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).