Summer disease update

 Six extended wetting events since Jul 22 have dramatically increased summer disease pressures in the Winchester area: Jul 22: 6 hr wetting at 73° with 0.9 in. rain, Jul 23-24: 13 hr wetting at 73° with 0.51 in. rain, Jul 30-31: 21 hr wetting at 70° with 1.01 in. rain; Aug 1-2: 15 hr wetting at 72° with 0.45 in. rain, Aug 3-4: 19 hr wetting at 68° with 0.92 in. rain; and Aug 6: 6 hr wetting at 68° with 0.2 in. rain. Suffice it to say that Winchester's extended dry conditions of July have passed! Wetting events at these temperatures have favored development of sooty blotch and flyspeck and the rot fungi. Evidence of early season (scab), mid-season (Brooks spot), and late season diseases (sooty blotch and developing rots) is shown below:

Scab, sooty blotch and rot spots on unprotected Granny Smith fruit at Virginia Tech AREC, Winchester, VA, Aug 10, 2020.

Infection by Brooks spot (8 o'clock and 1 o'clock positions from the calyx), as well as sooty blotch and rot spots on unprotected Idared fruit, Aug 10, 2020. Infection by Brooks spot, one of the earliest "summer diseases", typically occurs about a month after petal fall.

Recent disease pressure has been somewhat heavier than Winchester in other areas of Virginia, especially east of the Blue Ridge. Amounts of rainfall from extended wetting events have varied, especially with the remnants of the recent hurricane. Most were not excessive in areas where rain was needed; some extended wetting occurred with only a few hundredths of an inch of rainfall. All of these have been favorable for rot development where protection was inadequate and volume of rainfall can impact fungicide residual. 

Fire blight-killed shoots harbor the rot fungi and are a common pre-harvest inoculum source. Due to cool temperatures throughout bloom, the Winchester area mostly escaped fire blight this year, but infection was more common east of the Blue Ridge and in the Roanoke area.

Accumulated wetting hours through the summer can be an indicator of summer disease pressure, particularly to predict the development of the sooty blotch and flyspeck (SBFS) fungal complex, but also can be a general indicator of rot pressure. To predict SBFS, we record accumulated wetting hours (ACW) from rainfall, fog, or dew, starting 10 days after petal fall. The action threshold of 250 ACW predicts that the SBFS fungi are present on unprotected fruit when the threshold is reached, and symptoms will soon appear with further incubation. Winchester passed the 250-hr threshold on July 21, and symptoms are now present on unprotected fruit, as shown above, with symptoms heavier at lower elevations, which have more wetting hours. Here is a listing of selected petal fall dates and current total wetting hour accumulation (ACW) for selected locations as of Aug 10: Winchester, May 5, 393 ACW; Staunton, May 5, 823 ACW; Roanoke, Apr 18, 447 ACW; Floyd, Apr 28, 470 ACW; Manassas, Apr 28, 694 ACW; Sperryville, Apr 28, 387 ACW; Crozet, Apr 18, 423 ACW; Carter Mountain, Apr 18, 558 ACW; Red Hill, Apr 18, 483 ACW; Lynchburg, Apr 13, 647 ACW; Rustburg, Apr 13, 573 ACW; Danville, Apr 13, 832 ACW. 

Unless unusual fruit disease-related events occur, this will be the final post for this year. With approaching harvest, carefully observe pre-harvest intervals and per acre per year restrictions for all fungicides and all crop protection products.

Fire blight infection conditions on late bloom May 15; scab and rust infection May 14-15.

Fire blight infection conditions finally occurred at Winchester on late bloom May 15. Below is a cropped graphic from the Maryblyt 7 program.

Graphic from Maryblyt 7, May 18, 2020. Click to enlarge.

While most apple blocks were past bloom in the Winchester area, a few still had some susceptible bloom. The temperature and rainfall data are current through Monday evening, May 18. Predicted weather conditions are shown for May 19-31. 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 the infection was possible wherever bloom was present May 15. Infection aslo would have been possible with wetting May 16-17. The extended outlook through May 31 is shown primarily to track infection development from May 15, but indicates that infection would be possible wherever there is bloom and wetting May 27-31.

The BBS column tracks the appearance of blossom blight symptoms from infection that occurred May 15, which is now predicted for May 27. The CBS column tracks canker blight symptom appearance and predicted canker margin symptoms (CMS, expansion of overwintered cankers) May 16. Further tracking in the CBS column predicts canker blight symptoms when that value reaches 100 May 28.

Under these conditions a Streptomycin application would have been recommended for May 14-15, to protect any late bloom through the infective period. This would particularly include any young and recently planted trees with flowers. Cooler predicted temperatures the next week indicate a decline in risk, but warmer temperatures will again bring the EIP to an infective level May 26. Note that "wetting" can occur with maintenance and thinning applications, so streptomycin should be included in such applications if there is late bloom. Also note that, while bloom may have escaped infection during this unusually low fire blight pressure year at Winchester, expect canker blight and shoot blight symptoms if cankers were allowed to overwinter in trees that had infection last year.

At the AREC last week an apple scab and cedar-apple rust infection period occurred May 14-15: 8 hr wet at 62° with 0.04 in. rain. Similar conditions also extended south to Staunton and east of the Blue Ridge from Manassas to Sperryville. Staunton and Sperryville to the Charlottesville area also had an infection period May 17. At Winchester, cedar-apple rust galls remain active after this wetting event with only 0.04 inches of rain.

Apple powdery mildew infection occurs on days without rainfall above 53°, and in the Winchester area we have had 16 days favorable for infection since spores were available on Mar 29. Secondary mildew symptoms are now quite common on unprotected trees, as are secondary scab and cedar-apple rust lesions.

Extended wetting is predicted for all major fruit production areas in Virginia May 18-22. This wetting will be highly favorable to secondary scab and late rust infection on foliage and will contribute to recorded accumulated wetting hours for development of sooty blotch and flyspeck (SBFS). For purposes of predicting the development of the SBFS fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. This year we will use May 5 as the petal fall date for Winchester, so the start of wetting hour accumulation (ACW) will be from May 15. For the Roanoke area and areas east of the Blue Ridge, we will consider petal fall to have been one week earlier than Winchester, and accumulation of wetting hours will be from May 8. The action threshold for SBFS development is 250 ACW.

Secondary apple scab and rust infection periods April 28 through May 4; fire blight pressure low to moderate in the Winchester area

At Winchester, most apple trees are at petal fall and only later varieties such as Rome Beauty and some young trees are still in bloom. 

At the AREC in the past week we received three apple scab/rust infection periods.  Apr 28: 9 hr wet at 49° with 0.06 in. rain; Apr 29-30: 19 hr wet at 58° with 1.22 in. rain (heavy scab and rusts) and May 3-4: 7 hr wet at 62° with 0.42 in. rain. Cedar-apple rust galls and quince rust cankers remain active after these wetting events, and unprotected apple blossoms and small fruit remain susceptible to quince rust infection, so a follow-up application including an SI fungicide is suggested. On May 4 cedar rust lesions were evident on flower cluster and shoot leaves, from infection that occurred Apr 7-8.

This past week the length of wetting and amounts of rainfall have been somewhat variable across the major commercial fruit production areas of Virginia, but all areas received at least one extended wetting period favorable to secondary scab infection where control was not achieved during earlier primary infection periods. 

Apple powdery mildew infection occurs on days without rainfall above 53°, and we have had 12 days favorable for infection since spores were available on Mar 29. Expect secondary powdery mildew symptoms to begin appearing in the next week or so.

In the Winchester area, fire blight pressure has been mostly low to moderate on apples that first bloomed Mar 30, and that trend continues for late blooming apples through the coming week, However, fire blight blossom symptoms were reported on early blooming Asian pears Apr 27 in Clarke County. Also blossom infection (shown below) was also evident in young apple trees in central Virginia, apparently from infection that occurred Mar 29.

Blossom blight symptoms in central VA, May 2, 2020. Infection probably occurred Mar 29.

Apple scab and rust infection Apr 23-27; fire blight blossom symptoms reported on early blooming Asian pears in Clarke Co.

At Winchester, Red Delicious apple trees are near petal fall, but there is still much bloom on many apples, and later varieties such as Rome Beauty are now in full bloom. At the AREC we received two recent infection periods.  Apr 23-24: 21 hr wet at 50° with 0.41 in. rain (scab and rusts); Apr 25-27: 31 combined hr wet at 47° with 0.80 in. rain. Cedar-apple rust galls and quince rust cankers were in "full bloom" during these extended wetting events, and unprotected apple blossoms remain very susceptible to quince rust infection, so a follow-up application including an SI fungicide is suggested. On Apr 27 a few cedar rust lesions were evident on flower cluster leaves, from infection that occurred Mar 27-28.

The above conditions for Winchester were generally similar across most of the major commercial fruit production areas of Virginia. The greatest concerns for these events are where earlier infection periods occurred with inadequate fungicide protection, and scab lesions are now sporulating, leading to heavy secondary infection.

Apple powdery mildew infection occurs on days without rainfall above 53°, and we have had ten days favorable for infection since spores were available on Mar 29. Expect secondary powdery mildew symptoms to begin appearing in the next week or so.

Although fire blight pressure has been mostly low to moderate on apples that first bloomed Mar 30 in the Winchester area, fire blight blossom symptoms on early blooming Asian pears were reported Apr 27 in Clarke County. In that case, apparently the pear trees were in bloom by Mar 19 and infection likely occurred on Mar 20, before the first apple blossoms were open at our AREC.

Fire blight pressure low to moderate through April 25; secondary scab infection possible where control was inadequate Mar 27-28.

At Winchester apple trees are mostly at mid-bloom. 

Fire blight: With prevailing cool temperatures, current fire blight pressure remains low to moderate through Apr 25 in the Winchester area, the Shenandoah Valley, and across much of northern Virginia. Conditions through Apr 25 are not favorable for fire blight infection in the Roanoke and east of the Blue Ridge south of Charlottesville, however some of these areas had earlier potential infection Mar 28-31 and Apr 7-9.

Scab: At the AREC we received a marginal apple scab infection period Apr 17-18: 14 hr wet at 47° with 0.08 in. rain. Most of the scab ascospores have been discharged signalling the end of the primary infection, but where protection was inadequate during the Mar 27-28 infection period, expect lesions to be appearing, and secondary infection could be possible with predicted wetting events later this week.
   
At Winchester, we have had 12 days favorable for apple powdery mildew infection since spores were available.

This will be updated again Apr 28.

This week's fire blight outlook for Winchester and beyond

NOTE: This year for fire blight risk assessment, I will post a graphic from the Cougarblight model as shown on our NEWA site. I will be using the same weather data from our NEWA station to make a comparison to Maryblyt 7 as in previous years, but not posting the MaryBlyt graphic. 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.

Graphic from Cougarblight, April 6, 2020. Click to enlarge.

FIRE BLIGHT: Above 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 3/30/20. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is low or caution for this week Apr 7-11. The Roanoke area and areas east of the Blue Ridge south of Charlottesville have a potential for infection Apr 7-9 (graphics not shown). Setting the first bloom date to 3/25/20 instead of 3/30/20 did not make any difference in prediction of infection for this week. However, Roanoke and areas south of Charlottesville could have had earlier infection (March 27-31) if the first bloom date had been as early as March 20.

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, which occurs with wetting. The fire blight outlook will be updated Apr 13.

Heavy scab and rust infection, May 3-6

We recorded two heavy apple scab and rust infection periods at Winchester over the weekend: May 3-4 (19 hr wet at 64° with 0.4 inches of rain) and May 4-5 (more than 21 hr wet at 62° with 2.18 inches of rain). The last wetting period, with heavy rainfall, is still in progress. This amount of rainfall depleted any fungicide residue applied last week, resulting in potentially heavy rust and scab infection to foliage and fruit. A follow-up fungicide application with after-infection activity is suggested.

Also, we have had 18 days favorable for powdery mildew infection since spores were available at Winchester Apr 6. The fire blight outlook for Winchester remains much as indicated in the post on May 2: the risk of infection remains high wherever there is late bloom present.

Fire blight outlook 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. Fruit producers in other areas are encouraged to consult their state extension specialists for information similar to that provided here.

Graphic from Maryblyt 7, May 1, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. We have moved through bloom in a timely fashion in the Winchester area, but many apple blocks still have some susceptible bloom. The temperature and rainfall data are current through Wednesday evening, May 1. Predicted weather conditions are shown for May 2-6. 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 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 the infection was possible Apr 19 and 25, and was possible with wetting Apr 18, 23 and 24, and will again be possible with wetting May 2-4. The temperature is marginally close for infection May 5. The extended outlook May 6 through May 10 (not shown) indicates infection is possible wherever there is bloom and wetting through May 10.

Streptomycin application is recommended for tomorrow, May 2, to protect any late bloom into the weekend. Also, remember to protect any young and recently planted trees that have flowers. Predicted temperatures into next week (not shown) indicate that infection will remain possible wherever there is late bloom and wetting every day next week. Note that "wetting" can occur with maintenance and thinning applications, so streptomycin should be included in such applications where there is late bloom. 
The BBS column tracks the appearance of blossom blight symptoms from infection that occurred Apr 19, which is now predicted for May 3. The CBS column is tracking canker blight symptom appearance and predicts canker margin symptoms (CMS, expansion of overwintered cankers) is predicted May 1. Further tracking in the CBS column will predict canker blight symptoms when that value reaches 100.

Below is the graphic from the Cougarblight model as shown on our NEWA site. with “Fire blight occurred in your neighborhood last year” selected as the orchard blight history option and first blossom open date as 4/13/2019. Cougarblight shows color-coded risk assessments as “Cougarblight 4-Day DH” and infection potential EIP value. This risk is "extreme" for May 2-6, with infection possible if wetting occurs May 2-4. The average temperature of 60 F is lacking for May 5.

Graphic from the NEWA/Cougarblight model, May 1, 2019. Click to enlarge.

Fire blight risks can change quickly with warmer than predicted temperatures and wetting; in high-risk situations, a streptomycin application is more effective when applied ahead of predicted infection. Unless unexpected weather conditions arise, this will be the last fire blight update for this season.

Fire blight outlook Apr 29-May 4; secondary scab infection Apr 27-28.

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. Fruit producers in other areas are encouraged to consult their state extension specialists for information similar to that provided here.

Graphic from Maryblyt 7, April 29, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most apple trees still have susceptible bloom in the Winchester area. The temperature and rainfall data are current through Sunday evening, April 28. Predicted weather conditions are shown for April 29-May 4. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). 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 the infection was possible Apr 19 and 25, and would be possible with wetting Apr 18, 23 and 24, and will again be possible with wetting May 1-4. 
Streptomycin application is recommended for tomorrow, Apr 30 or Wednesday, May 1 to protect late bloom into the weekend. Also, remember to protect any young and recently planted trees that have flowers. Predicted temperatures into next week (not shown) indicate that infection will remain possible wherever there is late bloom and wetting every day next week. Note that "wetting" can occur with maintenance and thinning applications, so streptomycin should be included in such applications while late bloom is present. The BBS column tracks the appearance of blossom blight symptoms from infection that occurred Apr 19, which is predicted for May 2. The CBS column is tracking canker blight symptom appearance and predicts canker margin symptoms (CMS, expansion of overwintered cankers) is predicted Apr 30.

Below is the graphic from the Cougarblight model as shown on our NEWA site. with “Fire blight occurred in your neighborhood last year” selected as the orchard blight history option and first blossom open date as 4/13/2019. Cougarblight shows color-coded risk assessments as “Cougarblight 4-Day DH” and infection potential EIP value. This risk is "extreme" for May 1-4 with infection possible if wetting occurs. 

Graphic from the NEWA/Cougarblight model, April 29, 2019. Click to enlarge.

Note that real fire blight risks can change quickly with warmer than predicted temperatures and wetting and, in high-risk situations, a streptomycin application is more effective when applied ahead of predicted infection.

We recorded a secondary apple scab infection period at Winchester Apr 27-28: 13 hr wet at 50° with 0.16 inches of rain. This would have been a secondary infection period where scab was not well controlled during the Apr 5-6 infection, resulting in scab lesions with spores now available for secondary infection. 

Fire blight infection possible April 25

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

Graphic from Maryblyt 7, April 24, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Apple trees are near full bloom in the Winchester area. The temperature and rainfall data are current through Tuesday night, April 23. Predicted weather conditions are shown for April 24-28. 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 the infection was possible Apr 19 and 25, and would be possible with wetting Apr 18, 23 and 24. Streptomycin is recommended to be applied today or tomorrow, Apr 24 or 25, and for any regular spray application when wetting is the only factor lacking for infection. Also, remember to protect young and recently planted trees, which have flowers but might be considered to be "non-bearing". Fire blight risk should subside with cooler predicted temperatures Apr 26-28. The BBS column is tracking the appearance of blossom blight symptoms from infection that occurred Apr 19. Symptom appearance is predicted when this value reaches 100.

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 4/13/2019. Cougarblight shows color-coded risk assessments as “Cougarblight 4-Day DH” and infection potential EIP value. This risk is "high" for Apr 23, 24 and 26 and "extreme" or infection tomorrow, Apr 25, and also with infection possible with a trace of wetting from rainfall today, Apr 24, so the current predictions are similar for the Cougarblight and Maryblyt models. 

Graphic from the NEWA/Cougarblight model, April 24, 2019. Click to enlarge.

Note that real fire blight risks can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a streptomycin application is more effective when applied ahead of predicted infection.

Apple scab and rust infection Apr 19-20; fire blight outlook this week

We recorded another apple scab and rust infection period at Winchester Apr 19-20: 13 hr wet at 62° with 1.01 inches of rain. Considering the timing of this infection period while flowers are highly susceptible to quince rust infection, it is prudent to include an SI  fungicide for after-infection control of rusts in the next spray application. Similar wetting and temperature conditions occurred east of the Blue Ridge and southward to Roanoke and beyond. Such conditions were also favorable for infection by peach scab on small fruits which are now vulnerable after the "shuck-split" stage.
Also, we have had 9 days favorable for powdery mildew infection since mildew spores were available Apr 6.

Fire blight outlook for Winchester: Below is a cropped graphic from the Maryblyt 7 program. Apple trees are now near full bloom in the Winchester area. The temperature and rainfall data are current through Sunday evening, April 21. Predicted weather conditions are shown for April 22-26. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). 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. 

Graphic from Maryblyt 7, April 22, 2019. Click to enlarge.

Based on recorded temperatures and wetting, the risk column shows that infection was possible Apr 19. and risk remained high high for Apr 20, but subsided Apr 21-22. Note that the EIP is near 100 or above for Apr 23-26, so a slight increase in temperature or wetting this week could change the risk factors that are lacking (EIP of 100, average temperature of 60,wetting). As it stands, a special caution is in order for Apr 25 when only wetting is lacking for infection. Because any spray application can serve as the wetting trigger, include streptomycin with any spray applied under such conditions through late bloom. Also, remember to protect young and recently planted trees, which may have flowers but might be considered to be "non-bearing". The BBS column is tracking the appearance of blossom blight symptoms from infection that occurred Apr 19. Symptom appearance is predicted when this value reaches 100.

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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH”. This risk is "caution" for Apr 22 and "high" for Apr 23-26. Note that if we were to select "Fire blight is now active in your neighborhood" as the orchard blight history, "caution" becomes "high" and "high" becomes "extreme".  The difference in EIP level shown for Apr 20 in this graphic compared to the Maryblyt graphic above is related to the temperatures that were entered on Apr 18-19 (not shown in the Cougarblight graphic). 

Graphic from Cougarblight, April 22, 2019. Click to enlarge.

Note that real fire blight risks can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

Possible fire blight, scab and rust infection today

NOTE: This year for fire blight risk assessment, we are again comparing posted graphics from Maryblyt 7, as in previous years, with those from the Cougarblight model as shown on our NEWA site. We will be using the same recorded 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, April 19, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most cultivars are now have bloom with some near full bloom in the Winchester area. The temperature and rainfall data are current through Friday morning, April 19. Predicted weather conditions are shown for April 19-23. 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, 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 13 and 16, but with an EIP less than 100; by Apr 18 the EIP reaches 100, but wetting is lacking. Apr 19 shows a significant risk of infection with all infection criteria met. For such situations a spray of streptomycin is recommended by Apr 19. With cooler temperatures Apr 20-22 risk should subside, but will again begin to increase with warmer temperatures Apr 23. The BBS column in the Maryblyt graphic is tracking the appearance of blossom blight symptoms from infection that occurs today, Apr 19. Symptoms appearance is predicted when this value reaches 100.

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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is "caution" for Apr 18 and "high" for Apr 19-22. This is a rather important difference between the two predictive models. Note that this graphic would indicate "extreme" risk if today's EIP were 100, but it is 99, not quite triggering the "extreme" risk. Caution: Both of these models are a guide to fire blight risk, and the EIP shown in the graphic below is very close to infection conditions with rain today Apr 19. 

Graphic from Cougarblight 7, April 19, 2019. Click to enlarge.

Risk can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Apr 22.

Also note that apple scab, cedar-apple rust and quince rust infection are likely today, with locally heavy rainfall expected during the day and continued wetting through tonight.

Powdery mildew is now active. Mildew conidia have been available for infection at our AREC since Apr 6. Any “dry weather“ day above 53° is suitable for mildew infection, and we have had seven mildew infection days since Apr 6.

Increasing fire blight threat Apr 18-19!

NOTE: This year for fire blight risk assessment, we are again comparing posted graphics from Maryblyt 7, as in previous years, with those from the Cougarblight model as shown on our NEWA site. We will be using the same recorded 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.

Graphic from Maryblyt 7, April 17, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most cultivars now have some bloom open in the Winchester area. The temperature and rainfall data are current through Wednesday evening, April 17. Predicted weather conditions are shown for April 18-22. 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 13 and 16, but with an EIP less than 100; by Apr 18 the EIP reaches 100, but wetting is lacking. Apr 19 shows a significant risk of infection with all infection criteria met. For such situations a spray of streptomycin is recommended on Apr 18 or 19. Cooler temperatures Apr 20-22 should reduce fire blight risk.

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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is "caution" for Apr 18 and "high" for Apr 19-22. This is a rather important difference between the two predictive models. The apparent unusual difference in amount of risk predicted by Maryblyt and Cougarblight is because the EIP does not reach 100 (only 85) in Cougarblight but in Maryblyt it is 103 on Apr 18 and 116 on Apr 19 due to higher daily average temperatures, especially for Apr 18.

Graphic from Cougarblight, April 17, 2019. Click to enlarge.

Risk can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Apr 19.

Fire blight outlook at Winchester this week

King bloom on Idared, Apr 14, 2019.

NOTE: This year for fire blight risk assessment, we will again compare posted 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.

 

Graphic from Maryblyt 7, April 14, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. We will use Saturday, Apr 13 as the date of first bloom open on early cultivars such as Idared and Pink Lady. The temperature and rainfall data are current through Sunday evening, April 14. Predicted weather conditions are shown for April 15-20. 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, 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 13, 15, and 16, but lacks the required EIP of 100. Entering an earlier bloom date did not raise the EIP for Apr 13, and did not raise the risk of infection. With cooler predicted temperatures mid- week, fire blight risk should be low to moderate Apr 17-18. 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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is low for Apr 14-16.

Graphic from Cougarblight, April 14, 2019. 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 Apr 17.

Apple scab infection April 5-6.

The first general apple scab infection occurred in the Winchester area and east of the Blue Ridge from Rappahannock County and south to Lynchburg April 5-6. At our AREC in Winchester, scab ascospores were released, and we recorded 33 hr of wetting at 40-47° F with 0.5 in. of rainfall. Many apple cultivars such as Cripps Pink, Red Delicious, Gala (shown below), and Idared are in the tight cluster stage, and presented a sizable target of exposed green tissue for scab infection. Hopefully, there was opportunity to apply protective fungicides prior to this infection.

Gala apple buds at tight cluster stage at Winchester 4/6/19.

Cedar-apple rust gall spore horns (shown below)  are expanding and will probably discharge the basidiospores that infect apple with the next wetting period. By tight cluster stage powdery mildew spores are usually available for infection, which occurs on dry days above 53° F

Cedar-apple rust gall at Winchester 4/6/19

Where the bud stage is more advanced to pink or open blossoms, as in central Virginia and the Roanoke area and south, be alert for fire blight infection with warmer weather and shower or thunderstorm activity this week.