Some late season reminders

 

A late season scab build-up would increase inoculum levels for 2014

Fall urea spray to reduce overwintering disease inoculum.
The scabby leaf pictured above indicates a potential build-up of late season scab. It was on a tree that had been treated with protectant fungicides every two weeks through Aug 30. Harvest season in the Winchester area was relatively dry-- until October 10-14 when we got 3.6 in. of rain. By that time most commercial orchards were unprotected and the cool temperatures during those rains were optimal for scab development on the underside of leaves after the fungicides were gone. Such infection will overwinter and increase ascospore levels next spring.

A foliar urea spray is recommended as a supplemental application at early leaf drop to encourage more rapid leaf breakdown and reduce overwintering of leaves with apple scab, Glomerella leaf spot and Alternaria leaf blotch inoculum. The recommended rate is 40 lbs of urea per acre, applied to wet the remaining leaves on the tree and with nozzles also directed to cover leaves already on the orchard floor, under the trees and in the adjacent row middles. This practice has been shown to reduce scab inoculum by as much as 95%, thereby reducing the threat of heavy early season infection next spring. Special consideration should be given to this approach where resistance to strobilurin (QoI) and sterol-inhibiting (SI) fungicides is suspected. Glomerella leaf spot was a new problem in the Winchester area in 2012 but not as much of a problem in area orchards this year; however this year it remained a serious problem east of the Blue Ridge, in southern Virginia and western North Carolina.





Bacterial spot on Galaxy "flat" peach

Bacterial spot- Note angular lesions



Bacterial leaf spot of peach: The leaf spot bacteria overwinters in small twig cankers caused by infections at the leaf abscission scars soon after leaf drop. Where bacterial leaf spot has been a problem, apply a copper spray at early leaf drop to protect those leaf abscission scars thereby reducing the potential for infection next year. A copper spray in the fall (or any time before bud swell in the spring) also serves as the peach leaf curl spray.

Pay attention to abnormal foliage color of trees in a planting: Early, reddish/purplish coloring of foliage often signals a problem with the lower trunk or crown area of that tree. This year we saw some increase in collar rot problems, but such symptoms could also be caused by voles, dogwood borers, or more than one of these problems. All have specific treatments that improve control and reduce tree loss but need correct diagnosis and treatment to expect effective results. It could also be fire blight in the rootstock of M.9, M.26 or Mark rootstock if there was earlier infection in the planting. There isn't much that can be done for a tree dying from fire blight in the rootstock but it should be recognized and noted for improving control measures for next year. This includes thoroughly cutting out overwintering inoculum cankers during the winter and by being ready to protect the planting with copper at early green-tip and with streptomycin as needed at bloom.

A final reminder for the year: As usual, make notes, based on harvested crop, of disease or insect problems that affected quality yield in individual orchard blocks this year, and develop management strategies to address these problems at appropriate times next year.

Recent extended wetting periods resulting in potential rot activity

Significant summer disease pressure continues with extended wetting periods occurring Aug 17-18 (16 hr with 0.16 in. of rain at 61°), Aug 21-22 (14 hr with 0.05 in. of rain at 66°) and a serious one for rot activity this week, Aug 28-29 (30 hr with 0.42 in. of rain at 71°).

As of Aug 26 accumulated wetting hours totaled 655, approximately equal to or more than that for seven of the past ten years.

Disease management and pre-harvest sprays in the orchard directly affect postharvest quality and storage rot problems. Maintain intervals of pre-harvest fungicides appropriate to disease pressures and the prevailing weather conditions, but allow flexibility in pre-harvest intervals for your intended fruit market.

Continued summer disease pressure

We are seeing continued summer disease pressure with extended wetting periods last week occurring Aug 5-6 (11 hr with 0.3 in. of rain at 63°), Aug 7-8 (18 hr with 0.34 in. of rain at 74°) and Aug 8-9 (16 hr with 0.12 in. of rain at 73°). Also, the 78 wetting hours last week brings our accumulated wetting hours since May 13 to 549.

So in the first two weeks of August we have had five extended wetting periods, with three of these at relatively warm temperatures (more than 73°), which has given significant pressures for apple rots, and sooty blotch and flyspeck, and possible leaf spot diseases, and certainly for brown rot on ripening peaches. 

Disease management and pre-harvest sprays in the orchard directly affect postharvest quality and storage rot problems. Maintain intervals of pre-harvest fungicides appropriate to disease pressures, the prevailing weather conditions, and the intended fruit market.

 

Our congratulations to Frederick County Virginia grower Cordell Watt, Timber Ridge Fruit Farm, on his selection by American Fruit Grower as 2013 Apple Grower of the Year!
 

Apple and peach disease update

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

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

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

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

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

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



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

Summer disease update

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

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

Disease update

Three extended wetting periods of 10-11 hours occurred July 11-14 last week; total volume of rainfall for the week was 1.06 in. These wetting periods averaged in the upper 60s and lower 70s and were favorable for summer disease development.

As of yesterday morning, July 15, at our AREC we had accumulated 345 wetting hours, well beyond the 250-hr threshold. Last week sooty blotch/flyspeck symptoms were readily apparent on non-protected trees in our fungicide test blocks. By now it might be showing up in poorly protected commercial blocks as well.

I have been away for two periods of more than a week twice in the past month, and being away for a week seems to suddenly bring out some readily visible changes that appeared while I was away. Three weeks ago I noticed that more fireblight had shown up. A lot of this was advancement of symptoms from blossom blight on late, unprotected bloom; others appeared to be from shoot tip infection (shoot blight) related to secondary infection during storms.

Another change three weeks ago, but even more obvious this week, is the intensifying orange glow from cedar-apple rust on unprotected backyard York Imperial apple trees. York is very susceptible to cedar-apple rust, and even moderate amounts of infection can significantly reduce return bloom and yield the following year. It will be interesting to see how much bloom is present on these heavily infected trees next year. Two or three sprays of the readily available Immunox fungicide from mid-April to mid-May would have prevented most of this problem.

At risk of jinxing what appears to be a good corn crop coming on, I will say that it is always a good indicator of what the weather was like in the past couple weeks. Three weeks ago I was sure it had grown 2 feet in a week; now this week it is tall and all in tassel.

By the way, our hike in Glacier Park turned up more hawthorn rust than grizzlies!

 

Sooty blotch and flyspeck on non-protected fruit; rot weather

As of yesterday morning, July 8, we had accumulated 293 wetting hours and sooty blotch/flyspeck symptoms were readily apparent on non-protected trees in our fungicide test blocks.

Extended wetting periods last week occurred July 1-2 (8 hr with 0.03 in. of rain at 71°) and July 7-8 (18 hr with 0.97 in. of rain at 70°). These wetting periods were favorable for rots.

Last week's extended wetting and accumulated wetting hours

Last week was relatively dry, but with a 13-hr wetting period of June 29-30 with 0.14 in. of rain at 67°.

As of this morning, July 1, we had accumulated 251 wetting hours- just exceeding the 250-hour threshold for specific treatment against the sooty blotch and flyspeck fungal complex. For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. At 250 hours the organisms causing sooty blotch and fly speck symptoms are expected to be present on non-treated fruits, and symptoms will appear after a brief incubation period. Typically, symptoms will appear earlier in orchards at lower elevations where more wetting hours accumulate.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. As of this morning, June 24, we had accumulated 221 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

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

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

An uncommon apple fruit disease

This week an apple sample from Frederick County Virginia was brought to our laboratory with a problem that is unusual but not unheard of: Phytophthora infection of low-hanging, green fruit. Phytophthora cactorum is a causal organism of collar rot of apple but also infects several other hosts. Note the zoned appearance of symptoms on some fruits, likely a result of the effects of light and dark on its growth pattern. 

It is likely that swimming "zoospores" splashed up from the soil surface with heavy wind-driven rains and caused this infection within the past two weeks. EBDC fungicides, applied in the early cover sprays, should have helped to suppress this occurrence, although the residues would wear off quickly with heavy rains.

Disease update, June 17

Extended wetting occurred June 12-13 with 11 hours wet at 68° and 0.41 in. rain. As of June 17, accumulated wetting hour total from rainfall or dew at our AREC since May 13 is now at 172 hours . Wetting hours have accumulated more rapidly east of the Blue Ridge. As of June 12 Washington, VA, in Rappahannock County had 286 hours of accumulated wetting since May 13. Other areas in central Virginia probably had as much or more during this time.

In areas with heavier disease pressure, watch for early indications of sooty blotch and flyspeck, fruit rots and Alternaria leaf blotch, the fungal disease that causes defoliation and poor fruit quality of Red Delicious apples, and Glomerella leaf spot, which tends to be more common on Gala, Golden Delicious, and Pink Lady. Maintain fungicide protection, as needed, to suppress the disease spectrum common to your orchard blocks.

Extended wetting June 10-11

Extended wetting from early yesterday morning through this morning (June 10-11) occurred as two separate periods of 12 and 16 hours, each at 65°; but with just four hours of drying between them, they might as well be added together, with total rainfall of 1 inch for both events. 

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

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

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

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

Disease update- apple scab, mildew and wetting hours

We recorded an apple scab and cedar-apple rust infection period at our AREC June 2-3: 18 hours wetting with 1.1 inches of rain at 74-62°. (Yes, the cedar-apple rust galls are still active).

As of today, June 3, we have had 38 dry weather apple powdery mildew days since spores were first released Apr 11. Today I see a flush of terminal shoot growth that is very susceptible to mildew under this year's heavy infection conditions. On susceptible cultivars, maintain mildew suppression until shoot growth ceases to prevent bud infection, which leads to overwintering and a recurrent problem next year.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours, starting 10 days after petal fall. This year the start of wetting hour accumulation is from May 13. As of this morning, June 3, we had accumulated 86 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. Last year we reached the 250-hr threshold May 25. Some areas east of the Blue Ridge may now be approaching the 200-hr mark for wetting hour accumulation.

Accumulated wetting hours for the sooty blotch/flyspeck threshold

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. This year we have settled on May 3 as our petal fall start date, so the start of wetting hour accumulation is from May 13, 25 days later than last year. As of Monday morning, May 27, we had accumulated 58 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. A caution to those further south and east of the Blue Ridge: Your petal fall date may have been a week or more ahead of ours and the earlier date would include the wet week of May 5, adding 80-100 more accumulated wetting hours to this total. Last year we reached the 250-hr threshold at our AREC May 25.

Scab and rust infection period May 23-24

We recorded another apple scab and cedar-apple rust infection period at our AREC May 23-24: 14 hours wetting with 0.8 inches of rain at 56-64°.

Recent infection periods

Cedar-apple rust galls are still actively supplying inoculum for foliar infection, but most fruits should now be resistant to quince rust. Apple scab and cedar-apple rust infection periods were recorded at our AREC May 18-19 (16 hours wetting with only 0.01 inches of drizzle at 56-64°), May 19-20 (10 hours wetting with 0.09 inches of rain at 63-67°), and last night, May 22-23 (18 hours wetting with 0.94 inches of rain at 62-70°). Secondary "sheet" scab is now common on trees that were not protected two weeks ago, May 6-11. 

As of today, May 23, we have had 29 dry weather apple powdery mildew days since spores were first released Apr 11.

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 May 3 as our petal fall start date. So the start of wetting hour accumulation will be from May 13, 25 days later than last year. As of Monday morning, May 20, we had accumulated 26 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. Last year we reached the 250-hr threshold May 25.

Fire blight alert-Take care of newly planted trees

Fire blight: With continued warm temperatures through next week, fire blight is predicted to remain at an infective EIP level through at least May 26. Any cultivar with bloom still open is susceptible, but, practically, late bloom is still a concern mostly on Rome Beauty apples.

Also, during this time, remember to take care of newly planted trees with flowers. The Zestar/ M9 tree, shown below, will have blossoms opening throughout the coming week.

Fire blight threat to late bloom wherever wetting occurs

With predicted warmer temperatures today, fire blight will be at an infective level wherever wetting occurs on susceptible blossoms, and is predicted to remain so through at least May 23. Wetting can be caused by rainfall, heavy dew, or by an airblast or dilute application of thinning, fungicide or insecticide sprays.

The Maryblyt graphic below shows 9-day predicted temperatures and wetting, and the risk column shows the fire blight infection risk history May 5-14 and predicted risk through May 23. Today, May 15, the EIP (epiphytic infection potential) reaches 117 (117% of the required) and remains higher than 100 through May 23. Also, the average daily temperatures remain higher than 60°F, the required minimum for infection to occur, throughout this period. So all that is required for susceptible bloom and wetting as indicated above.

The BBS column is tracking predicted appearance of blossom blight symptoms from infection May 10 to predicted symptoms (113a) May 21. The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, with canker margin symptoms (CMS) by May 15 and canker blight symptoms May 23. Canker advancement will not be prevented by a chemical treatment, and the presence of symptoms will indicate a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc.

CAUTION: Always beware that risks can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions, or with applications that cause wetting when all other infection conditions have been met. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by yesterday's site-specific data from SkyBit Inc.

Apple scab and rust infection period May 10-11

For the record, an apple scab and rust infection period was recorded at our AREC May 10-11: 18 hours wetting with 0.73 inches of rain at 60-64°

With predicted temperatures this week, fire blight risk is low to moderate May 13-15, then quickly returns to an infective level for late bloom May 16-17. For practical purposes, that will affect mostly the York Imperial and Rome Beauty cultivars, but check blocks carefully because Golden Delicious, Idareds, and others still have scattered pockets of susceptible bloom.  

Appearance of apple scab, cedar rust and fire blight symptoms

On May 10 apple scab and cedar-apple rust lesions from the Apr 17 infection period were readily apparent on unprotected trees at our AREC. The scab lesions were advanced enough that they were probably sporulating early this week, so that would indicate a secondary infection period during the extended wetting May 6-8 where control had been inadequate to prevent infection Apr 17. Secondary powdery mildew infection is also common on unprotected new shoot leaves.

Also, fire blight blossom cluster symptoms were easy to see from our experimental inoculations Apr 18, Apr 19, and Apr 23, but not yet from May 1.

Disease update May 9; threat of fire blight through the weekend

This week we have had a lot of disease activity, a heavy scab and quince rust and cedar-apple rust infection period at 46-57°, with 2.2 inches of rain from 10 AM May 6 to 8 AM May 8, and another scab infection period of 16 hours at 47-52° with 0.06 inches of rain last night. Scab lesions were present where trees were not adequately protected during the Apr 17 infection period. Most protective fungicides would have been depleted by the nearly 2 inches of rainfall associated with extended wetting May 7, leaving susceptible fruit and foliage vulnerable to infection by scab and the rusts, and also to powdery mildew. Since apple powdery mildew spores were first released Apr 11 we have had 20 days favorable for infection.

Fire blight symptoms were observed May 8 on Red Delicious blossom clusters in central Virginia. The fire blight outlook for the Winchester area for the next several days remains similar to what had predicted for these days since late last week. The Maryblyt graphic below shows that infection is possible with wetting May 8-10. Many cultivars still have susceptible bloom in the Winchester area and the moisture from an airblast application meets the wetting requirement to cause infection if all other other infection criteria have been met. 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.

Heavy scab and rust infection period in progress May 7

Since yesterday morning at 10 AM we have had 24 hr wetting at 54-56°, almost optimum for apple scab, quince rust and cedar-apple rust. Blossoms at petal fall are still very susceptible to quince rust infection so a follow-up including an SI fungicide in the next application is highly recommended (a "no-brainer"). Regarding potential rust inoculum source, winds during the wetting since yesterday have been from the north and east and appear to continue this way through today and tonight, then shift to a more southerly direction with continued shower activity tomorrow.

This will be a pivotal point in this year's scab epidemic. We will soon be nearing the end of predicted primary ascospore discharge, but lesions from our first infection period Apr 17 are expected to be appearing this week. So where control was good for the previous infection periods, we won't have too much to go till we can begin to focus on summer disease control, but where earlier control was inadequate, this infection period will be the source of continued headaches throughout May.

Yesterday was one of those unusual exceptions where there wasn't a forecast for rain early in the day, even with the Weather Channel's hourly predictions while it was raining! Today's SkyBit hourly report for our AREC for yesterday does not show leaf wetness until 4 PM but we had leaf wetness with showers at 10 AM, and leaves have probably remained wet since then.

I usually try to focus on our Winchester situation, where we have a better record of weather conditions, but it appears that those of you east of the Blue Ridge and farther south had similar conditions and substantially more rain than we did yesterday. Hopefully apples a little more advanced, with fruit at thinning time will be less susceptible to quince rust, but any trees with some blossoms in recent petal fall should be considered susceptible, and scatterred quince rust-infected fruits can hang on the tree and become a nuisance as a rot inoculum source as shown in the what-is-it blog below:  http://treefruitdisease.blogspot.com/2013/04/what-is-it-april-4-meeting-reminder.html

Fire blight outlook

As indicated by the Maryblyt graphic below, the fire blight outlook for this week remains similar to what was predicted last Friday: With warmer temperatures, risk will increase with EIP (epiphytic inoculum potential) by mid-week to the point where infection could occur with wetting Friday, May 10. Risk will remain at an infective level at least through May 12. Most trees in the area still have susceptible bloom, and some is likely to remain into the coming weekend.

The weather conditions used in the predictive part of this graphic are from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc.

Fire blight risk remains low. Have a great Shenandoah Apple Blossom Festival weekend!

This is Shenandoah Apple Blossom Festival weekend in Winchester, so for those of you in the area who want one more assurance that there will not be a fire blight problem until later next week here it is: As shown in the Maryblyt graphic below, predicted risk remains low through May 6, then becomes high as the temperatures rise and wetting occurs by May 8, with infection indicated on late bloom May 10-12. So, for now, go ahead and have a great BLOOM (or whatever)! The Maryblyt forecast will be updated May 6.

Apple scab/rust infection period Apr 29-30, and fire blight update

We recorded our third apple scab infection period Apr 29-30, with 18 hr wetting at 50-56°. This was also a likely quince rust and cedar-apple rust infection period.

FIRE BLIGHT: Below is the updated graphic from the Maryblyt 7 program. Based on 9-day predicted temperatures and wetting, the risk column shows the fire blight infection risk history through Apr 30 and predicted risk through May 9. The next four days, May 1-4, illustrate that the EIP (epiphytic infection potential) can gradually increase although the average daily temperature is lower than the of 60°F required minumum for infection to occur. This is because the EIP is based on estimated degree hours that the temperature is above 65°F throughout the day. Based on predicted temperatures, the EIP will approach the required threshold of 100 later next week (97% on May 9). Most cultivars are still near full bloom and some susceptible bloom will likely be present and should be protected if those conditions occur. The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, with canker margin symptoms (CMS) by May 8. Canker advancement will not be prevented by a chemical treatment and the presence of symptoms will indicate a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc.

CAUTION: As usual, be aware that risks can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. 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.

Apple scab infection period April 28-29

At our AREC we recorded split wetting periods totalling 18 hours starting at 54° at 11 AM Apr 28 and continuing at 50° throughout the duration of the wetting events. With expected high ascospore maturity and discharge, this is our most serious scab infection period this year. Hopefully, most blocks have received adequate fungicide protection up to this point and, with only 0.2 inch rain, should have been well protected through this event. Although the temperatures were a bit cooler than the optimum for the rust fungi, the blossoms are still very susceptible to quince rust and a follow-up application of an SI fungicide is advised where disease pressure is high and protection may have been lacking.

The outlook for fire blight infection over the next week remains low to moderate unless temperatures turn out to be significantly warmer than currently predicted. For the longer term, these cool temperatures will probably prolong the bloom period and our greatest threat of blossom blight may come on late bloom.

Since April 11 we have seen 13 dry weather, powdery mildew days, and we can expect secondary infection to be flourishing on new growth soon.

Continued reduced risk of fire blight in the Winchester area

FIRE BLIGHT: Above is an updated graphic from the Maryblyt 7 program. Based on predicted temperatures and wetting, the risk column shows that fire blight infection risk on Apr 29 is high with wetting but infection is not predicted, even with wetting, because the EIP (epiphytic infection potential) is now well below 100. With most cultivars near full bloom and later cultivars with early bloom open, this is a prediction for trees with first bloom open April 16, 2013. The temperature and rainfall data are current through Friday morning, Apr 26. Predicted weather conditions are shown for Apr 26-30. 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). Based on predicted temperatures and wetting, the risk column shows that fire blight infection risk on Apr 29 is high but infection is not predicted, even with wetting, because the EIP (epiphytic infection potential) remains well below 100. For infection to be predicted, wetting must occur after the EIP reaches 100 or higher.  Cooler predicted temperatures result in continued low EIP and reduced risk through May 3 (not shown). The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, 86% of the degree hour requirement by May 3. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will indicate a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc.


CAUTION: 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. This graphic will be updated April 29. 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.

Fire blight and powdery mildew/rusty spot update

FIRE BLIGHT: Below is a cropped graphic from the Maryblyt 7 program. Based on predicted temperatures and wetting, the risk column shows that fire blight infection risk on Apr 24 is high with wetting but infection is not predicted, even with recent wetting, because the EIP (epiphytic infection potential) is now below 100. With most cultivars approaching full bloom open and later bloom opening over the next several days, this is a prediction for trees with first bloom open April 16, 2013. The temperature and rainfall data are current through Wednesday afternoon, Apr 24, with showers predicted this evening. Predicted weather conditions are shown for April 25-29. 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). Based on predicted temperatures and wetting, the risk column shows that fire blight infection risk on Apr 24 is high with wetting but infection is not predicted, even with wetting, because the EIP (epiphytic infection potential) is now well below 100. For infection to be predicted, wetting must occur after the EIP reaches 100 or higher. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. Cooler predicted temperatures lead to a reduced risk Apr 25-29 and into next week (not shown). The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, 80% of the degree hour requirement by Apr 29. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will indicate a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc.
CAUTION: Be aware that predicted risk can change quickly with unanticipated warmer temperatures and wetting. This graphic will be updated April 26. 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.

Powdery mildew remains the most active among other apple diseases. Mildew infects during dry weather at temperatures above 53F. Since overwintering mildew spores were first observed on Apr 11, there have been nine day favorable to mildew infection. Rusty spot on peach is caused by the apple powdery mildew fungus, and with this much mildew activity underway, expect increased pressure by rusty spot on susceptible peach cultivars. Protective applications of myclobutanil (Rally) from petal fall through the early cover sprays are suggested for management of rusty spot.

Fire blight and other disease concerns

CAUTION: Based on weather data for our AREC, the fire blight prediction for Friday, Apr 19, remains at the infective level shown in the graphic posted below on Apr 16. If the cooler temperatures prevail as predicted in the ten-day forecast, infection after today is not likely well into next week. Streptomycin, applied Apr 17-19, should effectively cover for this infection event.

On Wednesday, Apr 17, we recorded 12 hours of wetting with slow drying conditions at 56-62° F, conditions favorable for apple scab, quince rust and cedar-apple rust. Blossoms are now very susceptible to quince rust, and for blocks that were not adequately protected for this infection period, it would be prudent to include an SI fungicide with strong after-infection activity in the next fungicide application. 

Powdery mildew has been the most active apple disease so far this year. Mildew spores were observed on new growth from overwintering buds Apr 11, and we have had infection conditions seven of the nine days since then. As early as pink stage, blossoms are highly susceptible to infection which causes the fruit russeting shown below. For mildew-susceptible varieties, include a fungicide with mildew activity in each application from tight cluster stage through to a month after petal fall.

Powdery mildew russeting of fruit can occur as early as pink stage.

Fire blight alert for this 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. 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.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With early cultivars with bloom open, and more bloom opening over the next several days, here is a prediction for trees with first bloom open today, April 16, 2013. The temperature and rainfall data are current through this evening, April 16. Predicted weather conditions are shown for April 17-20. 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). Based on predicted temperatures and wetting, the risk column shows that fire blight infection will be possible on open bloom if wetting occurs Apr 18-19. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. Cooler predicted temperatures lead to a reduced risk Apr 20-25. If first bloom opened Apr 17, infection would still be possible on Apr 19, but if first bloom did not open until Apr 18, the EIP would remain below an infective level through the weekend.

This graphic will be updated April 18, or sooner if significant change warrants it. 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.

Apple disease status

Today advanced Idared fruit buds were at open cluster stage, and some blossoms are likely to open in the next couple days. The picture below was taken during the wetting period April 12.

Apple scab, cedar-apple rust, and quince rust spores were mature Apr 12, but 12 hours' wetting was probably not quite long enough at 51-55° to cause significant infection by these diseases.

However, powdery mildew spores were also available under favorable dry weather infection conditions Thursday, Apr 11.

Oh yes, speaking of rust conditions, the mystery disease below was caused by one of the rusts, most likely quince rust. This resulted in small mummified fruits and a potential carry-over of bitter rot inoculum for fruit infection this year.

What is it? April 4 meeting reminder

This problem may not be what you think it is...

This is a reminder that our first In-Depth Meeting of the new season will be held at Alson H. Smith Jr. AREC, 595 Laurel Grove Road, Winchester, VA, starting at 7 PM Thursday, April 4. Following horticulture and entomology updates by Drs. Greg Peck and Chris Bergh, we will address this and other pathology questions and issues.

Here's another close-up example:

Scab spores and green tip

Apple scab ascospores were discharged at our AREC with showers starting yesterday morning. The earliest buds on Gala showed some green-tip, but 17 hours of wetting at 39-47° F was not enough for an infection period. It was a “two-minute warning” of sorts. Hopefully now, gradual bud advancement over the next week will allow some opportunity for application of protectant fungicides before another scab infection event. Preventive disease management is the best way to offset development of resistance to the more highly selective fungicides.

Idared apple blossoms - then and now

 On March 24 last year we were concerned about apple scab and rust infection and a threat of fire blight where blossoms had opened March 23. Today there's not much susceptible tissue out there and I'm ok with that! That white stuff on the nearly dormant buds isn't cotton. Can we say climate un-change?


But remember that the apple scab spores are just waiting their turn...

   

March 24, 2012

 

March 25, 2013



Prelude to a new season

The past several days we have seen a blanket of white in the orchards. This is great for holding back the rush of an early season and gets plenty of moisture into the ground. But this moisture on thawed ground will probably bring early scab ascospore maturity, so is it is important to be ready with protective fungicides. After application at green-tip stage, a copper spray will give about a week's protection against scab and also provides a deterrent to the buildup of fire blight bacteria before bloom.