Glomerella leaf spot- New to Frederick County

Yesterday morning I was called to check a block of Golden Delicious trees that are losing one-third or more of their leaves. Before the morning was over I had observed symptoms of Glomerella leaf spot, a rapidly expanding disease, at our AREC and in five other orchards within two miles of our AREC. I also received an e-mailed image of the same problem from Rockingham County. Diagnostic symptoms (shown below), include leaf spots with concentric rings on Gala, Golden Delicious, and Cripps Pink (Pink Lady). The lesions start as purple spots, then growth with concentric rings, and may eventually coalesce. Symptoms may appear on both old and younger leaves and leaves may yellow and fall off.

Glomerella leaf spot. Early lesions are small purple, irregular spots (at bottom) which typically enlarge with concentric growth rings that may coalesce. Lesion enlargement and concentric rings may be due to secondary fungi.

Typical appearance of leaf yellowing caused by Glomerella leaf spot.



Glomerella leaf spot and fruit rot from Nelson County VA, 2011


Glomerella leaf spot was reported in TN in 1998. It built up in NC in 2004 and became more prominent with wet weather in ’05. The following winter I began to receive reports from growers and consultants who thought they may have seen it in southern VA. It became prominent again in southern VA/NC in 2010 and caused some problems in Nelson County, VA in 2010-11.



Fruit rot symptoms caused by Glomerella cingulata, a stage of the bitter rot fungus, tend to be darker than those usually associated with bitter rot. The rot spots often remain small but, like typical bitter rot, the fruit rot caused by the Glomerella strain has a cone-shaped pattern of growth into the fruit.



Recommendations for control as we approach harvest depend on market plan for the affected variety and the days to harvest. Pristine is the single most effective material that may be applied close to harvest. Other possible options include Flint + Captan and Captan + potasssium phosphite.

Leaves are an important overwintering site and overwintering inoculum can be reduced by shredding leaf litter with a flail mower or applying a foliar spray of urea at leaf drop. This can also aid in suppressing other foliar diseases such as apple scab and Alternaria leaf blotch.

WEEKEND WETTING: Split extended wetting periods of 14 hr and 10 hr occurred with a total of 0.75 inch of rain at 70° Aug 25-27. We also had several nights of heavy dews last week, bringing the accumulated wetting hour total from rainfall or dew since Apr 18 to 909 hours.

Extended wetting and summer disease pressure

Nine hours of extended wetting occurred with an 0.06 inch of rain at 69° Aug 14. We also had several nights of heavy dews last week, bringing the accumulated wetting hour total from rainfall or dew since Apr 18 to 835 hours. This total, generally indicative of sooty blotch and flyspeck pressure, is the highest for this time last year since 2003.

Bitter rot and some other rots have appeared on poorly protected apple fruit that were damaged by hail on July 31.

More summer disease weather

Summer disease pressure remained high this week with several nights of heavy dews and with 14 hours of extended wetting with an inch of rain at 69° Aug 9-10.

I was away for a week, and on my return some changes were obvious- lots of apple trees with light green, new growth, and nice red color on ripening (and tasty!) Gala apples.

Where powdery mildew is a problem, the new growth will be susceptible to mildew infection, leading to more overwintering. In such situations, the fungicides Indar and Inspire Super offer some suppression of mildew and other summer diseases such as sooty blotch and flyspeck. Both Indar and Inspire Super have restrictions preventing their application closer than 14 days to harvest. We suggest including a general protectant fungicide such as captan or ziram with the above fungicides to broaden the spectrum and residual activity.

Yesterday I saw striking examples of the effects of fire blight strikes on the prevalence of bitter rot in Nittany apples (shown below). The bitter rot fungus can colonize the dead twigs within six weeks of the initial fire blight blossom infection and become a bitter rot inoculum source for the rest of the year. Any fire blight strikes in a tree should be taken as a warning of a potential rot problem. Notice that the fruit immediately below also has sooty blotch, and that indicates that protective fungicide is lacking which would also permit more rot problems.

Extended wetting August 5-6.

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

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

Heavy rainfall and extended wetting event July 31

We had rainfall of 2.5 inches and 17 hours extended wetting at our AREC Jul 31-Aug 1. Most of the heavy rainfall occurred in mid-afternoon and it included scattered hail. But there were additional showers in the evening that extended wetting throughout the night. Mean temperature was 67°.

Most protective fungicides will not weather through 2 inches of rain, and favorable temperatures with some hail injury are likely to increase the potential for fruit rots as well as sooty blotch and flyspeck. 

Extended wetting occurred July 20-21 with 19 hours wet at 66° and 0.34 in. rain. Accumulated wetting hour total from rainfall or dew since Apr 18 is now at 615 hours, 225 hours ahead the total for this time last year.

Recent extended wetting periods

This past week we had three extended wetting periods and more than 2.5 in. of rain (as of 4 PM today, but we are really not complaining about the rainfall): Jul 15-16, 10 hr wet at 70°; Jul 18-19, 8 hr wet at 71°; Jul 19-20, 17 hr wet at 72°. In the past two weeks we have gotten more than 4 inches of rain, which would have eroded most protective fungicide residues, adding considerable rot pressure on apples and other fruits. Cumulative wetting hours now stand at 572, the highest total for this time of the year since 2003, and the fourth highest total since 1994.


There have been several reports of rots appearing where was earlier fire blight infection. This should be expected because any dead twigs can be quickly colonized by several rot fungi, leading to a build-up of inoculum and subsequent infection under the warm and wet conditions such as have occurred recently.


Scout for sooty blotch and flyspeck in lower elevation areas where you typically see these problems first, and make appropriate management adjustments as needed.

Some much-needed rainfall July 8-9

Scattered and repeated thunderstorms brought varying amounts of rain and some hail to parts of Frederick County July 8-9. At our AREC, we recorded 1.4 inches of much-needed rain and 16 hr wetting at 72 degrees. We have noticed brown rot on green nectarines, an indication of increasing fungal activity as peaches and nectarines are approaching harvest.

Extended wetting periods and summer disease development

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


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

Extended wetting and summer diseases

Extended wetting occurred June 18-19 with 15 hours wet at 64° and 0.11 in. rain. With this and other wetting in the past week, the accumulated wetting hour total from rainfall or dew since Apr 18 is now at 413 hours. 

Sooty blotch was first observed in non-treated trees at our AREC June 13, indicative of this year's early summer disease pressure.

Extended wetting and validation of the sooty blotch flyspeck wetting hour threshold

Extended wetting June 11-13 involved two combined wetting periods of 14 hours at 69° and 12 hours at 66° with a total of 1.4 in. rain. These wetting periods favored secondary scab and all summer diseases on apples and brown rot on ripening stone fruits. Accumulated wetting hour total from rainfall or dew since Apr 18 is now at 367 hours. 


Because of early bloom and petal fall this year, there had been some questions about using the Apr 8 petal fall date as the trigger for accumulating wetting hours, starting 10 days later. The 250 accumulated wetting hour threshold is used to predict the presence of sooty blotch/flyspeck (SBFS) fungi on unprotected fruit. Using the Apr 18 date we had passed the 250-wetting hour threshold by May 25, four weeks ahead of last year and the second earliest date for reaching this predictive threshold on record since 1994. We are now seeing SBFS on fruit samples collected at our AREC three weeks ago and incubated under high humidity since then. This indicates that fungi were present May 25 and confirms the validity of the Apr 8 petal fall date and Apr 18 as the accumulation date in spite of this year's early bloom and petal fall dates.

Extended wetting June 1-2 and accumulated wetting

Extended wetting June 1-2: 12 hours at 63-51° brought the accumulated wetting hour total since Apr 18 to 319 hours. This is still a month ahead of last year's total. 

Extended wetting periods May 27-30 and accumulated wetting hours

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


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

Extended wetting May 24-25

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

Infection period May 23-24

Last night's wetting (12 hr at 63° with 0.04 in. rain) qualified as a scab infection period. 

This wetting brought the accumulated wetting hours since Apr 18 to 234 hours. In the next couple days it is likely that we will reach the 250 wetting hour threshold for specific treatment against the sooty blotch/flyspeck fungal complex. This would be the second earliest week for reaching this predictive threshold since we began recording this in 1994. Only 2003 was earlier. This signals early summer disease pressure from the sooty blotch/flyspeck fungal complex as well as other "summer diseases" and Alternaria leaf blotch.

As expected, there are early indications of heavy brown rot pressure on ripening cherries.

Infection periods May 21-23

Scab infection periods occurred May 21-22 (22 hr at 67°) and May 22-23  (12 hr at 64°). Total rainfall for these two events was 0.26 in. at our AREC but some other areas of Frederick County received considerably more rain volume, especially on the evening of May 22. 

These wetting periods at relatively warm temperatures could signal early summer disease pressure. Through this morning we had accumulated 222 wetting hours since Apr 18, rapidly advancing toward the 250 wetting hour threshold for specific treatment against the sooty blotch/flyspeck fungal complex.

Cherry leaf spot symptoms were observed today.

Early season disease update; sooty blotch and flyspeck wetting hour accumulation

A scab and cedar-apple rust infection period occurred May 13-15 (26 hours wet at 61°, 0.4 in. rain). There was still cedar rust inoculum available for foliar infection but galls are now mostly depleted at our AREC. If you have a recurrent cedar-apple rust problem in your orchard, check the cedar galls in your area for remaining inoculum potential with wetting today.

Through May 20 there have been 38 days favorable for powdery mildew infection since spores were first available Mar 19. Secondary scab and mildew infection are heavy on non-treated trees.

Some shoot blight was reported last week, resulting from scattered hail in some areas of Frederick County May 2. These "trauma blight" symptoms appeared near the time predicted by Maryblyt for May 15. Numerous early reports of fire blight have come from areas east of the Blue Ridge and the Roanoke area south. These likely occurred as blossom infection where bloom was open earlier than in the Winchester area.

For purposes of predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours, starting 10 days after petal fall. With the extended bloom period this year, the petal fall date was somewhat subjective, but we have settled on Apr 8 for petal fall. So the start of wetting hour accumulation will be from Apr 18, 20 days ahead of last year and 11 days ahead of 2010. Through this morning we have accumulated 189 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex.

Scab and rust infection periods May 5 & 8

Wetting periods favorable for scab and cedar-apple rust infection occurred May 5-6 (13 hours wet at 63°,< 0.01 in. rain) and May 8-9 (split wetting, 18 hours at 64°, 0.4 in. rain). There are still plenty of active rust galls giving off inoculum for foliar infection. Fruit are no longer susceptible to rust infection.

Through May 10 there have been 30 days favorable for powdery mildew infection since spores were first available Mar 19.

There was scattered hail in some areas of Frederick County May 2 and fire blight shoot symptoms related to trauma blight infection are predicted to appear May 15.

The above wetting periods were also favorable for scab infection on peaches and nectarines.

Disease update for the weekend

The recent fire blight scenario unfolded not too far off of that shown in the graphic below for Apr 28. Briefly put, based on recorded and predicted temperatures, any day with wetting from May 1 through May 11 is a potential fire blight infection day where flowers persist. There is still susceptible bloom on Romes, York and Nittany, and some other varieties such as Golden Delicious and Gala, some of which may have been initiated in response to frost injury March 27. Some of these days will have wetting from rain or dew; others will have wetting from thinning or maintenance sprays. On May 2 there was scattered hail that may have caused a trauma blight situation in some areas of Frederick County

Powdery mildew pressure remains high this season, with 26 days favorable for infection through Apr 30. With recent warmer temperatures and more rapid shoot growth, secondary infection is evident and foliage susceptibility very high. Shoots showing secondary infection are likely to have infected lateral buds that will become overwintering inoculum sources for next year's mildew epidemic.

Wetting periods at our AREC this week have been close for secondary scab but not quite long enough for cedar-apple rust infection of foliage. Fruit at thinning size are no longer susceptible to cedar or quince rust infection. There is still a lot of inoculum present on cedar rust gall spore horns.

Fire blight update

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.

(Click on image to enlarge)

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Some cultivars still have some susceptible late bloom. Here is a prediction for trees with lingering bloom. (A month ago, who would have thought that we would see any bloom at Shenandoah Apple Blossom Festival time next weekend?). The temperature and wetting data were current through yesterday afternoon, Apr 27. Predicted weather conditions are shown for Apr 28-May 5. 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). The risk column shows that fire blight infection could have occurred with wetting by dew Apr 20, and with any wetting of late bloom by rain, a spray application, or heavy dew Apr 15-17. After a ten-day decline, risk could again increase to an infective level with wetting May 2-5. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection and with any spray applications of other materials. Be aware that risks can abruptly increase with unpredicted warmer temperatures and wetting. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 20) and canker blight symptom appearance, respectively. Those symptoms should begin to appear about May 6. The numbers represent percent of required degree hours for symptom appearance. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Disease update

It has been mostly wet since Saturday afternoon, Apr 21, with soaking rainfall totaling 0.9 in. Wetting Saturday likely resulted in quince rust infection of unprotected susceptible blossoms and cedar-rust infection of foliage and some fruit; fruitlets which have reached thinning size should be relatively resistant to quince and cedar rust rust infection. Wind direction during the early wetting was mostly from the west and northwest, a warning regarding the cedar tree inoculum source for rust-prone orchards. The current 24+-hr wetting period favors secondary scab.

Secondary powdery mildew lesions were common by Apr 20, evidence of our most active early season disease this year.

The fire blight outlook remains similar to that posted below, but with risk Apr 23-29 now showing as only light or moderate. However there is still susceptible bloom on many cultivars, especially in lower areas where there was frost damage, and there will probably still be some late bloom when temperatures are again warm enough to expect some risk from fire blight (Stay tuned!).

Fire blight update

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.

(Click picture to enlarge)

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Many cultivars still have some susceptible bloom. Here is a prediction for trees with first bloom open Monday, March 23, 2012. The temperature and wetting data are current through this morning, Apr 20. Predicted weather conditions are shown for Apr 20-29. 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). The risk column shows that fire blight infection could have occurred with any wetting from rain, a spray application, or heavy dew Apr 15-17. After a two-day decline, risk has again increased to an infective level today. After tomorrow, predicted cooler temperatures Apr 22-27 should suppress risk to low to moderate levels. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection and with any spray applications of other materials. Be aware that risks can abruptly increase with unpredicted warmer temperatures and wetting.  This graphic will be updated Apr 23. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.