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.

Sunday, June 2, 2019

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. 

Wednesday, May 15, 2019

Heavy scab infection period May 10-12.

We recorded another heavy combined apple scab infection period at Winchester over this past weekend: May 10-13 (47 combined hr wet at 53° with 1.44 inches of rain). Scab lesions have been observed on unprotected trees in the Winchester area. A follow-up fungicide application with after-infection scab activity is suggested. Cedar-apple rust gall inoculum is now mostly depleted.

Also, we have had 20 days favorable for powdery mildew infection since spores were available at Winchester Apr 6. 

Monday, May 6, 2019

Heavy scab and rust infection, May 3-6

We recorded two heavy apple scab and rust infection periods at Winchester over the weekend: May 3-4 (19 hr wet at 64° with 0.4 inches of rain) and May 4-5 (more than 21 hr wet at 62° with 2.18 inches of rain). The last wetting period, with heavy rainfall, is still in progress. This amount of rainfall depleted any fungicide residue applied last week, resulting in potentially heavy rust and scab infection to foliage and fruit. A follow-up fungicide application with after-infection activity is suggested.

Also, we have had 18 days favorable for powdery mildew infection since spores were available at Winchester Apr 6. The fire blight outlook for Winchester remains much as indicated in the post on May 2: the risk of infection remains high wherever there is late bloom present.

Thursday, May 2, 2019

Fire blight outlook into next week

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. Fruit producers in other areas are encouraged to consult their state extension specialists for information similar to that provided here.
Graphic from Maryblyt 7, May 1, 2019. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. We have moved through bloom in a timely fashion in the Winchester area, but many apple blocks still have some susceptible bloom. The temperature and rainfall data are current through Wednesday evening, May 1. Predicted weather conditions are shown for May 2-6. 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 Apr 19 and 25, and was possible with wetting Apr 18, 23 and 24, and will again be possible with wetting May 2-4. The temperature is marginally close for infection May 5. The extended outlook May 6 through May 10 (not shown) indicates infection is possible wherever there is bloom and wetting through May 10.
Streptomycin application is recommended for tomorrow, May 2, to protect any late bloom into the weekend. Also, remember to protect any young and recently planted trees that have flowers. Predicted temperatures into next week (not shown) indicate that infection will remain possible wherever there is late bloom and wetting every day next week. Note that "wetting" can occur with maintenance and thinning applications, so streptomycin should be included in such applications where there is late bloom. 
The BBS column tracks the appearance of blossom blight symptoms from infection that occurred Apr 19, which is now predicted for May 3. The CBS column is tracking canker blight symptom appearance and predicts canker margin symptoms (CMS, expansion of overwintered cankers) is predicted May 1. Further tracking in the CBS column will predict canker blight symptoms when that value reaches 100.

Below is the graphic from the Cougarblight model as shown on our NEWA site. with “Fire blight occurred in your neighborhood last year” selected as the orchard blight history option and first blossom open date as 4/13/2019. Cougarblight shows color-coded risk assessments as “Cougarblight 4-Day DH” and infection potential EIP value. This risk is "extreme" for May 2-6, with infection possible if wetting occurs May 2-4. The average temperature of 60 F is lacking for May 5.
Graphic from the NEWA/Cougarblight model, May 1, 2019. Click to enlarge.

Fire blight risks can change quickly with warmer than predicted temperatures and wetting; in high-risk situations, a streptomycin application is more effective when applied ahead of predicted infection. Unless unexpected weather conditions arise, this will be the last fire blight update for this season.

Monday, April 29, 2019

Fire blight outlook Apr 29-May 4; secondary scab infection Apr 27-28.

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. Fruit producers in other areas are encouraged to consult their state extension specialists for information similar to that provided here.
Graphic from Maryblyt 7, April 29, 2019. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most apple trees still have susceptible bloom in the Winchester area. The temperature and rainfall data are current through Sunday evening, April 28. Predicted weather conditions are shown for April 29-May 4. 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 Apr 19 and 25, and would be possible with wetting Apr 18, 23 and 24, and will again be possible with wetting May 1-4. 
Streptomycin application is recommended for tomorrow, Apr 30 or Wednesday, May 1 to protect late bloom into the weekend. Also, remember to protect any young and recently planted trees that have flowers. Predicted temperatures into next week (not shown) indicate that infection will remain possible wherever there is late bloom and wetting every day next week. Note that "wetting" can occur with maintenance and thinning applications, so streptomycin should be included in such applications while late bloom is present. The BBS column tracks the appearance of blossom blight symptoms from infection that occurred Apr 19, which is predicted for May 2. The CBS column is tracking canker blight symptom appearance and predicts canker margin symptoms (CMS, expansion of overwintered cankers) is predicted Apr 30.

Below is the graphic from the Cougarblight model as shown on our NEWA site. with “Fire blight occurred in your neighborhood last year” selected as the orchard blight history option and first blossom open date as 4/13/2019. Cougarblight shows color-coded risk assessments as “Cougarblight 4-Day DH” and infection potential EIP value. This risk is "extreme" for May 1-4 with infection possible if wetting occurs. 
Graphic from the NEWA/Cougarblight model, April 29, 2019. Click to enlarge.
Note that real fire blight risks can change quickly with warmer than predicted temperatures and wetting and, in high-risk situations, a streptomycin application is more effective when applied ahead of predicted infection.
We recorded a secondary apple scab infection period at Winchester Apr 27-28: 13 hr wet at 50° with 0.16 inches of rain. This would have been a secondary infection period where scab was not well controlled during the Apr 5-6 infection, resulting in scab lesions with spores now available for secondary infection. 

Saturday, April 27, 2019

Scab and rust infection Apr 25-26

We recorded a apple scab and rust infection period at Winchester Apr 25-26: 14 hr wet at 57° with 0.13 inches of rain. This was also an infection period in central Virginia and could have been a secondary infection period where scab was not well controlled during the Apr 5-6 infection, resulting in scab lesions with spores now available for secondary infection. Cedar-apple rust lesions are now visible from the infection period Apr 7-8.

Also, we have had 14 days favorable for powdery mildew infection since mildew spores were available at Winchester Apr 6.

Wednesday, April 24, 2019

Fire blight infection possible April 25

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 Maryblyt 7, April 24, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Apple trees are near full bloom in the Winchester area. The temperature and rainfall data are current through Tuesday night, April 23. Predicted weather conditions are shown for April 24-28. 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 Apr 19 and 25, and would be possible with wetting Apr 18, 23 and 24. Streptomycin is recommended to be applied today or tomorrow, Apr 24 or 25, and for any regular spray application when wetting is the only factor lacking for infection. Also, remember to protect young and recently planted trees, which have flowers but might be considered to be "non-bearing". Fire blight risk should subside with cooler predicted temperatures Apr 26-28. The BBS column is tracking the appearance of blossom blight symptoms from infection that occurred Apr 19. Symptom appearance is predicted when this value reaches 100.

Below 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 4/13/2019. Cougarblight shows color-coded risk assessments as “Cougarblight 4-Day DH” and infection potential EIP value. This risk is "high" for Apr 23, 24 and 26 and "extreme" or infection tomorrow, Apr 25, and also with infection possible with a trace of wetting from rainfall today, Apr 24, so the current predictions are similar for the Cougarblight and Maryblyt models. 
Graphic from the NEWA/Cougarblight model, April 24, 2019. Click to enlarge.

Note that real fire blight risks can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a streptomycin application is more effective when applied ahead of predicted infection.

Monday, April 22, 2019

Apple scab and rust infection Apr 19-20; fire blight outlook this week

We recorded another apple scab and rust infection period at Winchester Apr 19-20: 13 hr wet at 62° with 1.01 inches of rain. Considering the timing of this infection period while flowers are highly susceptible to quince rust infection, it is prudent to include an SI  fungicide for after-infection control of rusts in the next spray application. Similar wetting and temperature conditions occurred east of the Blue Ridge and southward to Roanoke and beyond. Such conditions were also favorable for infection by peach scab on small fruits which are now vulnerable after the "shuck-split" stage.
Also, we have had 9 days favorable for powdery mildew infection since mildew spores were available Apr 6.

Fire blight outlook for Winchester: Below is a cropped graphic from the Maryblyt 7 program. Apple trees are now near full bloom in the Winchester area. The temperature and rainfall data are current through Sunday evening, April 21. Predicted weather conditions are shown for April 22-26. 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. 
Graphic from Maryblyt 7, April 22, 2019. Click to enlarge.

Based on recorded temperatures and wetting, the risk column shows that infection was possible Apr 19. and risk remained high high for Apr 20, but subsided Apr 21-22. Note that the EIP is near 100 or above for Apr 23-26, so a slight increase in temperature or wetting this week could change the risk factors that are lacking (EIP of 100, average temperature of 60,wetting). As it stands, a special caution is in order for Apr 25 when only wetting is lacking for infection. Because any spray application can serve as the wetting trigger, include streptomycin with any spray applied under such conditions through late bloom. Also, remember to protect young and recently planted trees, which may have flowers but might be considered to be "non-bearing". The BBS column is tracking the appearance of blossom blight symptoms from infection that occurred Apr 19. Symptom appearance is predicted when this value reaches 100.

Below 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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH”. This risk is "caution" for Apr 22 and "high" for Apr 23-26. Note that if we were to select "Fire blight is now active in your neighborhood" as the orchard blight history, "caution" becomes "high" and "high" becomes "extreme".  The difference in EIP level shown for Apr 20 in this graphic compared to the Maryblyt graphic above is related to the temperatures that were entered on Apr 18-19 (not shown in the Cougarblight graphic). 

Graphic from Cougarblight, April 22, 2019. Click to enlarge.

Note that real fire blight risks can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.

Friday, April 19, 2019

Possible fire blight, scab and rust infection today

NOTE: This year for fire blight risk assessment, we are again comparing posted graphics from Maryblyt 7, as in previous years, with those from the Cougarblight model as shown on our NEWA site. We will be using the same recorded weather data from our NEWA station to make these comparisons. 

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 Maryblyt, April 19, 2019. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most cultivars are now have bloom with some near full bloom in the Winchester area. The temperature and rainfall data are current through Friday morning, April 19. Predicted weather conditions are shown for April 19-23. 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 high risk for Apr 13 and 16, but with an EIP less than 100; by Apr 18 the EIP reaches 100, but wetting is lacking. Apr 19 shows a significant risk of infection with all infection criteria met. For such situations a spray of streptomycin is recommended by Apr 19. With cooler temperatures Apr 20-22 risk should subside, but will again begin to increase with warmer temperatures Apr 23. The BBS column in the Maryblyt graphic is tracking the appearance of blossom blight symptoms from infection that occurs today, Apr 19. Symptoms appearance is predicted when this value reaches 100.

Below 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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is "caution" for Apr 18 and "high" for Apr 19-22. This is a rather important difference between the two predictive models. Note that this graphic would indicate "extreme" risk if today's EIP were 100, but it is 99, not quite triggering the "extreme" risk. Caution: Both of these models are a guide to fire blight risk, and the EIP shown in the graphic below is very close to infection conditions with rain today Apr 19. 
Graphic from Cougarblight 7, April 19, 2019. Click to enlarge.

Risk can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Apr 22.

Also note that apple scab, cedar-apple rust and quince rust infection are likely today, with locally heavy rainfall expected during the day and continued wetting through tonight.

Powdery mildew is now active. Mildew conidia have been available for infection at our AREC since Apr 6. Any “dry weather“ day above 53° is suitable for mildew infection, and we have had seven mildew infection days since Apr 6.

Wednesday, April 17, 2019

Increasing fire blight threat Apr 18-19!

NOTE: This year for fire blight risk assessment, we are again comparing posted graphics from Maryblyt 7, as in previous years, with those from the Cougarblight model as shown on our NEWA site. We will be using the same recorded weather data from our NEWA station to make these comparisons. 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 Maryblyt 7, April 17, 2019. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most cultivars now have some bloom open in the Winchester area. The temperature and rainfall data are current through Wednesday evening, April 17. Predicted weather conditions are shown for April 18-22. 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 high risk for Apr 13 and 16, but with an EIP less than 100; by Apr 18 the EIP reaches 100, but wetting is lacking. Apr 19 shows a significant risk of infection with all infection criteria met. For such situations a spray of streptomycin is recommended on Apr 18 or 19. Cooler temperatures Apr 20-22 should reduce fire blight risk.

Below 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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is "caution" for Apr 18 and "high" for Apr 19-22. This is a rather important difference between the two predictive models. The apparent unusual difference in amount of risk predicted by Maryblyt and Cougarblight is because the EIP does not reach 100 (only 85) in Cougarblight but in Maryblyt it is 103 on Apr 18 and 116 on Apr 19 due to higher daily average temperatures, especially for Apr 18.
Graphic from Cougarblight, April 17, 2019. Click to enlarge.

Risk can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. The fire blight outlook will be updated Apr 19.

Monday, April 15, 2019

Apple scab and rust infection period Apr 14-15

We recorded another apple scab and rust infection period at Winchester Apr 14-15: 14 hr wet at 62° with 0.53 inches of rain. This was another critical cedar-apple rust and quince rust infection period with many spores released during the extended wetting period, and flowers highly susceptible to quince rust infection. Considering this infection period following the recent one Apr 12-13, it is prudent to include an SI (DMI) fungicide for after-infection control of rusts in the next spray application. More rainfall and infection is expected Apr 19-20. 

Infection conditions were similar southward to Roanoke and east of the Blue Ridge from Manassas to Central Virginia. Rainfall amounts since Apr 12 ranged from 1.5 to nearly 2 inches. This was enough to deplete protective fungicide residue, and fungicides with after-infection control are suggested.

Previously, I posted a picture of a large quince rust canker, which illustrates the perennial nature of quince rust inoculum levels. Thus, serious quince rust epidemics are dependent on the release of spores while the blossoms are susceptible, the condition that has just occurred over the past several days. Below is a contrasting picture that shows a small quince rust canker on third year growth and tiny cedar-apple rust galls (upper left) with a single spore horn protruding. These were obviously produced on last years new green foliage on the cedar tree. However, both contribute to overall rust inoculum levels.

Sporulating quince rust canker (lower right), and small cedar-apple rust galls (upper left).
 

Sunday, April 14, 2019

Fire blight outlook at Winchester this week

King bloom on Idared, Apr 14, 2019.

NOTE: This year for fire blight risk assessment, we will again compare posted graphics from Maryblyt 7 as in previous years, and also from the Cougarblight model as shown on our NEWA site. We will be using the same weather data from our NEWA station to make these comparisons. 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 Maryblyt 7, April 14, 2019. Click to enlarge.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. We will use Saturday, Apr 13 as the date of first bloom open on early cultivars such as Idared and Pink Lady. The temperature and rainfall data are current through Sunday evening, April 14. Predicted weather conditions are shown for April 15-20. 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 high risk for Apr 13, 15, and 16, but lacks the required EIP of 100. Entering an earlier bloom date did not raise the EIP for Apr 13, and did not raise the risk of infection. With cooler predicted temperatures mid- week, fire blight risk should be low to moderate Apr 17-18. However, with warmer than predicted temperatures, expect the risk to increase again.

Below 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 4/13/2019. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is low for Apr 14-16.
Graphic from Cougarblight, April 14, 2019. Click to enlarge.
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. The fire blight outlook will be updated Apr 17.

Saturday, April 13, 2019

Heavy apple scab and rust infection period Apr 12-13

In Winchester, we recorded a heavy apple scab and rust infection period Apr 12-13: 22 hr at 60°, with 0.77 inches of rain. Many cedar-apple rust and quince rust spores were released during this extended wetting period, and flowers are near their peak susceptibility for quince rust infection. In areas where there is a concern for rust infection, include an SI (DMI) fungicide in the next spray application. More wetting at warm temperatures is expected Apr 14-15. 

Apple scab infection conditions were similar to Winchester's southward in the Shenandoah Valley and east of the Blue Ridge to Central Virginia, but with slightly warmer temperatures and up to 1.8 inches of rain in some areas-- enough to erode the protective fungicide residue during the wetting event. 

Powdery mildew conidia have been available for infection at our AREC since Apr 6. Any “dry weather“ day above 53° is suitable for mildew infection. So far, we have had four mildew infection days.

The huge quince rust canker below seen recently in Frederick County has likely been producing rust basidiospores for 25 years or more. Its leaves were infected when it was only a couple years old and now it has a trunk diameter of 5-6 inches.



Sporulating quince rust canker on eastern red cedar. Photo by Mark Sutphin.

Saturday, April 6, 2019

Apple scab infection April 5-6.

The first general apple scab infection occurred in the Winchester area and east of the Blue Ridge from Rappahannock County and south to Lynchburg April 5-6. At our AREC in Winchester, scab ascospores were released, and we recorded 33 hr of wetting at 40-47° F with 0.5 in. of rainfall. Many apple cultivars such as Cripps Pink, Red Delicious, Gala (shown below), and Idared are in the tight cluster stage, and presented a sizable target of exposed green tissue for scab infection. Hopefully, there was opportunity to apply protective fungicides prior to this infection.


Gala apple buds at tight cluster stage at Winchester 4/6/19.

Cedar-apple rust gall spore horns (shown below)  are expanding and will probably discharge the basidiospores that infect apple with the next wetting period. By tight cluster stage powdery mildew spores are usually available for infection, which occurs on dry days above 53° F

Cedar-apple rust gall at Winchester 4/6/19
Where the bud stage is more advanced to pink or open blossoms, as in central Virginia and the Roanoke area and south, be alert for fire blight infection with warmer weather and shower or thunderstorm activity this week.

Friday, March 22, 2019

New season- Old question

Early tight cluster stage, Cripps Pink, central Virginia 3/20/19
The picture above was sent to me with the question,"Is it too late for a copper spray"? The short answer is "Yes, at this stage, it's too late for a copper spray on fresh market fruit. 

The explanation is that at tight cluster stage, among the flower cluster leaves you can begin to see the sepals and what will develop into the fruit. Because this is exposed, it is likely that copper will cause russet at this stage and would not be recommended. For processing fruit, where fruit finish is not a concern, copper applied at this stage will be a protectant fungicide for control of early scab infection and as a suppressant for later build-up of fire blight bacteria emerging from overwintering cankers.

At Winchester on Thursday Mar 21 we could see the earliest green tip on Red Delicious and this would be the ideal timing for copper application.

Our AREC NEWA weather station indicates early maturity (1%) of scab ascospores and this, coupled with wetting and temperature conditions, could result in early scab infection where unprotected green tissue is exposed. The Gadino Cellars NEWA station in Rappahannock County also indicates scab infection with 1% spore maturity and also forecasts possible infection for Mar 24-25. Scab infection is also predicted for Mar 25 for the Roanoke and Lynchburg areas, with 2-4% of scab ascospores mature. 

Saturday, July 28, 2018

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

Thursday, July 5, 2018

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.