Bitter rot; sooty blotch, flyspeck threshold and activity

Conditions have been dry at Winchester, with only three extended wetting events at Winchester in the past month:  June 27-28: 9 hr of wetting at 72° with 0.17 in. rain, July 10-11: 6 hr of wetting at 71° with 0.07 in. rain, and July 21-22: more than 10 hr of wetting at 72° with 0.28 in. rain. In spite of the rain received July 21, the Winchester area is still experiencing drought, with July rainfall total at Winchester AREC only 0.49 inches.

Bitter rot (shown below) was observed in a organic production block July 21. This indicates that, although weather has been dry the past month, there was ample opportunity earlier for bitter rot infection which is now evident. 

Bitter rot in Honey Crisp apples July 21, 2020. Likely inoculum source was a large overwintering fruit mummy (upper left).

Bitter rot in Honey Crisp apple July 21, 2020. Likely inoculum source was small, current season, fruit mummies (upper left).

Other areas of Virginia have received variable amounts of rainfall in the past month. Some areas have been dry like Winchester, while others have received adequate moisture. Few have had excessive rainfall, but all could have bitter rot conditions as favorable as those in Winchester.

To predict the development of the sooty blotch and flyspeck (SBFS) fungal complex, 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. After several weeks delay, Winchester and Sperryville have now exceeded the 250-hr threshold. Here is a listing of selected petal fall dates and total wetting hour accumulation (ACW) for selected locations as of the night of July 21: Winchester, May 5, 271 ACW; Staunton, May 5, 591 ACW; Roanoke, Apr 18, 423 ACW; Floyd, Apr 28, 342 ACW; Manassas, Apr 28, 461 ACW; Sperryville, Apr 28, 272 ACW; Crozet, Apr 18, 332 ACW; Carter Mountain, Apr 18, 473 ACW; Red Hill, Apr 18, 375 ACW; Lynchburg, Apr 13, 488 ACW; Rustburg, Apr 13, 361 ACW; Danville, Apr 13, 667 ACW. 

Extended wetting periods and volumes of rainfall expected to increase sooty blotch/flyspeck and rot pressure

Three extended wetting events at Winchester in the past week favored secondary apple scab  and summer disease development.  These occurred June 10-11: 10 hr of wetting at 73° with 0.23 in. rain, June 17-18: 14 hr of wetting at 65° with 0.69 in. rain and June 21: 16 hr of wetting at 65° with 0.01 in. rain. Cedar-apple rust infection on leaves over most of the length of unprotected shoots (shown below) indicates that infection occurred well into June this year, but galls have now been depleted of inoculum at Winchester AREC.

Cedar-apple rust on York Imperial apple shoot June 20, 2020.
Lesions on all but the youngest leaves show that infection occurred well into June.

Apple powdery mildew infection occurs on days without rainfall above 53°, and in the Winchester area we have had 38 days favorable for infection since spores were available on Mar 29.

Other areas of Virginia also received significant wetting events in the past two weeks, June 10-11, and especially June 14-19. Some of these were extremely long wetting periods with heavier rainfall than Winchester: Staunton June 16-19, 51 hr with 1.88 in. of rain; Roanoke three wetting periods June 14-18, totaling 65 hr and 5.75 in. rain; Batesville June 16-19, 44 hr with 1.31 in. rain; Carter Mt., June 15-18, 64 hr with 0.91 in. rain; Red Hill, three wetting periods June 13-19, totaling 54 hr and 0.9 in. rain; Lynchburg, two periods June 15-19, total 76 hr and 3.79 in. rain; Rustburg, June 14-19, two periods totaling 79 hr and 3.81 in. rain; Danville, two periods, total 67 hr and 1.8 in. rain. These long wetting periods and volumes of rainfall should be expected to increase pressure from sooty blotch and flyspeck and various fungal rot diseases.

To predict the development of the sooty blotch and flyspeck (SBFS) fungal complex, 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. All of the monitored areas except Winchester and Sperryville have now exceeded the 250-hr threshold, and Winchester and Sperryville will likely pass the threshold in the next 7-10 days. Here is a listing of selected petal fall date and total wetting hour accumulation (ACW) for selected locations as of June 21: Winchester, May 5, 187 ACW; Staunton, May 5, 324 ACW; Roanoke, Apr 18, 316 ACW; Floyd, Apr 28, 291 ACW; Manassas, Apr 28, 257 ACW; Sperryville, Apr 28, 199 ACW; Batesville, Apr 18, 316 ACW; Crozet, Apr 18, 276 ACW; Carter Mountain, Apr 18, 435 ACW; Red Hill, Apr 18, 291 ACW; Lynchburg, Apr 13, 366 ACW; Rustburg, Apr 13, 361 ACW; Danville, Apr 13, 450 ACW. 

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). 

Variable summer disease pressures

Summer disease pressures the past month have been generally lighter at Winchester than in other parts of Virginia. 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 hours accumulated quite rapidly in May, but more slowly in late June and early July; however, rains the past two days have brought the total ACW (234 hrs) approaching the 250 hr threshold with more rain expected through the weekend. ACW is similar to Winchester at Roanoke (239 hr).

Other areas of Virginia generally had more rainfall than Winchester and more wetting hours in June. Examples, with ACW totals, are: Staunton (377 hr); Rappahannock County (Gadino Cellars) 319; Red Hill (733 hr); Lynchburg (480 hr); Floyd (331 hr); Danville (548 hr). 

At our AREC in Winchester we recorded only three extended wetting events since the posts early last month: Jun 13 (10 hr wet at 59° with 0.19 in. rain; Jun 24 (9 hr wet at 74° with 0.54 in. rain); and Jul 4-5 (16 hr wet at 70° with 0.74 in. rain). Other local areas experienced thunderstorms which resulted in more total rainfall and, especially where those occurred in the evening, more ACW.

Summer disease activity

At our AREC in Winchester we recorded an extended wetting event: Jun 9-10, with 30 hr of wetting at 63° with 0.62 in. rain. This wetting favored development of secondary apple scab, early summer disease activity on apples, peach scab, cherry leaf spot and brown rot on ripening cherries. 

Other areas of Virginia generally had more rainfall and longer wetting in the past week with these examples: Rappahannock County (Gadino Cellars) 30 hr wet at 63° with 1.84 in. rain; Red Hill (Jun 7-11, 67 hr wet at 62-70° with 3.5 in. rain); Lynchburg (Jun 7-11, 53 hr wet at 63° with 2.35 in. rain); Roanoke (Jun 6-10, 63 hr wet at 68° with 4.39 in. rain); Floyd (Jun 6-11, 90 hr wet at 63° with 3.25 in. rain); Danville (Jun 6-9, 55 hr wet at 70° with 2.47 in. rain). Heavy amounts of rainfall and lengthy wetting periods at warm temperatures are favorable for Glomerella leaf spot and bitter rot and other fruit rots as well as sooty blotch and flyspeck.

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 Jun 11, accumulated 147 wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex at our AREC NEWA station, 932 ft elevation. (Last week I had noted that at a lower elevation, 909 ft, we had already accumulated 331 hr ACW, but 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). 

Most other areas of Virginia have accumulated more wetting hours than Winchester, based on approximate petal fall dates and increased length of wetting in these areas: Rappahannock County (Gadino Cellars) 199 hr; Red Hill 472 hr; Lynchburg, 319 hr; Roanoke, 172 hr; Floyd 220 hr; Danville, 364 hr. Note that the values shown in bold font have passed the 250 wetting hour threshold. This means that the SBFS fungi are now present on unprotected fruit, and would develop symptoms if samples were taken and incubated under moist/humid conditions. Specific protection against SBFS and the rots is recommended at this time.

Peach brown rot: The 3-week period leading up to harvest for individual peach varieties and other stone fruits is a critical time for protection from brown rot. Weather conditions, especially rainfall, will affect how much rot appears on varieties as they ripen. During this period, step up the program to include fungicides specifically active against brown rot. Include Captan with those classes of chemistry that are at risk for development of resistance and rotate chemical classes in the final applications. Application interval should be about 3 weeks and 1 week to harvest for ‘normal’ conditions, but might need to be shortened to offset frequent, heavy rainfall.

Continued heavy summer disease pressures

This past week marked a return to the heavy disease pressures noted from mid-May through early July. At our AREC in Winchester we recorded three extended wetting events: July 24, with 14 hr of wetting at 72° with 0.67 in. rain; July 24-25, with 12 hr of wetting at 70° with 0.44 in. rain and July 25-26, with 17 hr of wetting at 69° with 1.17 in. rain. Rainfall volumes varied considerably over the region, but with similar temperatures and length of wetting. These wetting events favored all summer diseases and rot activity on apples, and brown rot on ripening peaches 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 8 AM July 27, AREC weather stations at three elevations had greatly exceeded the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. These totals were: at 909 ft elevation, 678 hr; at 932 ft (the AREC NEWA station), 459 hr; and at the 983 ft elevation, 528 hr accumulated wetting hours (ACW). Sooty blotch and flyspeck are common on unprotected apple fruit in all areas of the AREC, including the higher elevations. 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. 

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 1165 ft. has accumulated 322 wetting hours while one placed at 941 ft elevation has accumulated 733 hr. 

We see continued bitter rot activity at our AREC and there have been several reports of bitter rot and Glomerella leaf spot, as well as SBFS, from central Virginia orchards. 

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. 

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.  

Extended wetting event June 16-17, and accumulated wetting hours

The past 10 days there was one extended wetting at our AREC event that could contribute to summer disease pressures in the coming weeks: Jun 16-17, wet 20 hr at 70° with 0.62 in. rain. 

For purposes of predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. This year our petal fall date at Winchester was Apr 24, so the start of wetting hour accumulation was from May 4. As of Friday morning June 23, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 316 hr (with the 250-hr threshold reached Jun 7); at 932 ft (the AREC NEWA station), 226 hr; and at the 983 ft elevation, 183 hr ACW.  Reaching of the 250 hr threshold predicts that the fungi causing SBFS symptoms are now present on unprotected fruit and that symptoms on such fruit should appear in about 2 weeks.

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. Wetting hour accumulation in central Virginia was slow last week. As of June 23, a sensor placed at 1465 ft. elevation had accumulated only 90 wetting hours from Apr 30, while the one placed at 941 ft elevation had accumulated 341 hr- just over the 250-hr threshold).

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) passed the threshold of 250 ACW last week, and has now recorded 286 wetting hours since May 1. A NEWA station at Fishersville has also passed the 250-hr threshold with 294 ACW.

Early 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 our petal fall date at Winchester was Apr 24, so the start of wetting hour accumulation was from May 4. As of Monday morning June 5, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 241 hr; at 932 ft (the AREC NEWA station), 180 hr; and at the 983 ft elevation, 143 hr ACW. In the past week most of the wetting hour accumulation was from dew and occurred more at lower elevations in the orchard. Note that at the lowest elevation, the ACW of 241 hr will probably reach the threshold level of 250 ACW this week.

For Nelson County in central Virginia the petal fall date was Apr 20, and accumulation of wetting hours from Apr 30 is recorded by three weather stations at different elevations at Tyro. Wetting hour accumulation in central Virginia was slow last week. As of June 5, a sensor placed at 1465 ft. elevation had accumulated only 76 wetting hours from Apr 30, while the one at 1165 ft. had accumulated 151 wetting hours, and the one placed at 941 ft elevation had accumulated 199 hr.

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) will probably also reach the threshold level of 250 ACW this week, having recorded 238 wetting hours since May 1.

We have had several reports of other early summer disease activity: bitter rot mummies forming on fire-blighted shoots and early Glomerella leaf spot symptoms in central Virginia and Alternaria leaf blotch on Red Delicious in Rockingham County.

Disease Update; Accumulated wetting hours and extended wetting events

Early this week we recorded another extended wetting event at our AREC: May 28-29, wet 12 hr at 63° with 0.04 in. rain. 

For purposes of predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. This year we chose Apr 24 as our petal fall date for Winchester, so the start of wetting hour accumulation was from May 4. As of Monday morning May 29, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 204 hr; at 932 ft (the AREC NEWA station), 167 hr; and at the 983 ft elevation, 139 hr ACW. In the past week some wetting hour accumulation occurred from both rainfall and dew. 

For central Virginia, we have selected Apr 20 as the petal fall date, and accumulation of wetting hours from Apr 30 is recorded by three weather stations at different elevations at Tyro. As of May 29, a sensor placed at 1465 ft. elevation had accumulated only 75 wetting hours from Apr 30, while the one at 1165 ft. had accumulated 147 wetting hours, and the one placed at 941 ft elevation had accumulated 187 hr.

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) has recorded 206 wetting hours since May 1.

More of the same...

We have had several more extended wetting periods this week, favorable for both scab and cedar-apple rust and early summer disease development: May 23-24, wet 11 hr at 54° with 0.48 in. rain; May 24-25, wet 15 hr at 55° with 0.96 in. rain; . May 25-26 wet more than 9 hr at 56° with 0.56 in. rain.

Apple scab pressure has been significant this year, with five infection periods Mar 27- Apr 7 and enough rainfall to cause weathering of protectant fungicides during that time. Lesions from those infection periods were present to cause secondary infection Apr 22-26 and during later infection periods May 4-6, May 11-13, May 21-22, and the recent ones this week. Combinations of fungicides with protective action and after-infection activity for scab are suggested for control during repeated conditions with 1-2 inches of rainfall followed by extended wetting that favors additional infection.

Cedar-apple rust: Rusts have been active for 8 weeks and cedar rust galls were still active May 25-26. Cedar-apple rust lesions and some quince rust lesions are present from the Apr 24-26 and May 4-6 infection periods and more foliar infection is appearing from the more recent ones. Considering continued cedar gall activity and infection conditions this week, it would still be prudent to include an SI fungicide for after-infection rust control in the next application if there is any doubt about lack of protective residue. The recent wetting will add to the accumulated wetting hour totals for development of sooty blotch and flyspeck which will be updated early next week.

Stone fruits: Continue to protect peaches against peach scab which is also favored by the above conditions described for apple scab. Also, protect ripening cherries against brown rot and Alternaria rot which are favored by these wet conditions during the pre-ripening period.