 hr of wetting at an average of 69° with 0.14 in. rain. Some of the wetting occurred at temperatures near 70° and was favorable for moldy core infection and the start of summer disease activity. 

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 7 as our petal fall date for Winchester, so the start of wetting hour accumulation is from May 17. As of 6 PM May 28, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 130 hr; at 932 ft (the AREC NEWA station), 118 hr; and at the 983 ft elevation, 126 hr ACW. One of the purposes of following three weather stations is to compare wetting hour accumulation at different elevations. Typically there is a greater difference between these three locations, but this year many of the early wetting hours this year were a result of rainfall rather than dew, so wetting hour accumulation at different locations is more similar than in some previous years. 

For central Virginia, we have selected Apr 24 as the petal fall date for accumulation of wetting hours by weather stations at Tyro. As of May 28, a sensor placed at 1465 ft. elevation had accumulated only 63 wetting hours from May 4, while the one at 1165 ft. had accumulated 129 wetting hours, and the one placed at 941 ft elevation had accumulated 239 hr, approaching the 250-hr threshold for specific treatment for sooty blotch and flyspeck. Also east of the Blue Ridge, the NEWA station at Red Hill has already passed the 250-hr threshold with 307 ACW. The NEWA station at Gadino Cellars near Washington, VA has recorded 153 ACW since May 10. 

Sunday, May 20, 2018

Summary of last week's infection events, May 15-19.

At our AREC in Winchester we recorded a very long apple scab and rust infection period May 15-19, with 89 hr of almost continuous wetting at an average of 63° with 5.2 in. rain. We had observed scab lesions prior to this infection event, so potentially this was a very serious secondary infection where there was little fungicide protection to cover the event through five inches of rainfall. Some of the wetting occurred at temperatures near 70° and was favorable for moldy core infection and the start of summer disease activity. 

As a follow-up to this extreme infection period, a suggestion is to apply combinations fungicides with protectant activity and two classes of fungicides to offset the potential for resistance in apple scab; also include an SI fungicide for after-infection activity for cedar-apple rust. A second follow-up application should include another class of activity for scab plus a protectant fungicide.

This weather was also favorable for cherry leaf spot and peach scab, which will remain active for the next month. At our AREC we have had 22 apple powdery mildew infection days since Apr 10. With the long wetting last week, mildew activity was somewhat reduced, but it will be quite active with susceptible shoot growth this week

Other areas in Virginia also experienced long continuous or split wetting periods with amounts of rainfall ranging from two - five inches. We are near the transition from early season to summer disease control, but all areas should be concerned about remaining apple scab, as well as moldy core and early summer disease activity, especially bitter rot. The timing of this event might have also left an opening in protection against for Brooks fruit spot.

Wednesday, May 16, 2018

Disease update: recent and ongoing scab and rust activity

We have had a lot of apple scab and rust activity this past week, and more on the way. At our AREC we recorded scab and rust infection periods May 10-11 (15 hr wet at 62° with 0.05 in. rain), and May 14-15 (13 hr wet at 66° with 1.11 in. rain). As of the morning of May 16 another infection period is in progress and much rain and wetting is in the forecast for the next three days. We observed scab lesions, probably from infection periods Apr 15-16 or Apr 24-25, on leaves at the base of unprotected shoots. Cedar-apple rust galls are still actively producing spores. 

This weather is also favorable for cherry leaf spot and peach scab, which will remains active for the next month or so.

As indicated in the update May 14, these wetting events at temperatures in the 60s constitute fire blight infection events wherever susceptible flowers are present. Another threat is possible secondary shoot blight with bacteria spreading from blossom blight symptoms now appearing from infections May 5 and 7, and driven by a series of thunderstorms with some scattered hail.

At our AREC we have had 21 apple powdery mildew infection days since Apr 10.

Sunday, May 13, 2018

Fire blight update, May 14, 2018

FIRE BLIGHT CAUTION: We are in late bloom on Winchester area apples, and this update applies to wherever there is susceptible bloom. New plantings, late-blooming cultivars, and young trees are especially vulnerable. Below are the fire blight risk assessments, comparing graphics from Maryblyt and also from the Cougarblight model as shown on our NEWA site, using the same weather data from our NEWA station to make these comparisons. 
Graphic from Maryblyt 7, May 13, 2018. Click to enlarge.
Above is a cropped graphic from the Maryblyt 7 program, with first bloom open Apr 14. The temperature and rainfall data are current through Sunday evening, May 13. Predicted weather conditions are shown for May 14-18. 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, dew or a spray application), 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded  and predicted temperatures and wetting, the risk column shows that infection conditions occurred May 5, 7, 10, and 13, and are predicted for May 14-17 (or 18 with wetting). Thunderstorms are predicted for most days this week. High risks were shown for all of the other days between May 2 and May 11, except May 8, with only wetting lacking for infection May 2-4, 6, 9, 11, and 12. Because any spray application can serve as the wetting trigger, include streptomycin with spray applications through late bloom. Remember to protect young and recently planted trees, with flowers but considered to be "non-bearing".

The BBS column in the above graphic is tracking predicted blossom blight symptom development for the first infection May 5 (letter a), with 103% of the degree hours required for blossom symptom prediction by May 14. Letters b and c are tracking infections May 7 and 10 respectively, and predict appearance of symptoms from those on May 15 and 17. The CBS column indicates progression toward the appearance of canker margin/canker blight symptoms due to extension of overwintering cankers from last year, which was predicted for May 8. Canker blight symptoms are predicted for May 15. 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/shoot blight situation due to hail injury, etc. To offset the potential for shoot tip infection in an active fire blight year such as this one, apply the plant growth regulator, prohexadione-calcium (Apogee, Kudos), at petal fall on king bloom. Shoot blight suppression will  begin about 10 days after the initial application.

Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is extreme for May 12-19, and EIP infection conditions are shown for May 12-18.
Graphic from Cougarblight, May 13, 2018. Click to enlarge.
Similar fire blight threats remain throughout much of the region, wherever late bloom persists and wetting occurs.

Thursday, May 10, 2018

Fire blight update May 11.

FIRE BLIGHT CAUTION: We are past the peak of apple bloom in the Winchester area, but susceptible bloom remains on many varieties, including some of the earlier blooming ones such as Idared. New plantings and young trees are especially vulnerable. Below are the fire blight risk assessments, comparing graphics from Maryblyt and also from the Cougarblight model as shown on our NEWA site, using the same weather data from our NEWA station to make these comparisons. 
Graphic from Maryblyt 7, May 10, 2018. Click to enlarge.
Above is a cropped graphic from the Maryblyt 7 program, with first bloom open Apr 14. The temperature and rainfall data are current through Thursday evening, May 10. Predicted weather conditions are shown for May 11-14. 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, dew or a spray application), 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded  and predicted temperatures and wetting, the risk column shows that infection conditions occurred May 5, 7 and 10, and are predicted for May 12-14 (and later, not shown). High risks are shown for all of the other days between May 2 and May 11, except May 8, with only wetting lacking for infection May 2-4, 6, 9 and 11. Because a spray application can serve as the wetting trigger, include streptomycin with spray applications through late bloom. Remember to protect young and recently planted trees, with flowers but considered to be "non-bearing".

The BBS column in the above graphic is tracking predicted symptom development for the first infection May 5, with 101% of the degree hours required for blossom symptom prediction by May 14. The CBS column indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which was predicted for May 8. 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/shoot blight situation due to hail injury, etc. To offset the potential for shoot tip infection in an active fire blight year such as this one, apply the plant growth regulator, prohexadione-calcium (Apogee, Kudos), at petal fall on king bloom. Shoot blight suppression results from hardening off of vegetative shoot growth starting about 10 days after the initial application.

Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is extreme for May 10-16, and EIP infection conditions are shown for May 9-14.
Graphic from Cougarblight, May 10, 2018. Click to enlarge.
Similar fire blight threats remain across much of Virginia, wherever late bloom persists.

Tuesday, May 8, 2018

Disease update: apple scab, rusts and fire blight

In Winchester, we recorded a heavy apple scab and rust infection period May 5-7 with split wetting totaling 37 hr at 51-60° (mean 53°), with 0.95 in. rain. Also, many cedar-apple rust and quince rust spores were released during this extended wetting period, and flowers remain susceptibility for quince rust infection. In areas where there is a concern for rust infection, include an SI (DMI) fungicide for after-infection control in the next spray application. Rust galls remain active for more spore discharge with additional wetting. Cedar-apple rust lesions have been observed from the infection period Apr 24-25, and scab lesions should be expected this week raising the possibility of secondary infection where scab was not well-controlled at that time. Powdery mildew conidia have been available for infection at our AREC since Apr 10. Any “dry weather “ day above 53° is suitable for mildew infection and we have had 18 mildew infection days.

FIRE BLIGHT CAUTION: While we are past the peak of apple bloom in the Winchester area, susceptible bloom remains on many varieties. Below are the fire blight risk assessments, comparing graphics from Maryblyt and also from the Cougarblight model as shown on our NEWA site, using the same weather data from our NEWA station to make these comparisons. 
Graphic from Maryblyt 7, May 8, 2018. Click to enlarge.
Above is a cropped graphic from the Maryblyt 7 program, with first bloom open Apr 14. The temperature and rainfall data are current through Monday evening, May 7. Predicted weather conditions are shown for May 8-12. 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, dew or a spray application), 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded temperatures and wetting, the risk column shows that infection conditions occurred May 5 and 7, and are predicted for May 10 and 11. High risks are shown for all of the other days between May 2 and May 12 with only wetting lacking for infection May 9 and 12. Because a spray application can serve as the wetting trigger, include streptomycin with spray applications May 8-12. Remember to protect young and recently planted trees, with flowers but considered to be "non-bearing".

The BBS column in the above graphic is tracking predicted symptom development for the first infection May 5, with 64% of the degree hours required for blossom symptom prediction. The CBS column indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which is predicted for May 8. 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/shoot blight situation due to hail injury, etc. To offset the potential for shoot tip infection in an active fire blight year such as this one, apply the plant growth regulator, prohexadione-calcium (Apogee, Kudos), at petal fall on king bloom. Shoot blight suppression results from hardening off of vegetative shoot growth starting about 10 days after the initial application.

Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is extreme for May 6, 7, and 10-12, and EIP infection conditions are shown for May 7, 10 and 11.
Graphic from Cougarblight, May 8, 2018. Click to enlarge.

Similar fire blight risks prevailed the past several days throughout areas of Virginia wherever susceptible bloom was present and wetting occurred. Although the length of wetting was more variable across the region and some areas did not receive the scab infection period, these areas still may have had enough wetting for fire blight infection.

Wednesday, May 2, 2018

Fire blight threat continues through the weekend

NOTE: Over the next couple days, apples will be near the peak of bloom in the Winchester area. Below are the fire blight risk assessments, comparing graphics from Maryblyt and also from the Cougarblight model as shown on our NEWA site, using the same weather data from our NEWA station to make these comparisons. 

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.
Graphic from Maryblyt 7, May 2, 2018. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program, with first bloom open Apr 14. The temperature and rainfall data are current through Wednesday evening, May 2. Predicted weather conditions are shown for May 3-8. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain, dew or a spray application), 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded temperatures and wetting, the risk column shows high risk for May 2-4 and May 7-8. With a forecast for rain during the weekend, infection conditions are shown for May 5-6, and only the wetting requirement is lacking for May 3-4 and May 8. Because a spray application can serve as the wetting trigger, include streptomycin with any spray application May 3-8. Streptomycin remains effective for only about three days under these conditions, so the ideal application timing for protection through the weekend would be May 4. Remember to protect young and recently planted trees, with flowers but considered to be "non-bearing".

Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is extreme for May 2-7, and EIP infection conditions are shown for  May 3-6.
Graphic from Cougarblight, May 2, 2018. Click to enlarge.
In general, similar fire blight risks prevail throughout areas in Virginia and probably much of the Mid-Atlantic region, wherever susceptible bloom is present, from late bloom in the southern areas, to early bloom in the more northern areas.

Powdery mildew has been very active the past week. Any “dry weather“ day above 53° is suitable for mildew infection. Since Apr 10 we have had 15 mildew infection days at our AREC.

Monday, April 30, 2018

High fire blight risk continues

NOTE: Many apple varieties in the Winchester area are approaching full bloom and should be near full bloom for this week's Shenandoah Apple Blossom Festival. Below are the fire blight risk assessments, comparing graphics from Maryblyt 7, and also from the Cougarblight model as shown on our NEWA site. We will be using the same weather data from our NEWA station to make these comparisons. We thank Dr. Mizuho Nita for hosting the Maryblyt 7.1 download site.

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.
Graphic from Maryblyt 7, April 30, 2018. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With first bloom open Apr 14. The temperature and rainfall data are current through Monday evening, April 30. Predicted weather conditions are shown for May 1-6. 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, dew or a spray application), 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded temperatures and wetting, the risk column shows high risk for May 2-6. Note that all of these conditions are met except for the wetting requirement. Because a spray application can serve as the wetting trigger, consider including streptomycin with any spray application May 1-6.

Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is extreme for May 2-6.
Graphic from Cougarblight, April 30, 2018. Click to enlarge.
A check of NEWA stations across Virginia shows that, in general, there will be similar extreme fire blight risks wherever bloom is present, southward in the Shenandoah Valley to Roanoke, and east of the Blue Ridge from Manassas to Danville.

Any “dry weather“ day above 53° is suitable for mildew infection. So far, since Apr 10 we have had at least 13 mildew infection days at our AREC.

Saturday, April 28, 2018

Fire blight alert

NOTE: Most apple varieties in the Winchester area are at early to mid-bloom. Below are the fire blight risk assessments, comparing graphics from Maryblyt 7, and also from the Cougarblight model as shown on our NEWA site. We will be using the same weather data from our NEWA station to make these comparisons. We thank Dr. Mizuho Nita for hosting the Maryblyt 7.1 download site.

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.
Graphic from Maryblyt 7, April 27, 2018. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With first bloom open Apr 14. The temperature and rainfall data are current through Friday evening, April 27. Predicted weather conditions are shown for April 28-May 3. 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded temperatures and wetting, the risk column shows high risk Apr 28, then declining to low to moderate risk for Apr 29-May 1, then high risk for May 2-3, when only the wetting requirement is lacking. Consider including streptomycin with any spray application May 1-3.

Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is high or extreme for May 2-3.

Wednesday, April 25, 2018

Heavy scab and rust infection period, Apr 24-25.

In Winchester, we recorded a heavy apple scab and rust infection period Apr 24-25: 30 hr at 47-56° (mean 51°), with 0.6 in. rain. Also, many cedar-apple rust and quince rust spores were released during this extended wetting period, and flowers are near their peak susceptibility for quince rust infection. In areas where there is a concern for rust infection, include an SI (DMI) fungicide in the next spray application. More wetting is expected Apr 26-27. 
Cedar apple rust galls with the spore horns fully expanded Apr 25, 2018.
Powdery mildew conidia have been available for infection at our AREC since Apr 10. Any “dry weather “ day above 53° is suitable for mildew infection. So far, we have had at least ten mildew infection days.
Fire blight: With continued predicted relatively cool temperatures in the, fire blight risk at Winchester should remain low or moderate through the weekend.

Apple scab infection conditions were similar to Winchester's southward in the Shenandoah Valley and east of the Blue Ridge, but with slightly warmer temperatures and with more than two inches of rain in some areas-- enough to erode the protective fungicide residue during the wetting event. 

Monday, April 23, 2018

Fire blight outlook this week

NOTE: Below are the fire blight risk assessments, comparing graphics from Maryblyt 7, and also from the Cougarblight model as shown on our NEWA site. We will be using the same weather data from our NEWA station to make these comparisons. We thank Dr. Mizuho Nita for hosting the Maryblyt 7.1 download site.

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.
Graphic from Maryblyt 7, April 23, 2018. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. We are using Wednesday, Apr 14 as the date of first bloom open on Idared and Pink Lady cultivars. The temperature and rainfall data are current through Monday evening, April 23. Predicted weather conditions are shown for April 24-27. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher, and this must coincide with an average daily temperature of 60°F or more. Based on recorded temperatures and wetting, the risk column shows low to moderate risk for Apr 23-27. With cooler predicted temperatures for the coming week or more, fire blight risk should remain low to moderate. However, with warmer than predicted temperatures, expect the risk to increase again.

Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” which also remains low at least through Apr 27.
 
Cougarblight graphic from April 23, 2018. Click to enlarge.
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 27.

Wednesday, April 18, 2018

Early threats by fire blight, apple scab and the rusts


NOTE: This year for fire blight risk assessment, we will be comparing and posting graphics from Maryblyt 7 as in previous years, and also from the Cougarblight model as shown on our NEWA site. We will be using the same weather data from our NEWA station to make these comparisons. We thank Dr. Mizuho Nita for hosting the Maryblyt 7.1 download site at: http://grapepathology.org/maryblyt 

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.
Maryblyt graphic April 18, 2018. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. We will use Saturday, Apr 14 as the date of first bloom open on Idared and Pink Lady cultivars at our AREC. The temperature and rainfall data are current through Wednesday evening, April 18. Predicted weather conditions are shown for April 19-22. 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, and this must coincide with an average daily temperature of 60°F or more. 

Based on recorded temperatures and wetting, the risk column shows high risk for Apr 15, with an EIP of 120 and wetting from rainfall, but with rapidly dropping temperatures, the daily mean was just 57.5°F. Entering an earlier bloom date raised the EIP for Apr 15, but did not raise the risk of infection if the daily mean temperature remained at 57.5°F. However, raising the daily mean for Apr 15 to 60°F did indicate infection. With cooler predicted temperatures for the coming week or more, fire blight risk should remain low to moderate. However, with warmer than predicted temperatures, expect the risk to increase again.

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 23.

Below is the graphic from the Cougarblight model as shown on our NEWA site. Note that we selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/14/2017. This date should be re-checked each time the site is accessed. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” which remains low at least through Apr 22. On the highest risk day, the EIP in Cougarblight was 113, comparable to the value of 120 shown for Maryblyt.
Cougarblight graphic April 18, 2018. Click to enlarge.
Scab and rust threats Apr 15-16: Fire blight is not the only disease that was marginally close to infection Apr 15. At our AREC, we recorded a wetting event of 18 hr at 41-47°, with 1.77 in. rain; ten of these hours at 41-42°. This amounted to 88% of the requirement for scab infection. Also, cedar-apple rust and quince rust spores were released during this wetting period, but it is not likely that rust infection occurred at these cool temperatures. However, where there is a concern for rust infection, it is wise to include an SI fungicide in the next spray application.

It was a different story farther south and east of the Blue Ridge, where more advanced bud stages and warmer temperatures Apr 15-16, resulted in likely infection by fire blight, apple scab and the rusts.

Friday, April 13, 2018

Rapid bud development; powdery mildew, scab and rust activity

The past two days we have seen rapid apple bud development in the Winchester area. Friday morning, Apr. 13, we saw heavy powdery mildew sporulation on Idared buds at tight cluster stage. Powdery mildew infects on dry days at temperatures above 53°F, so there were several infection days this week.
Powdery mildew on Idared, Friday morning, Apr. 13, 2018.
By Friday evening, many buds were showing color at the pre-pink stage. With warm temperatures over the weekend, expect open bloom by early next week.
Pre-pink stage of Idared buds Friday evening, Apr. 13, 2018
There is a forecast for thunderstorms and rain with temperatures in the 50s Sunday and into Monday, Apr 15-16, and that would bring a scab infection period as well as our first cedar-apple and quince rust infection period in the Winchester area. 
Cedar-apple rust gall with developing spore horns Apr. 11, 2018
 Generally, the forecast is similar for the areas south to beyond Roanoke and east of the Blue Ridge, with a trend toward earlier and a shorter wetting period, but with warmer temperatures to the south. In short, scab, the rusts, and powdery mildew are now active, and there is a potential for fire blight infection in more advanced areas with open bloom.

These conditions also favor cherry leaf spot and brown rot infection with cherry trees now in bloom, and brown rot and scab on peaches in bloom or petal fall stage.

Monday, April 2, 2018

It's time!

After delayed bud development through the last two weeks of March, we saw our first green tip on Red Delicious apples at our our AREC in Winchester last week Mar 27. Apple scab ascospores were released, and we recorded 49 hr of wetting at 35-47° F with 0.5 in. of rainfall from Mar 27-29. So this was an apple scab infection period where there was enough green tissue exposed during the wetting. Over the weekend, bud development advanced as far as 1/4-in. greentip on Red Delicious by Apr 2, as shown below. Last week's wetting conditions varied somewhat east of the Blue Ridge, but it is likely that scab infection could have occurred wherever the bud stage was more advanced, from Rappahannock southward to central Virginia.
Red Delicious apple buds at Winchester April 2.
Overwintering buds infected with powdery mildew were evident at Winchester by Apr 2, and it is expected that mildew spores will be released as leaf tissue in infected buds expands and 
the leaves unroll.
Idared apple bud infected with the powdery mildew fungus (right), compared with a healthy bud (left), Apr 2. Note weaker growth and reddish appearance of emerging tissues. There would have been no indication that this was an infected bud prior to budbreak.
Powdery mildew can infect developing blossoms at pink stage and cause the mildew-russet shown below. Mildew infection occurs with dry weather during temperatures above 53° F.
Net-like russet of Jonathan apple caused by mildew infection at pink stage.