Thursday, April 17, 2014

Apple scab and rust infection April 14-15

Ginger Gold apple bud stage, April 16, 2014

As shown above, apples at our AREC were mostly in open cluster bud stage Wednesday morning, April 16.

Scab and rust infection period:  We had about 13 hr wetting in the 59-64° range Apr 14-15, followed by another 10 hr wet as the temperature dropped from 55 to 38. This was plenty enough for scab, quince rust and cedar-apple and infection.

As usual, we saw powdery mildew spores emerging from tight cluster stage buds last week, and mildew infection would have occurred with dry weather April 9-10 and 13-14, so we should now be spraying apples for scab, the rusts and mildew.

After-infection control of rusts: Quince rust and cedar-apple rust spores were released and likely found a susceptible target in apple blossoms at open cluster.  It is best to include an SI fungicide for after-infection control of rusts, especially quince rust, considering yesterday’s warm infection period. If an EBDC fungicide had been applied just before the rain, it may have weathered through with less than an inch of rain, but where rainfall was more an inch or the most recent fungicide application was more than a week earlier, applied more than a week ago, it is best to follow-up with a supplemental SI fungicide for after-infection control of rusts.

Fire blight?: The warm temperatures over the weekend to Apr 15 might have favored fire blight Apr 14-15 if bloom opened April 11-13, but fire blight infection was not likely where bloom first opened during the day April 14 or 15. Now it looks like it will remain relatively cool into next week, but with warmer temperatures and more bloom expected by the middle of next week. Of course the fire blight threat can change quickly if the temperatures are warmer than predicted.

TYRO, VA: Similar apple disease scenarios were expected for central Virginia, where the bud stage is more advanced with bloom open last week, temperatures generally several degrees warmer and rainfall reported to be as much as 2.4 inch.

Sunday, April 13, 2014

Scab infection at Winchester Apr 11-12

At our AREC near Winchester, wetting which began at 6 PM Apr 11 and continued for 14 hours at 64-40° F was long enough for a scab infection period. Total rainfall during the infection period was only 0.01 inch.


Wetting during this event was not long enough for scab infection at Tyro, Apr 11-12.

Tuesday, April 8, 2014

Wetting April 7-8 Winchester and Tyro, VA

Apple buds at our AREC are now at 1/2-inch green-tip stage with some approaching tight cluster. 

With wetting starting at 6 AM yesterday, and starting to dry as of 8 AM this morning, we did not have enough wetting for a scab infection at 38-44° F.

Wetting in the Tyro area, central Virginia, began at 4 AM Apr 7 and continued for more than 26 hours at 42-47° F with 1.25 inch rain. This was more than adequate for a scab infection period. Tyro also was close to an infection period  Apr 3-4 with 11 hr wet with light rain and temperatures 51-59° F.

Expect the release of powdery mildew conidia as buds approach the tight cluster stage.

Monday, March 31, 2014

At last, it's a new season!



On Monday, March 31, we saw our first green-tip stage showing on Gala (above) and Red Delicious apples, and that raises the question whether wetting March 29-30 was enough for a scab infection period. 

At our AREC, we had just enough wetting (18 hr wet at 48-40° F, with 0.54 inch of rain), and we did trap scab ascospores, but probably had very little green tissue exposed during the wetting period.

This year, we will be tracking and reporting disease update information based on data we are receiving from weather stations placed in Silver Creek Orchards, Pharsalia Road in Tyro, Nelson County, Virginia. Green tip was also reported on Pink Lady apples in that area. There was considerably more wetting in Tyro than at Winchester, easily long enough for scab infection: 26 hr wet at 57-48° F, then 3 hr dry, followed by 7 more hours wet at 34-44°, with a total of 1.72 inch of rain. There was probably enough green tissue exposed during the wetting, so the only question is whether scab ascospores were present and mature for the wetting event. Wherever there was scab present in the orchard or on nearby untended trees in fall  2013, spores were likely mature and available to infect.

Where apples are just beginning to show green-tip, it is definitely time for protective fungicides such as copper or EBDCs; however, if green tissue was exposed during this potential infection event, it would be prudent to include a fungicide with after-infection activity with the protectant if this is the first fungicide application. We have found Vangard (cyprodinil) to be compatible with copper, and effective in such situations. Because of fruit russet concerns, copper materials should not be applied to fresh market fruit after 1/4-inch green-tip stage. 

We thank Dr. Mizuho Nita, grape pathologist with Alson H. Smith AREC, Winchester, for procuring funding and placing the weather stations in Tyro. We also thank John Saunders, Silver Creek Orchards, for hosting these weather stations and helping us to install them. As the season progresses, we hope to compare accumulated wetting, temperature, and infection conditions within adjacent grape and apple leaf canopies at three elevations from approximately 944-1462 ft. Dr. Nita's funding came from a VDACS SCRI block grant (Virginia Dept. of Agriculture and Consumer Services, Specialty Crop Research Initiative).

Thursday, October 31, 2013

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.

Friday, August 30, 2013

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.

Wednesday, August 14, 2013

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!
 

Wednesday, August 7, 2013

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.
 

Tuesday, July 23, 2013

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.

Tuesday, July 16, 2013

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!



 

Tuesday, July 9, 2013

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.

Monday, July 1, 2013

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.

Monday, June 24, 2013

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.

Saturday, June 22, 2013

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.

Monday, June 17, 2013

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.

Tuesday, June 11, 2013

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. 

Monday, June 10, 2013

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

Monday, June 3, 2013

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.

Tuesday, May 28, 2013

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.

Friday, May 24, 2013

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°.

Thursday, May 23, 2013

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.

Saturday, May 18, 2013

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.