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.

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. 

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. 

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. 

Rapid bud development; powdery mildew, scab and rust activity

The past two days we have seen rapid apple bud development in the Winchester area. Friday morning, Apr. 13, we saw heavy powdery mildew sporulation on Idared buds at tight cluster stage. Powdery mildew infects on dry days at temperatures above 53°F, so there were several infection days this week.

Powdery mildew on Idared, Friday morning, Apr. 13, 2018.

By Friday evening, many buds were showing color at the pre-pink stage. With warm temperatures over the weekend, expect open bloom by early next week.

Pre-pink stage of Idared buds Friday evening, Apr. 13, 2018

There is a forecast for thunderstorms and rain with temperatures in the 50s Sunday and into Monday, Apr 15-16, and that would bring a scab infection period as well as our first cedar-apple and quince rust infection period in the Winchester area. 

Cedar-apple rust gall with developing spore horns Apr. 11, 2018

 Generally, the forecast is similar for the areas south to beyond Roanoke and east of the Blue Ridge, with a trend toward earlier and a shorter wetting period, but with warmer temperatures to the south. In short, scab, the rusts, and powdery mildew are now active, and there is a potential for fire blight infection in more advanced areas with open bloom.

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

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).

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.

Apple summer disease and peach brown rot alert

Recent wetting events totaling more than 3 inches of rain would have depleted any and all fungicide residues available to protect against apple fruit rots and sooty blotch/flyspeck and brown rot on ripening peaches. For the record, July 28-29 we had 17 hr wet at 71-67°, with 1.89 in. rain, and for July 30-31 it was 17 hr wet at 72-67° with 1.43 in. rain.

Continued summer disease pressures

Summer disease pressures have advanced at a relatively steady pace over the past two weeks, with several extended wetting periods and continued accumulation of wetting hours.  As of Monday, July 18, we were more than 2 weeks past the 250-hr accumulated wetting hour threshold (ACW) for all of the wetness sensors at our AREC, Winchester and for Tyro, VA. Altough the volume of rainfall has not been excessive, shower activity has favored spread of fungal spores for fruit rots such as bitter rot on apples and brown rot on peaches and other stone fruits.

Wetting hour accumulation (ACW) at Winchester: at 909 ft elevation, 555 hr (with the 250-hr threshold reached June 5); at 952 ft elevation, 419 hr (near the threshold); and at the 983 ft elevation, 341 hr ACW. At Tyro, VA  as of July 18, a sensor placed at the 941 ft elevation had accumulated 529 hr (with the 250-hr threshold reached June 6); the one at 1165 ft. elevation had accumulated 309 wetting hours, and the one 1465 ft. elevation had accumulated 341 . 

At Winchester in the past two weeks we had three significant extended wetting events favorable for SBFS and fruit rot development: July 4-5: 20 hr at 71-67°, with 0.74 in. rain, July 12-13: 13 hr at 77-66° with 0.04 in. rain, and July 16-17: 15 hr at 77-65° with 0.34 in. rain. Bitter rot was observed on apple fruit at Winchester as early as June 22, and all of these recent wetting periods were at temperatures favorable for bitter rot. Specific treatment against the SBFS fungal complex and rot diseases is advised.

We have installed a new, publicly accessible weather station at our AREC in Winchester. The station, which updates hourly, is located near the labooratory building at an elevation of 933 feet. This station is part of the NEWA system, so to access it one can either click on the  NEWA weather station locator map, or go directly to: 
       http://newa.cornell.edu/index.php?page=weather-station-page&WeatherStation=va_win

A caution about the station is that because it was installed after the beginning of this year's wetting hour accumulation period (May 14), it will not be up to date for predictions in the sooty blotch/flyspeck model.

Increasing summer disease and brown rot pressures

Summer disease pressure increased in the past week, with two extended wetting events at our AREC: Aug 6-7, 16 hr wet at 68-65° with 0.11 in. of rain and Aug 9-10, 16 hr wet at 74-72° with 0.52 in. of rain. (Another extended wetting event is in progress at the time of this post).

As of the Monday morning, Aug 10, total accumulated wetting hours (ACW) at the AREC were: at 909 ft elevation, 796 hr; at 952 ft elevation, 567 hr; and at the 983 ft elevation, 518 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 3.8 wetting hours per foot of elevation drop from 983 to 909 ft.

At Tyro, in Nelson County, total ACW as of Monday morning, Aug 10, were: at 941 ft elevation, 670 ACW; at 1165 ft, 368 ACW; and at 1465 ft, 409 ACW. 

The recent wetting events will again increase brown rot pressure on ripening peaches, as well as sooty blotch, flyspeck and rots on early ripening apples.

Summer disease update

Yesterday we received several rains totaling 3.6 inches at a mean temperature of 70°. This volume of rain would remove most of any protective fungicide residue applied before the rains, indicating need for tightening spray intervals for summer disease control on apples and for reliable control of brown rot on peaches and other stone fruits. Scab symptoms are very evident on non-protected peaches.

Wetting hours accumulated last week (38) brought our total to 383 hours. This is less than for this time last year, but ahead of 2010 and 2011.

Extended wetting at mild temperatures- a preview of summer diseases?

We had an extended wetting period at our AREC June 6-8: 40 hours wetting with 1.1 inches of rain at 63°. Today's rain has added another 0.4 in. of rain and it may not be finished yet. Those rains combined to remove much of any fungicide residue applied earlier last week, leaving the trees possibly vulnerable to secondary apple scab and Brooks spot infection; also think of these wetting events as initiating early activity by the Alternaria and Glomerella leaf spot fungi. The rains may cause cracking of ripening sweet cherries and will increase the potential for fruit rots:  http://treefruitdisease.blogspot.com/2010/06/cherry-rots.html

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours, starting 10 days after petal fall. As of this morning, June 10, we had accumulated 145 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. Because of an earlier petal fall date and more wetting, some areas east of the Blue Ridge may now be approaching the 250-hr threshold for inclusion of a specific SBFS fungicide in the mix.
 
As of today, June 10, we have had 40 dry weather apple powdery mildew days since spores were first released Apr 11, ranking this year among the higher mildew pressure years. The recent rains will promote continued tree growth and susceptibility to mildew infection. Maintain mildew suppression on susceptible cultivars until shoot growth ceases to prevent the bud infection which leads to overwintering and a recurrent problem next year.

I have received several reports of fire blight showing up, likely from infection that occurred at late bloom: 
http://treefruitdisease.blogspot.com/2013/05/fire-blight-threat-to-late-bloom.html

Extended wetting August 5-6.

Extended wetting occurred Aug 5-6 with 13 hours wet at 73° and 0.41 in. rain. Accumulated wetting hour total from rainfall or dew since Apr 18 is now at 729 hours, 277 hours ahead the total for this time last year. This is the third highest wetting hour total for this time of the year since 1994. At our AREC, total rainfall for last week was 2.86 inches.

Watch for increased disease pressure from sooty blotch and flyspeck, fruit rots and Alternaria leaf blotch, the fungal disease that causes defoliation and poor fruit quality of Red Delicious apples.

Extended wetting periods and summer disease development

Three extended wetting periods have added to summer disease pressure locally in the past week. At our AREC we recorded: 29-30 June, 10 hr wet at 66° with 0.44 in. rain; 2 July, 8 hr wet at 70° with 0.2 in. rain; 4-5 July, 8 hr wet at 72° with 0.11 in. rain. Some areas to the north in Frederick County probably received more rain than we did. All of these storms had strong winds that could have resulted in some fruit injury, increasing the potential for fruit rots. the accumulated wetting hour total from rainfall or dew since Apr 18 now stands at 470 hours, more than 120 ahead of this date last year.


These warm wetting periods will also increase the threat of brown rot on ripening stone fruits.

Extended wetting periods May 27-30 and accumulated wetting hours

We had extended wetting May 27-28: 11 hours with 65° and 0.33 in. rain. Last night's extended wetting, May 29-30, was 10 hours at 71° and 0.12 in. rain. These wetting periods favored secondary scab and all summer diseases on apples and brown rot on ripening cherries and other stone fruits.


On May 25 we passed the 250-wetting hour threshold for specific treatment against the sooty blotch/flyspeck fungal complex. Accumulated wetting hour total from rainfall or dew since Apr 18 is now at 285 hours. This is four weeks ahead of last year and the second earliest week for reaching this predictive threshold since we began recording this in 1994. In seven of these 19 years we reached this threshold one week later.

Extended wetting May 24-25

Last night's extended wetting came to 15 hours with 60-70° temperatures and 0.06 in. rain. This wetting favored scab and all summer diseases on apples and brown rot on ripening cherries and other stone fruits.

Last week we accumulated an additional 16 wetting hours which brings us to a total of 360 hours, 110 hr past the 250-hour action threshold for development of sooty blotch and flyspeck on unprotected fruit. Total rainfall for the week was 0.22 inches.

Below is a picture of brown rot on Klondike White peach, taken last week. The dieback of shoots indicates high susceptibility of this cultivar, similar to what we have occasionally seen on Redgold nectarine. Klondike White is also very susceptible to bacterial spot. In this case the brown rot infection was probably initiated by hail injury followed by cracking of the fruit with increased growth. At our AREC, brown rot pressure has not been unusually high yet this year but this does not bode well for this local situation, and removal of early infected fruit might be beneficial to prevent spread to later ripening cultivars.