Wetting hours Aug. 23-30.

There were 49 total wetting hours at our AREC last week, bringing this year's total to 514. This is the lowest total accumulated wetting hours through the end of August since we started keeping track of wetting hours in 1994. The previous low was 521 hr for 1999. Totals for other years, except 1999, since 1994 were all more than 600 hr by now, ranging from 601 in 2005 to 967 in 2000. The total by this time last year was 808 hr.

Fruit maturity

Dave Carbaugh reports that, although the cultivars Ginger Gold, Gala and Honey Crisp matured earlier than normal this year, Red Delicious and Golden Delicious are closer to normal. As of Aug. 24 there was still a lot of starch to convert- a relative rating of 1.7 for Reds and 1.4 for Goldens on a scale of 1-10 where 1 means there is a lot of starch. Soluble solids (sugar) is already on the upswing, 11.5% for Reds and 12.8 for Goldens. Firmness is still good- 18.2 lb for Reds and 18.6 for Goldens. The combination of high starch, good firmness and cooler night-time temperatures for improved fruit coloring bodes well for fresh market cultivars. So, in spite of the earlier bloom date this year, all these criteria are optimistic for a normal progression into harvest and some opportunity to wait for improved color. Last year on the same assessment date, Red Delicious firmness was 17.5 lb, soluble solids 10.2% and starch rating 1.9. Goldens in 2009 were 17.2 lb, soluble solids 12.4% and starch rating 1.7.

Extended wetting Aug 23-24

Extended wetting Aug. 23-24, 16 hr at 67º with 0.8 in. rain. (A pretty good soaker this time).

Wetting hours Aug 16-23

There were 44 total wetting hours last week, bringing this year's total to 465. A significant portion of last week's wetting hour total was from rainfall at relatively warm temperatures (as noted below), increasing the potential for rot development on maturing peach and apple fruits.

Extended wetting Aug. 18-19

Extended wetting Aug. 18-19, 26 hr at 69º with 0.46 in. rain.

Also 13 hr wetting Aug 15-16 at 76º with 0.02 in. rain.

Extended wetting and increased summer disease activity

Extended wetting Aug. 12-13, 21 hr at 73º (0.58 in. rain at our AREC). There were 64 total wetting hours last week, bringing this year's total to 421. Also extended wetting Aug. 15-16 13.5 hr at 76º (0.24 in. rain)
  Of course any rain we get is much needed, but these rains at warm temperatures do increase the potential for summer diseases, especially bitter rot.  Bitter rot has been observed on fruit which had frost cracks, potentially increasing the inoculum level and disease pressure on healthy fruit.

Increased summer disease activity

Extended wetting Aug. 4, 7.5 hr at 76º (with only 0.05 in. rain at our AREC). There were 24 total wetting hours last week, bringing this year's total to 357.
There were several other warm showers last week and a total of 0.41 in. rain. Bitter rot has been observed on fruit which had frost cracks, potentially increasing the inoculum level and disease pressure on healthy fruit.

Wetting hours last week

Extended wetting July 31-Aug. 1, 9.5 hr at 68º (but only 0.04 in. rain at our AREC). There were 20 total wetting hours last week, bringing this year's total to 333.

Wetting hours last week

Wetting hours last week: 15; total this year: 313.

Extended wetting period

Extended wetting July 13-14 (0.59 in.), with 14 hrs wetting at 71º, favored fruit rot infections. There were 22 wetting hours last week, bringing this year's total to 298. Sooty blotch and flyspeck are now visible on unprotected fruit at lower elevations at our AREC.

Extended wetting and accumulated wetting hours.

We finally got some much-needed rain July 9-10 (0.65 in.), with 12.5 hrs wetting at 73º. Wetting at this temperature favors rot infections. There were 17 wetting hours last week, bringing this year's total to 276. The total for the past three weeks was only 29 hours, the lowest 3-week total since we started recording wetting hours in 1994.

Low wetting hours, sunburn and heat injury

Accumulated wetting hours (starting April 29, 10 days after petal fall), as of July 5: Winchester AREC, 259 hr. Although we surpassed the 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit last week, accumulation of wetting hours has been very slow the past two weeks- totaling only 12 hours. This is the fewest hours accumulated in a 2-week period since we started keeping track of this statistic in 1994. The next closest to this was in 1998 when 14 wetting hours accumulated from Aug. 24- Sept. 6. That year a 3-week period totalled only 36 hours. We have had no extended wetting periods since June 15. In spite of the lack of rainfall, apple fruit size hasn't suffered much yet, but we really could use a good soaking rain.

Heat injury: We have seen an increase in the amount of sunburn and heat injury on apple fruit, as would be expected with the warm temperatures and exposure of fruit to the sun with increasing crop load. The examples of York Imperial fruit shown above were brought to the lab from a commercial orchard today. Internal browning of the flesh correlated with surface discoloration on the more exposed side of the fruit. A cross section through the core showed that the seeds were white and healthy looking, indicating that the surface symptoms were not due to frost injury, and there was no evidence of fungal growth as would be present in a pathogenic condition such as moldy core. Typically, the heat-injured side of the fruit will stop growing while the non-injured side continues to grow, resulting in a disfigured fruit.

Sooty blotch and flyspeck

Sooty blotch and flyspeck were observed in a commercial orchard in Nelson county yesterday, July 1. The pinkish area may indicate early rot infection. I do not have recorded wetting hours for this location.

Wetting hours for sooty blotch and flyspeck

Above is a wild blackberry cane with sooty blotch and flyspeck colonies-a common inoculum source for primary infection of apple fruit. Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19), as of June 28: Winchester AREC, 252 hr. Accumulation of wetting hours has been slow the past week, but we have just reached the 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit. We have had no extended wetting periods since June 15. Washington, VA in Rappahannock county has had more wetting hours, with a total of 338 as of June 28. Hit-or-miss evening showers likely led to some of the difference in accumulated hours and would also make a difference in areas of Frederick county that received evening wetting in the past two weeks.

Sooty blotch / flyspeck wetting hour threshold

As of yesterday morning, June 21, we had 247 accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19). This is very near the 250-hour threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit.

Infection period for scab and summer diseases

June 14-15: Wet 12 hr at mean 73º- favorable for warm weather summer diseases such as bitter rot.

Wetting hours for summer diseases

Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19): 218 hr. The wetting hour threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit is 250 hr. It is expected that we will reach that threshold in the next week. Update: Rappahannock county (Washington, VA) has surpassed the 250-hr threshold, with 282 wetting hours as of June 16.

June 9: Apple scab infection period; wet 11 hr at mean 61º.

This is a reminder of the breakfast meeting at our AREC Thursday, June 17 at 7 AM. The main purpose of this meeting is to further assess weather-related crop losses to tree fruit in our counties and the submission of a crop damage assessment to the state government. Bill Whittle will lead this assessment at the meeting on Thursday, with the intention of collecting updated information on crop damage that may be used to trigger some remedial actions at the state level. We encourage you to provide feedback regarding your crop loss situation. In addition to addressing this topic, Plant Pathology and Entomology updates will be given during breakfast.

Mildew days and wetting hours

As an indicator of relative annual mildew pressure, we note the number of days above 53º without rain as potential "mildew days". From March 30, when powdery mildew spores were first were available on infected emerging buds, until June 1, we had 45 mildew days this year. Since 1993, the number of such days from tight cluster to six weeks after petal fall (about third cover) has ranged from 24 (in '96 and '03) to 49 in '99. This year ranks as the second most frequent mildew weather in 18 years.

Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19) now stand at 185 hr. The wetting hour threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit is 250 hr. Rappahannock county (Washington, VA) has logged 237 wetting hours, also as of June 7, using the Apr 19 petal fall and Apr 29 start accumulation date. Rappahannock's total will be updated every two weeks.

Cherry rots

Sweet cherries are now ripe, or nearly so. The fruit on the right looks good; the one on the left not so good. Rains such as we had yesterday lead to cracking of ripening fruit and increased susceptibility to rots. The fruit above left is a good example of two common rot fungi- the tan colored sporulation on the right side, characteristic of brown rot and the dark green sporulation of Alternaria rot in the center. The grayish area to the left side is probably a mixture of both of these fungi growing together. A pre-harvest application of a sterol-inhibiting fungicide such as fenbuconazole (Indar) should give excellent control of brown rot but will be weak on Alternaria unless it is supplemented with something with a broader spectrum of activity such as captan. Pristine (a mixture of pyraclostrobin and boscalid) should be excellent for control of both Alternaria and brown rot.

Brown rot pressure is often influenced by warm, rainy weather during the period immediately before harvest. Because cherries are the first stone fruit to ripen, a brown rot problem there may signal a potential inoculum source and problem to follow on adjacent stone fruits which ripen later, including peaches, plums, nectarines and apricots.

Summer disease outlook

Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19): 165 hr. The threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit is 250 hr. As of May 25 a hygrothermograph in Rappahannock county (Washington, VA) had logged 163 wetting hours, also using the Apr 19 petal fall and Apr 29 start accumulation date.

For practical purposes, cedar-apple rust galls near our AREC have completed their sporulation for this year. Rust lesions are still showing up on apple leaves that were not protected two weeks ago.

Scab and rust infection periods

May 23-24: Apple scab and cedar-apple rust infection period; wet 14 hr at mean 65º.

May 22-23: Apple scab and cedar-apple rust infection period; wet 17 hr at mean 65º with 0.09 in. rain.

Reminder: Breakfast meeting May 20

There will be a breakfast meeting at our AREC at 7 AM tomorrow, May 20. In addition to the usual insect and disease management updates, there will be comments about this year's apple thinning tests by David Carbaugh. Also, Bill Whittle, area Farm Business Management Agent, will discuss a possible crop survey.

Scab and cedar rust infection

Apple scab and cedar-apple rust infection period May 17-18. Wet more than 26 hr at 58-49º with 1.1 in. rain.

Scab and cedar-apple rust infection period

May 12-13; wet 19 hr at 51-66º with 0.09 in. rain. Another apple scab and cedar-apple rust infection period.

Scab and rust infection period

May 11-12; wet 17 hr at 46-54º with 0.32 in. rain. An apple scab and cedar-apple rust infection period.

Early season apple disease summary

Apple scab:
Scab ascospores were first trapped with rains March 22.
First primary scab infection period: Mar 28-29 (20 hr at 42-44º mean with 1.62 in. rain);
Scab lesions were observed on Golden Delicious Apr 12.
Primary or secondary scab infection periods:
Apr 13-14 (wet 22 hours at 44º with 0.07 inches of rain); Consider this likely to be an early secondary infection period where lesions were sporulating if 1/2" greentip-tight cluster growth was not protected for the Mar 28-29 infection period. This wetting period was too cold for rust infection.
Apr 25-27 (intermittent wetting approximately 28 hr at 53-63º with 1.3-in. rain total for event).
May 2-3 (11 hr at 72º with 0.4 in. rain).
All overwintering ascospores should be discharged by now, but it is important now to be sure that there are not lesions in the tree which would indicate potential for secondary infection of fruit.

Rusts:
Cedar-apple rust infection periods Apr 25-27 (28 hr at 53-63º with 1.3-in. rain total for event) and May 2-3 (11 hr at 72º with 0.4 in. rain); infection is not yet visible from either of these infection periods. Quince rust infection this year not too likely because most fruit would have become resistant by the time they reached thinning size and warmer wetting periods occurred.
Much cedar-apple rust inoculum remains to be discharged and inoculum may persist late into spring as it did several years ago. Heavy cedar rust infection can reduce return bloom. If the orchard is in a rust-prone location and residual protection is in doubt, it is best to supplement the next application with an SI fungicide for after-infection rust control.

Powdery mildew:
Mildew has been our most active disease this year. Spores were available on infected emerging buds by Mar 30.
Infection pressure has been almost ongoing with 29 dry weather “mildew days” since Mar 30.

Fire Blight:
Earliest bloom open at our AREC on Idareds Apr 5.
Infection events occurred at our AREC Apr 8 and Apr 16 (some local areas may also have had wetting of early bloom Apr 6). Blossom blight symptoms were predicted to start appearing Apr 30 from Apr 8 and May 2 from Apr 16. (Blossom blight symptoms have been reported from Frederick County). Canker blight symptoms were predicted for May 1, and trauma blight symptoms were predicted to appear May 4 from blight due to hail damage Apr 25. Temperatures favored infection with wetting where late bloom was still Apr 30-May 5. Wetting from a spray application is adequate for infection on an otherwise dry day.

Meeting reminder- 6 PM May 6

This is a meeting reminder for our second In-depth evening meeting, May 6. The focus will be on weed identification and management with Dr. Jeff Derr, Hampton Roads AREC. Note that we will start at an earlier time than usual (6 PM) for a weed identification field tour, followed by disease and insect management updates and an in-depth presentation by Dr. Derr on weed management.

Scab and rust infection period

A scab and rust infection period ended Monday morning, May 3: 11 hr, 72 deg., 0.4 in. rain. Heavy secondary/primary apple scab from the April 14 infection period is now evident on unprotected shoot leaves. Consider options for stronger "catch-up" treatments if your orchard was not properly covered for the earlier infection periods March 28 and Apr 14 or the more recent ones which could result in damaging secondary fruit infection, Apr 24-25, Apr 25-27, and May 2-3.

Secondary mildew infection is also apparent from ongoing infections which occurred on at least 21 days in April.

Apple Blossom Festival weekend temperatures were actually slightly warmer than those indicated as predicted below, resulting in possible fire blight infection on late bloom wherever wetting occurred. The warmer temperatures should also bring earlier than predicted blossom blight symptom development this week.

For purposes of monitoring cumulative wetting hours for sooty blotch and flyspeck development, we are using Apr 19 as petal fall and wetting hour accumulation of wetting hours begins 10 days later, Apr 29. So far we have accumulated 11 hours toward the 250-hr threshold. 

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.


FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With most apple trees at or beyond petal fall but others with susceptible bloom that will likely persist through the weekend, here is a prediction for areas where bloom was first open Apr 5, 2010. The temperature and wetting data are current through Thursday morning, Apr 29. Predicted weather conditions are shown for Apr 29-May 2. 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 infection could have occurred Apr 16 and Apr 8 (not shown). With the return of warm weather for Festival Weekend, risk will again increase to an infective level if there is any wetting of susceptible late bloom tomorrow and into next week. “Wetting” can occur with a thinning or maintenance spray and inclusion of streptomycin with such sprays is advised. Wetting and infection can also occur with heavy dew. BBS column, tracking the Apr 8 and Apr 16 infections, shows that the blossom blight symptoms from these two infections will begin to appear Apr 30-May 2. (Blossom blight was observed yesterday in Rappahannock County). Canker blight symptoms (CBS), resulting from the extension of overwintering cankers to involve new growth will also appear in the next few days. Continue to protect high-risk blocks through late bloom as needed. 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

A heavy scab and rust infection period ended last night; variable and intermitent wetting approximately 28 hr at 53-63 degrees with 1.3-in. rain total for the event Apr 25-27.  (Actually our wetness sensor was wetted and dried 11 times yesterday!). Fruit that are big enough to thin now were probably no longer susceptible to quince rust, but smaller fruit of later blooming cultivars such as Yorks and Romes are still susceptible.  It is likely that a protectant fungicide would not have weathered through the recent wettting period. If your orchard is in a rust-prone location, the safest bet would be to supplement the next application with an SI fungicide for after-infection rust control.

Several calls have been received related to fire blight symptoms in areas east of the Blue Ridge, evidence of early season infection which probably occurred Apr 6 or earlier.

Monday 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.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With some apple trees at petal fall but others such as York, Rome and Nittany with much susceptible bloom, here is a prediction for areas where bloom was first open Apr 5, 2010. The temperature and rainfall data are current through Monday 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). The risk column shows that infection could have occurred Apr 16 and Apr 8 (not shown). Risk is currently reduced through Apr 28 but will increase where late bloom persists to Apr 30. BBS column, tracking the Apr 8 infection, shows that using extended predicted temperatures, the earliest blossom blight symptoms would begin to appear Apr 29. With the past weekend's recorded temperatures, inserting hail injury into the Maryblyt model for yesterday indicates that infection could have yesterday and an immediate streptomycin application would be suggested for such areas. As always, be aware that risks can increase quickly with warmer than predicted temperatures and unpredicted wetting, and protect high-risk blocks through late bloom as needed. 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.

Other diseases:
A scab and rust infection period in progress. Cedar-apple rust gall spore horns are fully extended. There is a surprising amount of bloom remaining, especially on York, Rome Beauty and Nittany cultivars. These blossoms are probably susceptible to quince rust as well as fire blight.

Maryblyt 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.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With some apple trees at petal fall but many still with susceptible bloom, here is a prediction for trees with first bloom open Monday, Apr 5, 2010. The temperature and rainfall data are current through Friday morning, Apr 23. Predicted weather conditions are shown for Apr 23-26. 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). The risk column shows that infection could have occurred Apr 16 and Apr 8 (not shown). Risk is reduced through at least Apr 26 as shown, due to cool weather (and actually well into next week with the current forecast). As always, be aware that risks can increase quickly with warmer than predicted temperatures and unpredicted wetting, and protect high-risk blocks through late bloom as needed. BBS column, now tracking the Apr 8 infection, the infection shows that we will have reached 91% of the requirement for predicted blossom blight symptoms by Apr 26; using extended predicted temperatures the BBS column would predict the earliest blossom blight symptoms Apr 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.

Summary of apple disease conditions to date

Scab
Scab spores were first trapped with rains March 22.
The first scab infection period occurred Mar 28-29.
Lesions were observed Apr 12.
Apr 14- apple scab infection period; wet 22 hours with 0.1 inches of rain.

Powdery mildew
Mildew spores were available on infected emerging buds by Mar 30.
There have already been 17 dry weather “mildew days” in April

Fire blight
Infection events occurred at our AREC Apr 8 and Apr 16 (some local areas may also have had wetting of early bloom Apr 6).
Possible infection yet on late bloom with warmer temperatures this weekend.

Rusts
Not much rust activity so far. 
Cedar-apple rust spores ready to be discharged.
Quince rust infection not likely as fruit will lose susceptibility by thinning time.
Cedar-apple rust inoculum may persist late into spring as it did several years ago.

Disease 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.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With some apple trees at petal fall but many still with much susceptible bloom, here is a prediction for trees with first bloom open Monday, Apr 5. The temperature and rainfall data are current through Monday morning, Apr 19. Predicted weather conditions are shown for Apr 19-22. 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). The risk column show that infection was possible as predicted Friday. BBS column shows that we have only reached 55% of the requirement for predicted blossom blight symptoms tracked from the Apr 8 infection. Risk is reduced through Apr 22, as shown, due to cool weather (and actually on into next week with the current extended forecast). As always, be aware that risks can increase quickly with warmer than predicted temperatures and unpredicted wetting, and protect high-risk blocks through late bloom as needed. 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.
OTHER DISEASES: Very intermittent wetting totaling only 0.02 inches of rain Apr 16-17 probably did not result in apple scab or rust infection, especially where protectants against these diseases were applied last week. If you are in a quince rust-prone area and did not have adequate rust protection, it may be wise to include an SI (sterol-inhibiting) fungicide for after-infection rust control in your next application. 
Meanwhile, all of these dry days continue to favor secondary powdery mildew infection.

Fire blight caution

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 most apple orchards still near full bloom, here is a prediction for trees with first bloom open Monday, Apr 5, 2010. The temperature and rainfall data are current through Friday evening, Apr 16. Predicted weather conditions are shown for Apr 16-19. 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 wetting today would result in predicted fire blight infection. For infection to be predicted, wetting (from rain, heavy dew, or a spray application) has to occur when the EIP (epiphytic infection potential) reaches 100 or higher. With cooler predicted temperatures tomorrow, the risk should again decline well into next week. However, be aware that risks can increase quickly with warmer than predicted temperatures and unpredicted wetting. Growers are advised to be alert to changes in forecasts on a day to day basis and protect high-risk blocks through late bloom as needed. The Maryblyt graphic will be updated Apr 19. 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.

Friday morning update

Based on today's forecast, it appears that this afternoon's wetting will result in predicted fire blight infection, as shown below, and continued wetting through the night will constitute apple scab, quince rust and cedar-apple rust infection periods with winds primarily WNW from cedar inoculum sources. This will be updated with a Maryblyt graphic later this morning. With most area orchards still near full bloom, flowers are highly susceptible to fire blight and quince rust. Winds will not be favorable for spraying tomorrow so protection of high priority blocks is important. Also, consider this a secondary scab infection period for orchards that were not properly protected for the Mar 28-29 infection period.

Dr. Rongcai Yuan

Sadly I report the passing of our friend, horticulturist Dr. Rongcai Yuan, April 14. Please see this link for his obituary.

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.


FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With most apple orchards still near full bloom, here is a prediction for trees with first bloom open Monday, Apr 5, 2010. The temperature and rainfall data are current through Wednesday evening, Apr 14. Predicted weather conditions are shown for Apr 15-19. 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 occurred with wind-driven rains as predicted Apr 8. For infection to be predicted, wetting has to occur when the EIP (epiphytic infection potential) reaches 100 or higher. Currently, the fire blight threat has been reduced by cooler temperatures, but the risk will again increase with warmer temperatures then next two days and possible showers Friday, Apr 16. Based on cooler predicted temperatures, the risk should again subside through the weekend. Be aware that risks can increase quickly with warmer than predicted temperatures and unpredicted wetting. The Maryblyt graphic will be updated Apr 16. 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

We recorded an apple scab infection period from 10 AM Apr 13- 8 AM Apr 14; wet 22 hours with 0.1 inches of rain. Few quince rust or cedar-apple rust spores have been discharged, so it is not likely that rust infection occurred although blossoms would still be very susceptible to quince rust infection. Hopefully, protectant fungicides applied last week would have lasted through this wetting event with only 0.1 inch of rain. If an orchard was not adequately protected, a fungicide with after-infection activity is advised.

Scab lesions sporulating

Today we observed apple scab lesions already producing conidia (above). This lesion appeared on the underside mid-rib of a non-protected Golden Delicious leaf, likely from the infection period March 28-29 (click on "older posts" link at the bottom of the page). Finding lesions now has important implications for possible secondary infection with showers tomorrow. As indicated below, fire blight infection should not occur with the cool temperature but it could be warm enough for cedar-apple rust and quince rust, depending on the length of wetting by showers.

It is quite unusual for scab lesions to appear in just 14 days from the first infection period. I recall this happening only one other time in my 34 years at Winchester. But averaging daily high and low temperatures during this 14-day period gives a mean of about 60 degrees F. At this temperature the incubation period would be about 11 days (see Mills Table, page 88 in the 2010 Spray Bulletin). But the straight numerical average of highs and lows is too high because it doesn't take into consideration that the growth of the fungus would have been inhibited by temperatures above 82 F which occurred four days during the incubation period. This finding does show that the scab fungus is able to survive the 93 F which was recorded Apr 7 in a sheltered weather station 20 ft. from where the lesion was located.

Fire blight outlook

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 most apple orchards near full bloom, here is a prediction for trees with first bloom open Monday, Apr 5, 2010. The temperature and rainfall data are current through Monday morning, Apr 12. Predicted weather conditions are shown for Apr 12-16. 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 occurred as predicted earlier with storms Apr 8. The wind-driven rains made it likely that bacteria would have spread throughout an orchard from blossoms that were open earlier to ones that had opened just before the rain. For infection to be predicted, wetting has to occur when the EIP (epiphytic infection potential) reaches 100 or higher, and this level had reached 4X that threshold Apr 7. Currently, cooler temperatures are expected to reduce the fire blight threat through Apr 14, but the risk will again increase with warmer temperatures Apr 15-16 and possible showers Apr 16. Be aware that risks can increase quickly with warmer temperatures and unpredicted wetting. The Maryblyt graphic will be updated Apr 14 or sooner. 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 situation

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 most cultivars near full bloom and all with some bloom open, here is a prediction for trees with first bloom open Monday, April 5, 2010. The temperature and rainfall data are current through Friday morning, April 9. Predicted weather conditions are shown for April 9-12. 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 occurred as predicted with storms with strong winds yesterday afternoon. The wind-driven rains made it likely that bacteria would have spread throughout an orchard from blossoms that were open earlier to ones that had opened just before the rain. For infection to be predicted, wetting has to occur after the EIP (epiphytic infection potential) reaches 100 or higher, and this level had reached 4X that threshold.  Cooler temperatures will reduce the fire blight threat through the weekend. The Maryblyt graphic will be updated April 12 or earlier if it changes dramatically. 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.

Other diseases:
Yesterday's 10-hr wetting from 4 PM to 2 AM this morning was not quite long for apple scab infection, and cedar-apple rust spores were not released. Predicted dry weather through most of next week will again favor powdery mildew infection.

Maryblyt prediction for today

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: Here is a cropped graphic from the Maryblyt 7 program. With early cultivars near full bloom and nearly all with some bloom now open, here is a prediction for trees with first bloom open Monday, April 5, 2010. The temperature and rainfall data are current through Thursday morning, April 8. Predicted weather conditions are shown for April 8-12. 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 is possible with predicted thunderstorms this afternoon and evening. For infection to be predicted, wetting has to occur after the EIP (epiphytic infection potential) reaches 100 or higher. Note that this level has reached more than 4X that threshold. Any unprotected block that had blossoms open yesterday is at risk for infection if wetting occurs today. The current longer-range outlook indicates cooler temperatures April 9-10, followed by warming again April 11-12. 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 other diseases

The fire blight outlook for today remains essentially as shown yesterday. Unprotected orchard blocks with bloom open yesterday are at risk for fire blight infection if wetting occurs with storms today.

Depending on when wetting occurs and how long it stays wet, it may also result in another scab infection period and our first cedar-apple and quince rust infection period of the year.

Fire Blight Situation at Winchester VA

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 showing much bloom, and others expected to come into bloom with warm temperatures today, here is a prediction for trees with first bloom open Monday, April 5, 2010. The temperature and rainfall data are current through Wednesday morning, April 7. Predicted weather conditions are shown for April 7-11. 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 (I) is possible with predicted thunderstorms tomorrow, April 8 (note red color). For infection to be predicted, wetting has to occur after the EIP (epiphytic infection potential) reaches 100 or higher. Briefly put, any bloom that opens today is at risk for infection if wetting occurs tomorrow. The current longer-range outlook indicates cool temperatures April 9-10, followed by warmer again April 11-12. This graphic will be updated April 8. The BBS and CBS columns are tracking predicted blossom blight symptom and canker blight symptom appearance, respectively. 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.

Early fire blight threat

Warm temperatures the past several days have brought rapid bud advancement. Where the first blossom opens any day from April 5-7, MARYBLYT predicts a possibility of fire blight blossom infection if showers or other wetting occurs on Thursday, April 8. At right, Idared king bloom open at 9 AM April 6.

Mildew weather continues

Idareds and Red Delicious are now at open cluster to early pink stage, and rapid bud development is expected with temperatures reaching the high 70s and 80s the next four days.

Currently there is no rain showing in the 10-day forecast which means that each of these days will be a mildew infection day. With rapid bud development there will be a lot of unprotected tissue exposed, including blossoms for fruit infection and the resulting mildew russet pictured in the post below.

Mildew can have a serious economic impact on  yield and fruit quality of susceptible cultivars and it is generally beneficial to keep a tighter spray schedule regardless of which class of mildew fungicide (SI, strobilurin, sulfur) you choose. If you had a mildew problem last year, this is the time of the year to get on top of it. Note that EBDCs (mancozeb, Polyram), captan, dodine, copper, and AP (Vangard, Scala) fungicides do not add anything for mildew control.

Another mildew year??

In spite of the early scab infection period, it is starting out as a powdery mildew year. Powdery mildew is our only "dry weather" fungal apple disease.  The past 3 days and 8 of the next 10 days are predicted mildew infection days. The image above shows heavy sporulation covering an infected blossom cluster 4/2/10. The image above right shows a healthy bud on the left compared to a mildew-infected bud (right) 3/31/10. Expect secondary infection symptoms to start appearing during bloom to petal fall. Fruit infection occurs about pink stage and causes fruit russet (right).

Update 3/29/10

Apple scab:

Bud stage on different cultivars now ranges from green tip to tight cluster. Wetting from 2 PM March 28-1 PM March 29 resulted in our first scab infection. Assuming that few orchards have had any protectant fungicide (copper, EBDC, etc.) applied before the recent rains, it is advised that a fungicide mixture including some back action on scab be applied as soon as it is suitable for spraying. Where the scab fungus has become resistant to SI fungicides (Rally, Rubigan, etc.), after-infection fungicide options include a strobilurin (Flint, Sovran) or an AP (Vangard, Scala) and these should be combined with an EBDC (mancozeb). For processing varieties, where there is less concern about fruit russet problems, there may be interest in applying copper as a protectant for fire blight and scab. We have tested the tank-mix combination of Vangard + copper and found that it is suitable to add Vangard to copper for post-infection control of scab. Be aware that copper does not give post-infection control of scab, and the Vangard + copper tank-mix will not control rusts or mildew.

Apple powdery mildew:

Predicted warm and dry weather later this week will bring rapid bud advancement and early secondary powdery mildew infection of leaves and blossoms.  The image at the right shows chains of  powdery mildew conidia emerging from an infected Idared flower sepal 3/31/10.

Rusts:
Check the rust gall inoculum in your area; cedar-apple rust and quince rust spores will likely be released with the next warm rain.

It's a new season!

Apples:
Late winter snow cover aided overwintering of apple scab ascospores. We had green tip showing on Idared apples by March 19. Scab spores were first trapped with rains last Monday morning, March 22. By our AREC records, the extended wetting from 8 PM March 25 to 11 AM March 26 was not quite long enough for scab infection, but showers in the area were variable and one more hour’s wetting would have resulted in a scab infection period.

Peaches:
Peach leaf curl spores overwinter all over the surface of the tree and, if not controlled by a dormant fungicide, typically infect with the wetting periods soon after bud swell. This would have occurred with rains March 25-26.