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.

Extended wetting events and accumulated wetting hours favor early rot development

Two extended wetting events at Winchester last week favored secondary apple scab and cedar-apple rust infection and early rot development.  These occurred June 4-5: 17 hr of wetting at 69° with 0.83 in. rain and June 5-6: 18 hr of wetting at 69° with 0.42 in. rain. Wetting was variable across other commercial fruit production areas of Virginia. Apple powdery mildew infection occurs on days without rainfall above 53°, and the Winchester area we have had 33 days favorable for infection since spores were available on Mar 29.

To predict the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (ACW) from rainfall or dew, starting 10 days after petal fall. The action threshold for SBFS development is 250 ACW. Here is a listing of selected petal fall date and total wetting hour accumulation (ACW) for selected locations as of June 9: Winchester, May 5, 112 ACW; Staunton, May 5, 217 ACW; Roanoke, Apr 18, 205 ACW; Floyd, Apr 28, 188 ACW; Manassas, Apr 28, 182 ACW; Sperryville, Apr 28, 146 ACW; Batesville, Apr 18, 208 ACW; Crozet, Apr 18, 178 ACW; Carter Mountain, Apr 18, 314 ACW; Red Hill, Apr 18, 189 ACW; Lynchburg, Apr 13, 243 ACW; Rustburg, Apr 13, 247 ACW; Danville, Apr 13, 331 ACW. 

ACW is related to wetting from rainfall, fog, or dew. The action threshold of 250 ACW signals that the SBFS fungi would be present on unprotected fruit when the threshold is reached and symptoms would appear with further incubation. Carter Mountain and Danville have passed the threshold, and Lynchburg and Rustburg are close to the threshold.  

Extended wetting events and accumulated wetting hours predict the development of sooty blotch and flyspeck

At Winchester last week a secondary apple scab and cedar-apple rust infection period occurred May 28: 7 hr of combined wetting at 69° with 0.09 in. rain. Most of the other commercial fruit production areas of Virginia experienced similar conditions, with relatively warm extended wetting during the period from May 27 to 29. Expect extended wetting events with warmer temperatures to increase the potential for early latent rot infection of fruit. At Winchester,  cedar-apple rust galls remain active. Apple powdery mildew infection occurs on days without rainfall above 53°, and in the Winchester area we have had 29 days favorable for infection since spores were available on Mar 29.

To predict the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (ACW) from rainfall or dew, starting 10 days after petal fall. The action threshold for SBFS development is 250 ACW. Here is a listing of selected petal fall date and total wetting hour accumulation (ACW) for selected locations: Winchester, May 5, 73 ACW; Staunton, May 5, 167 ACW; Roanoke, Apr 18, 194 ACW; Floyd, Apr 28, 174 ACW; Manassas, Apr 28, 131 ACW; Sperryville, Apr 28, 114 ACW; Batesville, Apr 18, 186 ACW; Crozet, Apr 18, 162 ACW; Carter Mountain, Apr 18 329 ACW; Red Hill, Apr 18, 175 ACW; Lynchburg, Apr 13, 226 ACW; Rustburg, Apr 13, 235 ACW; Danville, Apr 13, 288 ACW. 

The action threshold of 250 ACW signals that the SBFS fungi would be present on unprotected fruit when the threshold is reached and symptoms would appear with further incubation. Carter Mountain and Danville have already passed the threshold, and Lynchburg and Rustburg may reach the threshold within the coming week . ACW is related to wetting from rainfall or dew, and typically, lower elevations in an orchard accumulate wetting hours more quickly because of wetting from dew. So far this year, that was not the case with the higher elevation of Carter Mountain accumulating wetting hours more rapidly from extended wetting from rainfall and fog in the past two weeks.

Extended wetting last week will trigger early summer disease development

At the AREC last week an apple scab and cedar-apple rust infection period occurred May 22-23: 24 hr of combined wetting at 60° with 1.14 in. rain. Conditions were similar east of the Blue Ridge in Manassas and Sperryville, but more extreme to the south from Staunton to Roanoke and Floyd and east of the Blue Ridge from the Charlottesville area southward to Lynchburg and Danville. At Winchester, cedar-apple rust galls remain active with more extended wetting periods predicted for this week.

Staunton had two wetting periods of 10 and 42 hr with a total of 0.91 in. rain. In Roanoke, two infection periods totaled 113 hr combined wetting and 10.17 in. rain. The total rainfall in Floyd was 1.92 inches, but with 115 hr of extended wetting. In Albemarle County, combined wetting ranged from 43-55 hr at Crozet, Red Hill and Batesville to 102 hr on Carter Mountain with rainfall totals from 1.3 to 2.6 inches. Lynchburg had 86 hr wetting with 2.95 in rain, Rustburg 114 hr wet with 3.87 in. rain and Danville 89 hr combined wetting with 4.69 in. rain.

In all areas, this extended wetting will contribute to early accumulation of wetting hour totals toward development of sooty blotch and flyspeck. Fortunately, much of the earlier portion of the wetting events was at cooler temperatures not as favorable to rot development, but the latter portion was at warmer temperatures, and occurred after heavy rains would have depleted fungicide residue, making the fruit vulnerable to latent rot infection. This extended wetting was also favorable to secondary scab and late rust infection on foliage, and the extremely long wetting periods can increase the amount of fruit scab.

For purposes of predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (ACW) from rainfall or dew, starting 10 days after petal fall. The action threshold for SBFS development is 250 ACW. Here is a listing of selected petal fall date and total wetting hour accumulation (ACW) for selected locations: Winchester, May 5, 55 ACW; Staunton, May 5, 133 ACW; Roanoke, Apr 18, 174 ACW; Floyd, Apr 28, 159 ACW; Manassas, Apr 28, 91 ACW; Sperryville Apr 28, 102 ACW; Batesville Apr 18, 164 ACW; Crozet, Apr 18, 138 ACW; Carter Mountain, Apr 18 329 ACW; Red Hill, Apr 18, 150 ACW; Lynchburg, Apr 13, 199 ACW; Rustburg, Apr 13, 201 ACW; Danville, Apr 13, 243 ACW. The action threshold of 250 ACW means that the SBFS fungi would be present on unprotected fruit when the threshold is reached. Lynchburg, Rustburg and Danville are predicted to reach the threshold within the coming week and Carter Mountain has already passed the threshold. ACW is related to wetting from rainfall or dew, and often lower elevations in an orchard accumulate wetting hours more quickly because of wetting from dew, but that obviously is not the case with the higher elevation of Carter Mountain this year.

Apple powdery mildew infection occurs on days without rainfall above 53°, and in the Winchester area we have had 26 days favorable for infection since spores were available on Mar 29. 

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.

Summer diseases and powdery mildew; Pre-harvest apple disease outlook in the Winchester area

In the past month we recorded only two major extended wetting events at our AREC in Winchester: Jul 22-23 (18 hr wet at 68° with 2.74 in. rain) and yesterday, Aug 13-14 (14 hr wet at 72° with 0.5 in. rain). However, there were also nine other wetting events less than 5 hr in length, with relatively small amounts of rainfall, and some of those may have had greater amounts of rainfall and stayed wet longer in surrounding areas. 

Due to comparatively delayed wetting hour accumulation this year, sooty blotch was slower to make its appearance, and was first observed at our AREC last week (shown below).

Sooty blotch (and scab) observed on unprotected Fuji apples August 8, 2019.

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 chose May 2 as the petal fall date for Winchester, so the start of wetting hour accumulation (ACW) was from May 12. As of Aug 14, total wetting hour accumulation by our AREC NEWA weather station was 342 hr and the 250-hr action threshold was reached Jul 11. In 2017 by Aug 14 we had recorded 462 ACW, the threshold was reached July 5 and SBFS was observed July 7. By contrast, during the extremely wet year last year (2018), we saw 630 ACW by Aug 14, the 250-hr threshold was reached June 12, and SBFS was observed by June 27.

In trees not protected by fungicides this year, bitter rot is more common than SBFS, indicative of early summer disease pressure in May and June.

Powdery mildew on late shoot growth: As frequently occurs following heavy rains after a dry period, the 2.7 inches of rain Jul 22-23, promoted a flush of renewed late season growth that was very susceptible to mildew (see below). 

Powdery mildew on late season growth, Granny Smith apple, July 31, 2019

Late infection often leads to a lot of mildew carryover in buds, and a recurrent problem and a significant reduction in yield the next year. This is particularly true with very susceptible varieties like Granny Smith, Idared, Ginger Gold and Honeycrisp, and in situations like this, it is prudent to select late-season fungicides with mildew activity as well as rot and SBFS activity. Examples include products such as Merivon, Luna Sensation, Pristine, Inspire Super and Indar. Caution: Remember to observe allowed pre-harvest intervals for all fungicides as well as insecticides and other products.

Increasing summer disease pressures

Summer disease pressures have increased in the past two weeks. At our AREC in Winchester, we recorded three extended wetting events since the last post Jul 6: Jul 5-6 (13 hr wet at 73° with 0.06 in. rain; Jul 8 (7 hr wet at 73° with 0.12 in. rain); and Jul 11 (8 hr wet at 79° with 0.63 in. rain). Infection by the bitter rot and white rot fungi will occur quickly with wetting and temperatures in the 70s.

The image below, sent to me from the Winchester area, suggests increasing rot pressures.

Rots with mummies. (Photo by W. Mackintosh).

The proximity and distribution of the spots to the mummies suggests that they are developing rots. Some spots were described as having droplets on them. The explanation is that it is probably droplets splashed off the mummies, carrying spores and other dark juicy material. Some droplets carrying spores may incite rot infection and others may not, or some might stay latent for a period of time. Some rots might just be growing slower than others so they get over run by the faster growing organism.

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 chose May 2 as the petal fall date for Winchester, so the start of wetting hour accumulation (ACW) was from May 12. Wetting hour accumulation in July has brought the total ACW to 273 hr, (past the 250-hr action threshold). ACW at Roanoke remains similar to Winchester at 269 hr, but with only 0.36 in. rainfall in July.

Other areas of Virginia with (ACW total) and rainfall in July are: Staunton (452 hr, 1.40 in.); Rappahannock County (Gadino Cellars, 362 hr, 3.06 in. rain); Red Hill (878 hr, 0.24 in.); Lynchburg (552 hr, 1.54 in,); Floyd (362 hr, 1.66 in.); Danville (649 hr, 2.53 in. rainfall). 

Recent extended wetting; early summer disease pressures June 2, 2019

At our AREC in Winchester we recorded two extended wetting events: May 26-27, with 6 hr of wetting at 69° with 0.15 in. rain; and June 2, with 9 hr of wetting at 61° with 0.2 in. rain. Again these extended wetting events 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 chose May 2 as our petal fall date for Winchester, so the start of wetting hour accumulation was from May 12. As of 8 AM June 2, accumulated wetting hours (ACW) already passed the 250 wetting hour threshold for specific treatment against the SBFS fungal complex: at 909 ft elevation we had 331 hr; at 932 ft (the AREC NEWA station), 93 hr; and at the 983 ft elevation, 90 hr ACW. One of the purposes of following three weather stations is to compare wetting hour accumulation at different elevations. Note that we have already passed the threshold at the lower elevation and the total is more than 100 hr ACW more than last year on this date. At the two higher elevations ACW accumulation is more than 100 less than last year at this time. NOTE: Edited Jun 12: Last week we discovered an error with the sensor at the lower elevation, 909 ft, which had already accumulated 331 hr ACW; that figure was distorted because the wetness sensor had come loose from its stand and dropped into the grass where it remained wet abnormally long.

The sooty blotch/flyspeck model on NEWA indicates accumulated wetting similar to the ACW shown at our NEWA station. To use this model, select a weather station, go to the drop-down menu for diseases and enter the petal fall date (e. g. May 2) to calculate the risk for that location.

Sooty blotch/flyspeck risk summary for Winchester AREC, 932 ft elevation, using May 2 as petal fall date.

For central Virginia, we selected Apr 23 as the petal fall date for accumulation of wetting hours by selected weather stations. As of June 2, Red Hill had 349 ACW (also past the threshold). Lynchburg  had 240  ACW. Also east of the Blue Ridge, the NEWA station at Batesville  has 109 ACW, while the NEWA station at Gadino Cellars near Washington, VA has recorded 150 ACW with Apr 29 as the petal fall date. 

Sooty blotch /flyspeck, bitter rot and Glomerella leaf spot activity

In the last week at  our AREC in Winchester we recorded two more extended wetting events: June 27-28, with 9 hr of wetting at 70° with 0.06 in. rain; July 4-5, with 15 hr of wetting at 70° with 1.27 in. rain. These wetting events favored early summer disease and rot activity on apples, peach scab, and cherry leaf spot and brown rot on ripening stone fruits. 

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 (from May 17 at Winchester). As of 6 AM July 5, AREC weather stations at three elevations had accumulated more than 110 hr beyond the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. These totals were: at 909 ft elevation, 485 hr; at 932 ft (the AREC NEWA station), 369 hr; and at the 983 ft elevation, 391 hr accumulated wetting hours (ACW). Last week we observed sooty blotch and flyspeck unprotected apple fruit in all areas of the AREC, including the highest elevation. Because early wetting hours this year were more a result of rainfall rather than wetting from dew, expect unusual SBFS pressures in higher elevation orchards, not typically threatened by these diseases. 

Early presence of sooty blotch and flyspeck on Ginger Gold apple in an area not usually affected by these diseases.

For central Virginia, we selected Apr 24 as the petal fall date for accumulation of wetting hours by weather stations at Tyro. As of July 5, a sensor placed at 1465 ft. elevation has now reached 393 wetting hours, while the one at 1165 ft. had accumulated 266 wetting hours, and the one placed at 941 ft elevation has accumulated 466 hr. Also east of the Blue Ridge, the NEWA station at Batesville has passed the 250-hr threshold with 425 ACW while the NEWA station at Gadino Cellars near Washington, VA has recorded 338 ACW using May 1 as the petal fall date. 

We have seen early bitter rot activity at our AREC (pictured below), and there have been several reports of bitter rot and Glomerella leaf spot, as well as SBFS, from central Virginia orchards. 

Early bitter rot infection on unprotected Granny Smith fruit, Virginia Tech AREC, Winchester. 

Early summer disease pressure and continued wet weather

In the past two weeks at  our AREC in Winchester we recorded three more extended wetting events: June 19-20, with 17 hr of wetting at 73° with 0.1 in. rain; June 20-21, with 17 hr of wetting at 71° with 1.44 in. rain; June 21-23, with 35 hr of wetting at 64° with 3.05 in. rain. These wetting events favored early summer disease and rot activity on apples, peach scab, and cherry leaf spot and brown rot on ripening cherries and other stone fruits. 

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 (from May 17 at Winchester). As of 6 AM June 25, all three of our AREC weather stations accumulated more than the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. These totals were: at 909 ft elevation, 391 hr; at 932 ft (the AREC NEWA station), 333 hr; and at the 983 ft elevation, 343 hr accumulated wetting hours (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 25, a sensor placed at 1465 ft. elevation has now reached the 250-hr threshold with 252 wetting hours, while the one at 1165 ft. had accumulated 259 wetting hours, and the one placed at 941 ft elevation has accumulated 466 hr. Also east of the Blue Ridge, the NEWA station at Batesville has passed the 250-hr threshold with 395 ACW while the NEWA station at Gadino Cellars near Washington, VA has recorded 334 ACW using May 1 as the petal fall date. 

We have now confirmed active bitter rot at our AREC (pictured below), and there have been several reports of bitter rot from central Virginia. 

Bitter rot on Honeycrisp apple (Photo by D. Melby)

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. 

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. 

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. 

Summer disease update- bitter rot pressures continue

Bitter rot continues to be the summer disease causing the greatest concern. We are now seeing an unusual amount of fruit drop due to bitter rot in unprotected fruit in our research plots. 

Fruit drop from bitter rot in unprotected Idared fruit

Rainfall over the region has been variable the past month. At our AREC we have not had any single rain events totaling as much as an inch (0.73 inch on Aug 3), but we have recorded rain 15 days with a total of 2.35 inches in August. Two of these rains resulted in extended wetting events at our AREC in Winchester: Aug 7, wet 14 hr at 65° with 0.43 in. of rain and Aug 12, wet 18 hr at 76-66° with 0.23 in. of rain. While the volume of rainfall in individual events has not been excessive, their frequency and brief intensity requires continued regular fungicide coverage to replenish depleted residues as we approach harvest. Our research plots show good bitter rot and general summer disease control where we have maintained good coverage with various fungicide programs. 

For the record, as an indicator of the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew. As of Aug 25, accumulated wetting hours (ACW) since May 4 are now: at 909 ft elevation, 715 hr (with the 250-hr threshold reached Jun 7; sooty blotch first observed Jul 7); at 932 ft (the AREC NEWA station), 486 hr, threshold reached Jul 5; and at the 983 ft elevation, 410 hr ACW, threshold reached Jul 21. These totals are 90 ACW less than last year at the highest elevation and 141 ACW less than last year at the lowest elevation.

As we approach harvest, fruit maturity of earlier varieties such as Ginger Gold and Gala seems to be running about a week early. We are seeing good fruit size, and we are optimistic about good fruit coloring weather, with the 2-week forecast showing most night temperatures with lows in the 50s.  

Increasing bitter rot pressures

Two extended wetting events in the past ten days have brought an increase in summer disease pressure, especially bitter rot at our AREC in Winchester: Jul 22-23, wet 13 hr at 72° with 1.3 in. of rain and Jul 28-29, wet 17 hr at 73-63° with 2.25 in. of rain. Be aware that, as a general guideline, two inches of rain will deplete most protective fungicide residues. 

Bitter rot on Idared apple.

Same fruit as above, cut to show the diagnostic cone-shaped progression of the bitter rot fungus into the fruit.

As an indicator of the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew. As of Aug 1, accumulated wetting hours (ACW) since May 4 are: at 909 ft elevation, 524 hr (with the 250-hr threshold reached Jun 7; sooty blotch first observed Jul 7); at 932 ft (the AREC NEWA station), 363 hr, threshold reached Jul 5; and at the 983 ft elevation, 302 hr ACW, threshold reached Jul 21.  The significance of the 250-hr threshold is that it predicts the presence of the fungi causing SBFS symptoms on unprotected fruit.

Since July 1, rainfall has been scattered, with a total of 3.66 in. for the NEWA station at Gadino Cellars  in Rappahannock County, VA. Augusta County  Barren Ridge, Fishersville rainfall total was less with 1.98 in. in July, but an additional 1.17 in. on Aug 1. July total rainfall was was generally lighter for Albemarle County ranging from 1.89 in. at Batesville, to 0.57 in. at Carter Mt. 

As of Aug 1, accumulation of wetting hours since Apr 30 at Tyro, 941 ft elevation was 512 hr, with the 250-hr threshold reached on June 12. The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) passed the threshold of 250 ACW June 16, and has now recorded 394 wetting hours since May 1. The NEWA station at Fishersville also passed the 250-hr threshold June 16 and now has 390 ACW. Three Albemarle County NEWA stations have also passed the 250-hr threshold, listed with ACW as of Aug 1 and date the was threshold reached: Batesville (367 ACW, July 2); Crozet (309 ACW, July 5); Carter Mt. (292 ACW, July 6).

Summer disease update, July 21.

Overall, conditions remain generally dry, and some good soaking rains would be welcomed for fruit and other crops in the Winchester area. This week we had one extended wetting event at our AREC in Winchester: Jul 17-18, wet 11 hr at 71°  but with only 0.1 in. of rain. As an indicator of earlier wetting conditions, we are now seeing sooty blotch, Brooks fruit spot, and bitter rot on unprotected apple fruits at our AREC . A bright spot in the situation is for ripening peaches, where reduced volume of rainfall should increase sweetness and, hopefully, reduce brown rot pressure.

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 from May 4, 10 days after petal fall. While we have been lacking volume of rainfall, we continue to accumulate wetting hours at lower elevations in the orchard. As of Friday morning July 21, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 439 hr (with the 250-hr threshold reached Jun 7; sooty blotch first observed Jul 7); at 932 ft (the AREC NEWA station), 309 hr, threshold reached Jul 5; and at the 983 ft elevation, 250 hr ACW.  The significance of the 250-hr threshold is that it predicts that the fungi causing SBFS symptoms are now present on unprotected fruit, and that is confirmed by symptoms at our AREC.

For Nelson County in central Virginia, the petal fall date was Apr 20, and accumulation of wetting hours from Apr 30 is recorded by weather stations at different elevations at Tyro. As of July 7, a sensor placed at 1465 ft. elevation had accumulated only 98 wetting hours from Apr 30, while the one placed at 941 ft elevation had accumulated 448 hr, with the 250-hr threshold reached on June 12).

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) passed the threshold of 250 ACW June 16, and has now recorded 360 wetting hours since May 1. A NEWA station at Fishersville also passed the 250-hr threshold June 16 and now has 334 ACW. Three Albemarle County NEWA stations have also passed the 250-hr threshold, listed with ACW as of July 21 and date the was threshold reached : Batesville (313 ACW, July 2); Crozet (277 ACW, July 5); Carter Mt. (259 ACW, July 6).