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. 

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. 

Summer disease update July 8

After a relatively dry month of June in the Winchester area, summer disease activity has increased this past week. There was an extended wetting event at our AREC that will contribute to summer disease pressure: Jul 4-7, wet 38 hr at 70° with 0.88 in. of rain. Some areas east of Winchester and in central Virginia reported more than 2 inches of rain. We are now seeing early sooty blotch symptoms and bitter rot at our AREC in Winchester.

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 July 7, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 380 hr (with the 250-hr threshold reached Jun 7; sooty blotch observed Jul 7); at 932 ft (the AREC NEWA station), 283 hr; and at the 983 ft elevation, 230 hr ACW.  Reaching of the 250 hr threshold 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 96 wetting hours from Apr 30, while the one placed at 941 ft elevation had accumulated 410 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 337 wetting hours since May 1. A NEWA station at Fishersville also passed the 250-hr threshold June 16 and now has 319 ACW. Three Albemarle County NEWA stations have also passed the 250-hr threshold, listed with CWH as of July 7 and date the was threshold reached : Batesville (273 CWH, July 2); Crozet (272 CWH, July 5); Carter Mt. (252 CWH, July 6).

Glomerella leaf spot activity has been reported from central Virginia.

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.

Summer disease update

Summer disease pressure continued this past week with several extended wetting events at relatively warm temperatures and some locally heavy rainfall.

At our AREC we recorded three such extended wetting periods with rainfall: July 11, 9 hr wet at 71-66° with 0.28 in. of rain; July 13, 9 hr wet at 70° with 0.13 in. of rain (but as much as 4 inches with flooding locally in the Woodstock area of Shenandoah County); July 14, 11 hr wet at 70° with 0.34 in. of rain; . These frequent infection periods with rain deplete fungicide residue and continue to favor development of rots such bitter rot and white rot, as well as Alternaria and Glomerella leaf spots.

As of the Thursday morning, July 15, accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 588 hr; at 952 ft elevation, 467 hr; and at the 983 ft elevation 423 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 2.2 wetting hours per foot of elevation drop from 983 to 909 ft!

At Tyro, in Nelson County, total ACW as of Thursday morning, July 15, were: at 941 ft elevation, 531 ACW; at 1165 ft, 299 ACW; and at 1465 ft, 345 (with the 250-hr threshold reached July 5). The 250-hr ACW threshold reached at all sensor elevations at Tyro early last week, and this probably true for all orchards in the central Virginia region.

The recent frequent wetting periods also favor development of brown rot on ripening peaches and other stone fruits.

Continued summer disease pressure

Summer disease pressure continued this past week with a pattern of afternoon or evening showers followed by wetting through the night, all at relatively warm temperatures.

At our AREC we recorded five such extended wetting periods with rainfall: July 2, 10 hr wet at 64-73° with 0.16 in. of rain; July 3-4, 15 hr wet at 72-65° with 0.01 in. of rain; July 6, 9 hr wet at 70° with 0.14 in. of rain; July 6-7, 15 hr wet at 68° with 0.04 in. of rain; July 8-9, 15 hr wet at 68° with 0.05 in. of rain (but more than 1 inch in some local areas). These frequent infection periods all favored bitter rot and Glomerella leaf spot development, as well as other rots, and depleted much fungicide residue for sooty blotch and flyspeck control.

Accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 497 hr; at 952 ft elevation, 390 hr; and at the 983 ft elevation 347 hr ACW. 

At Tyro, in Nelson County, total ACW as of Monday, July 6 were: at 941 ft elevation, 449 ACW; at 1165 ft, 250 ACW; and at 1465 ft, 264 (with the 250-hr threshold reached July 5). Note that the threshold has now been reached at all sensor elevations at Tyro.

The recent frequent wetting periods also favor development of brown rot on ripening peaches.

Summer disease update

Several extended wetting periods at warm temperatures in the past 10 days strongly favored summer disease development: June 14-15, 22 hr wetting at 80-70° with 0.50 in. of rain; June 17-18, 19 hr wetting at 71° with 0.32 in. of rain; June 19-20, 15 hr wetting at 72°with 0.06 in. of rain; June 20-21, 12 hr wetting at 75° with 0.73 in. of rain. Note that all of these were above 70°, indicative of bitter rot and Glomerella leaf spot activity.

For the purpose 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. We are tracking this as we have for the past 21 years using a hygrothermograph located at 952 ft. elevation. The start of wetting hour accumulation was from May 14. At this elevation we reached the 250 total accumulated wetting hour (ACW) action threshold June 13. As of the morning of June 24, ACW at the 952 elevation was 288. We also have electronic recorders at 909 ft and 983 ft elevations. At 909 ft ACW was more rapid with the 250-hr threshold reached June 10 and total ACW at 368 hr.  At 983 ft ACW was slower with the 250-hr threshold not reached until June 21; total ACW at 983 ft was 256 as of June 24 hr. 

For the central Virginia areas, represented by three weather stations at different elevations at Tyro in Nelson County, we started accumulation May 13.  A sensor placed at at 941 ft elevation had already greatly passed the 250-hr ACW threshold June 3 for a total of 335 hr by June 24. By June 24, the ones at higher elevations, 1465 ft and 1165 ft, had not yet reached the 250-hr threshold with only 175 and 183 wetting hours, respectively.

Recent scab and rust infection periods; rust galls still active

We have seen two recent significant scab and rust infection periods: May 16-17 (22 hr wet at 74-71° with 0.77 in. rain) and May 18-19, 16 hr at 72-64° with 0.88 in. of rain.These are important for secondary scab infection where primary infection was not well-controlled earlier and, at temperatures in the 70s and higher 60s, also could signal some early Glomerella leaf spot and bitter rot activity. Cedar-apple rust galls are still actively producing spores.

We have had 22 dry weather powdery mildew infection days since mildew spores were first available Apr 6.

Yesterday we had reports of fire blight symptoms in the region, probably from infection that occurred May 5-7, which Maryblyt predicted to appear May 11-14.

Spring and summer disease update

In the past five days we have had two more apple scab and cedar-apple rust infection periods at our AREC June 4-5: 23 hours wetting at 73-60°, and June 8-9 at 74-66°. Note that cedar rust galls are still actively producing spores.

In addition to developing activity by the usual summer diseases, with the recent warmer wetting periods, be alert for possible early indications of Alternaria leaf blotch on Red Delicious and Glomerella leaf spot on Gala, Golden Delicious and Cripps Pink (Pink Lady) apples. This is also a critical time for protection against Brooks fruit spot.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (CWH) from rainfall or dew, starting 10 days after petal fall. As of this morning, June 8, we had accumulated 80 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

At Tyro, VA we selected May 11 as the start date for accumulation of wetting hours by weather stations at Tyro, VA. As of June 5, a sensor placed in an apple tree at 1165 ft. elevation had accumulated 62 wetting hours from May 11, while one placed at 941 ft elevation had accumulated 128 hr. It is interesting that the station at the highest elevation (1465 ft) registered more wetting hours than the intermediate one, 81 CWH.

Apple and peach disease update

Significant extended wetting periods in the past two weeks occurred July 31- Aug 1 (16 hr with 1.1 in. of rain at 66°) and Aug 3-4 (21 hr with 0.18 in. of rain at 72-60°). As of Aug 5, our accumulated wetting hours since May 13 stood at 471. This is well behind this date last year (729 hr), but comparable to six of the last ten years.

As indicated in our fungicide tests, and from comments coming in from commercial orchards in Frederick County and elsewhere, this weather pattern continues to be favorable for fungal disease development on apples and peaches. Where they were not adequately controlled early, there is scab, mildew and cedar-apple rust; sooty blotch/flyspeck symptoms were readily apparent on non-protected trees in our fungicide test blocks several weeks ago and are now appearing on weaker fungicide treatments.

In the past week I have received several questions and images about leaf spot/leaf blotch symptoms on Golden Delicious. In Frederick County the symptoms appear to be almost entirely related to Golden Delicious necrotic leaf blotch, a physiological problem that can be suppressed by including ziram in the mid-summer cover sprays. But from southern Virginia and North Carolina, I am getting comments and indications that Glomerella leaf spot and the associated bitter rot have been very active on Gala apples as well as on Golden Delicious. We will continue to watch for a repeat of that in Frederick county and surrounding areas.

This year bitter rot, and others, have been associated with fire blight strikes in many areas of Virginia including Frederick County. The shoots and twigs killed by fire blight are quickly colonized by the rot fungi, and fire-blight killed shoots should always be seen as a warning for potential rot problems on apples and pears.

On the positive side, apple fruit size is coming along nicely on well-thinned fruit, and red color is developing early, thanks to the relatively cool nights.

The intermittent rains and wet hours have been near ideal for spread of brown rot spores and incubation on ripening peaches (shown below on Redhaven).



As usual, any type of fruit injury contributes to brown rot problems. This year we are seeing the green June beetle and brown marmorated stink bug injury and fruit cracking as possible factors in brown rot severity.
 

For purposes of predicting 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. As of this morning, June 24, we had accumulated 221 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

Production areas east of the Blue Ridge exceeded the 250-hr threshold for inclusion of a specific SBFS fungicide in the mix as early as two weeks ago. Another indicator of early summer disease activity was appearance of bitter rot on apple samples delivered last week.

In addition to the usual summer diseases, be alert for possible early indications of Alternaria leaf blotch on Red Delicious and Glomerella leaf spot on Gala, Golden Delicious and Cripps Pink (Pink Lady) apples.

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