Wednesday, July 22, 2020

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. 

Sunday, June 21, 2020

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. 

Tuesday, June 9, 2020

Extended wetting events and accumulated wetting hours favor early rot development


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

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

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

Tuesday, June 2, 2020

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.

Tuesday, May 26, 2020

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 infectionThis 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. 

Tuesday, May 19, 2020

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.

Tuesday, May 12, 2020

Secondary scab infection May 5-6; fire blight infection conditions on late bloom May 15-18.

At Winchester, most apple varieties are well beyond petal fall, but late bloom susceptible to fire blight persists on some late varieties and some recently planted trees

At the AREC last week an apple scab infection period occurred May 5-6: 17 hr wet at 47° with 0.18 in. rain. Similar conditions also extended south to Staunton and east of the Blue Ridge from Loudoun County to the Charlottesville area, where infection conditions resulted from a combined wetting period. At Winchester, cedar-apple rust galls and quince rust cankers remain active after this wetting event.

Apple powdery mildew infection occurs on days without rainfall above 53°, and we have had 14 days favorable for infection since spores were available on Mar 29. Below is an example of primary and secondary powdery mildew on Idared apple.


A secondary powdery mildew lesion (bottom left) next to a primary mildew shoot on Idared apple. 

The Winchester area will likely see its first fire blight infection conditions wherever susceptible bloom remains this weekend, May 16-18. Similar conditions exist for all other major fruit producing areas of Virginia, but with some starting on May 15. Blossom infection has already been reported on apples east of the Blue Ridge south of Charlottesville and in southwest Virginia, and on pears in Clarke County from infection that occurred six weeks ago. Below is an example of late bloom that was observed on Goldrush apple in Nelson County last week.


Late bloom and set fruit on Goldrush apple in Nelson County May 7, 2020.
Just to add a footnote about the unusually cool conditions through April and into mid-May that allowed the Winchester area to escape fire blight infection from Mar 30 until the very latest of bloom: The daily mean high temperature for April this year was 60.0° and, since 1928 only three years had a cooler mean daily high temperature, 1935, 1961, and 1966!  Meanwhile, 17 years had a mean April high greater than 70°

Tuesday, May 5, 2020

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


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

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

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

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

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


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

Tuesday, April 28, 2020

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


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

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

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

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

Tuesday, April 21, 2020

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


At Winchester apple trees are mostly at mid-bloom. 

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

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

This will be updated again Apr 28.

Tuesday, April 14, 2020

Apple scab and rust infection April 12-13; fire blight pressure low to moderate through April 19.


At Winchester apple trees are mostly at mid-bloom, with later cultivars coming into bloom

At the AREC we received an apple scab, quince rust and cedar-apple rust infection period Apr 12-13 with 15 hr wet at 57° with 0.74 in. rain. Earlier last week we also had a possible combined scab/rust infection period Apr 7-8 with 9 hr wetting at 57° with 0.94 in. rain.  More than 95% of the scab ascospores are now mature in the Winchester area. At Winchester, we have had 10 days favorable for apple powdery mildew infection since spores were available.

Most of the commercial fruit production areas in Virginia had similar scab and rust infection conditions Apr 12-13, but with more rainfall east of the Blue Ridge and southward. Rainfall ranged from 1.5 inches at Sperryville and 2.3 inches at Manassas to 3.36 inches at Lynchburg. Such volumes of rainfall deplete fungicide protection, calling for fungicides with after-infection control for scab and rusts, as well as something for protection against powdery mildew in mildew-susceptible cultivars..

FIRE BLIGHT: With most apples in bloom, the current fire blight threat remains moderate to low in the Winchester area. 


Graphic from Cougarblight, April 14, 2020. Click to enlarge.

Above is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 3/30/20. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is moderate or low through Apr 19. The Roanoke area and areas east of the Blue Ridge south of Charlottesville had possible infection Apr 7-9 (graphics not shown), and after high risk Apr 13, are now also showing moderate to low infection potential through Apr 19.

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

Monday, April 6, 2020

This week's fire blight outlook for Winchester and beyond

NOTE: This year for fire blight risk assessment, I will post a graphic from the Cougarblight model as shown on our NEWA site. I will be using the same weather data from our NEWA station to make a comparison to Maryblyt 7 as in previous years, but not posting the MaryBlyt graphic. We thank Dr. Mizuho Nita for hosting the Maryblyt 7.1 download site at: http://grapepathology.org/maryblyt 

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

Graphic from Cougarblight, April 6, 2020. Click to enlarge.
FIRE BLIGHT: Above is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 3/30/20. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is low or caution for this week Apr 7-11. The Roanoke area and areas east of the Blue Ridge south of Charlottesville have a potential for infection Apr 7-9 (graphics not shown). Setting the first bloom date to 3/25/20 instead of 3/30/20 did not make any difference in prediction of infection for this week. However, Roanoke and areas south of Charlottesville could have had earlier infection (March 27-31) if the first bloom date had been as early as March 20.

Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection, which occurs with wetting. The fire blight outlook will be updated Apr 13.

Monday, March 30, 2020

Apple scab infection March 27-28; powdery mildew infection Mar 29-30

At Winchester we are seeing mostly pink stage, with a few early blossoms open on Idared and Pink Lady apples. At the AREC we received our first definite apple scab infection period Mar 27-28 with 15 hr wet at 53° with 0.57 in. rain. More than half of the scab ascospores are now mature in the Winchester area. Only a few cedar-apple rust spores were discharged during the recent wetting, but spore horns are now fully mature. Apple powdery mildew spores are available, and infection could have occurred on Mar 29 and 30.

As shown below, a few early apple and crabapple blossoms were open Mar 30. However, with cool temperatures predicted most of the next two weeks, the current fire blight threat is minimal in the Winchester area.
Early bloom on Idared apple, March 30, 2020. Winchester, VA.


Sunday, March 22, 2020

Early season apple disease activity

Due to other pressing commitments this year, some of my updates and bud development stages may be delayed. Every orchardist should be aware of ongoing developments in their own orchard and protect or react accordingly.  The updates for the Winchester area are based on the AREC's NEWA weather station as they have been since 2017. This resource and other NEWA stations in Virginia are available publicly, and all growers and advisers should be using them in their disease management decisions. 
Tight cluster stage on Red Delicious at Virginia Tech AREC, Winchester. Note the small mummified blossom next to the developing flower cluster. These and dead twigs are a common source for spores of fruit rot and frogeye leaf spot fungi.

Apple scab outlook: At Winchester on Sunday March 22, we are seeing tight cluster stage on Red Delicious and other advanced cultivars. Because of potential for fruit russet, this stage is too late for application of copper sprays to fresh market fruit, and another protectant fungicide should be used ahead of infection. With green tip set at March 7, the apple scab program on our AREC NEWA station indicates that 17% of the scab ascospores have matured, and many would be ready for a potential infection period with combined wetting over the next several days or later in the week. This is a high level of ascospore maturity for the first infection period of the year and could result in heavy primary infection on the large susceptible target. 

Where there is concern that scab infection may have occurred without any fungicide protection, it would be prudent to mix Vangard (cyprodinil) with a protectant to improve post-infection control. Dodine (Syllit) is another early season option where scab may be the only apple disease of concern up to pink stage. Do not use Syllit after pink stage. 

Expect powdery mildew and rust activity soon in orchards prone to these disease problems. 

For the Roanoke area and areas east of the Blue Ridge, please check NEWA stations in your region, adjust your green tip stage setting and hit 'calculate' to predict scab status in your area. Generally, these areas have higher percent ascospore maturity and had their first infection period last week if green tip was present by March 1. The Gadino Cellars NEWA station in Rappahannock County indicates that scab infection could have occurred as early as March 2-3 if green tip was present by March 1

Wednesday, August 14, 2019

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.

Tuesday, July 16, 2019

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). 

Saturday, July 6, 2019

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.

Wednesday, June 12, 2019

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.