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. 

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.

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.

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.

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.

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.

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.