In any apple trees blocks still at bloom (young planted trees, and any orchards with rat tail bloom): fire blight infections have occurred on 5/3 in or around Charlottesville, Lynchburg, Wakefield and on 5/2 and 5/3 in Red Hill, and in Red Hill and Wakefield the infection will occur again tomorrow 5/4 and 5/5. Please examine attached NEWA EIP print screens. Protect by applying 1.5 lbs/A Harbour or Agri-Mycin plus Regulaid 1 pt/100 gal, before rain/dew triggering infection or up to 24 h after that rain, on any apple tees in bloom. You can still apply 5/3 for infection that occurred on 5/2. If you did not protect against the infection/s on 5/2 apply Apogee at 12 oz/100 Gal as soon as you can, best 1-3 days after infection event that you did not apply streptomycin for. Use of Apogee for and unprotected infections beyond the 24 h after infection has occurred will help you prevent fire blight cankers to develop from the currently incubating infections.
Looking at the carbohydrate thinning model and weather forecast for this week (May 2- May 9), you can realize that we, at Winchester/Fredrick county area, have only a couple of days that could be suitable for our primary fruit thinning applications. As shown in the carbohydrate model below, we are approaching the recommended degree days of 200-250 DD by this Wednesday (May 5), which would be perfect for applying our regular thinning treatments if it’s not raining that day. However, it will be apparently cold and/or rainy for the rest of the week, leaving us with only two days with temperatures above 80 oF (Sunday, May 2 and Tuesday, May 4), which is good for the activity of our main thinning materials, 6-BA and NAA. These thinners don’t work well when temperatures are below 70F. Therefore, I would recommend targeting these two days (May 2 and 4) for thinning applications. Although our current DD is slightly under the recommended range, our fruit sizes lie within the perfect range (7-13 mm) for thinning applications. In our last zoom meeting this past Wednesday, we discussed the materials and rates you can use for thinning Gala, Fuji, Honeycrisp and several other cultivars. You can access this information by following this link: https://blogs.ext.vt.edu/tree-fruit-horticulture/2021/04/20/apple-fruit-thinning-scenarios-2021/
As you can see in the model page below, the last column refers to the recommended application rate based on the 7-day carbon balance. The model suggests a standard rate of thinning material for Sunday applications and 30% increase in thinning rates for Tuesday. In other words, if your standard rate for MaxCel is (64 fl oz + 2 pt of carbaryl/acre); you need to add (83 fl oz of MaxCel + 2.6 pt of carbaryl/acre) on Tuesday. This 30% increase doesn’t apply to the surfactants you apply with the thinning mix. Please also note that some forms of 6-BA (such as Exilis 9.5) have 5X active ingredient and therefore the amounts used in the example above will be different. Similarly, for NAA there are two forms of Refine (Refine 3.5 and Refine 6.25) that contain different concentrations of ai. Please read the product label before applying any of these chemicals. Finally, feel free to approach me via the email and telephone number mentioned below.
The Apple Carbohydrate Thinning Model at NEWA.Cornell. For this location (Winchester, VA) I used March 20 and April 16 for the green tip and bloom dates, respectively. Precent flowering spurs (51-75%). The model was run on Sunday May 2nd at 2:35 am. Winchester VT AHS AREC weather station was used for this location.
Dear All: Please find below a message from Dr. Srdjan Acimovic.
In any apple trees blocks still at bloom, fire blight infection will be possible if weather forecast from NWS changes from what is now used to run EIP NEWA fire blight model: i.e. if dew or rain occurs. The currently orange labeled EIP cells with values above 100 could turn to Red color and word Infection if dew or rain occurs (attached), keep looking at model every day. Some locations (airports) I attached show that red cell change to Infection due to wetting. If this change occurs, apply 1.5 lbs/A Harbour or Agri-Mycin plus Regulaid 1 pt/100 gal, before rain/dew triggering infection or up to 24 h after that rain, on any apple or pear trees in bloom.
Please see below the updates from Dr. Srdjan Acimovic on the fire blight situation in Virginia.
If the data from Roanoke International Airport station are correct there will be fire blight infection today 4/14 triggered by the rain, in and near Roanoke. Growers should apply strep 1.5 lb + Regulaid 1 pt/100 before rain or apply this mix up to 24 h after the rain event that triggered the infection. What puzzles me is that Floyd (CLH), not so far away from Roanoke, has no infection predicted for 4/14, leading me to believe that it either one of the two stations is not calibrated properly OR it will be hit or miss in terms of where rain/dew lands. Next, the infection occurred in Esmont (Rees), Lynchburg, and Red Hill yesterday 3/13 and if the growers did not apply streptomycin before the rain/dew on 3/13 triggering the infection, they must and can still apply strep 1.5 lb + Regulaid 1 pt/100 today i.e, up to 24 h after the rain event that triggered the infection for it to be effective. In Lynchburg infection is also predicted today 4/14 and the spray today 4/14 will cover for both infections 4/13 and 4/14. In Richmond, if the station is plugging in the correct weather data into the model, there was contiguous infection 4/9-12 which is not good, and proper response as per my previous blog was to spray on 4/10, and 4/12 to cover for all 4 infections and both times growers should have applied strep 1.5 lb + Regulaid 1 pt/100 to get 24 h kick-back and thus cover for all 4 infections. This is based on my experiences from eastern NY and is different from the VA spray guidelines that currently state that a streptomycin application remains effective 3-5 days. Based on this experience with the outbreaks I saw after similar block of infection in NY, I disagree with that 3-5 days as per my blog published here: 1. Frightful Blight Model Cases How Long A Streptomycin Spray Lasts; 2. Major Scab Infection/s Possible 25-30 or 28-29 May All East NY posted on May 25, 2020. In Rustburg (Crown), I would apply strep 1.5 lb + Regulaid 1 pt/100 tomorrow 4/15 if the “High” risk turns into “Infection” for 4/14 in NEWA’s EIP model. Danville has had infections continuously from 4/8-12, assuming correct weather data. Most other weather stations do not indicate a risk from infection, assuming they are functioning properly in collecting the weather data. Please check your closest weather station in NEWA daily, and apply protection according to the EIP model, and make sure it is functioning properly before you can trust the model outputs from it.
Please find below an email I just received from our new plant pathologist, Dr. Srdjan Acimovic, regarding the fire blight situation in different Virginia locations. Dr. Srdjan will communicate his recommendations directly to you through his blog when he officially starts his job with Virginia Tech by the end of May 2021.
I am not sure are the
weather stations accurate i.e. functioning properly in the airports or
orchards, but there is a fire blight infection predicted for today and tomorrow
in Charlottesville, and there were three fire blight infections in Roanoke on
4/8, 4/9 and today 4/10, and the same is in Lynchburg. I hope the growers are
on top of looking the EIP model in NEWA daily during bloom and caught this and
already applied on 4/9 streptomycin + Regulaid in Roanoke and Lynchburg. It
they did not, I would still recommend to apply this mix today on
anything in bloom. In Charlottesville they need to apply streptomycin 17% @ 1.5
lb/A + Regulaid 1 pt/100 gal today or tomorrow (24 h after the infection
on 4/10) on anything that is in bloom. As I recommend on my talks earlier in
Feb & March, growers should look at the EIP in NEWA daily. In Manassas,
fire blight infection is predicted for 4/12, in Rustburg there is an infection
today 4/10, and there was an infection block from 4/6-8. I hope they protected
against that block. In Staunton there is an infection today 4/10, in Washington
(G cellars) there was an infection 4/7. In Newport News there is an infection
tomorrow 4/11, In Norfolk there is an infection today 4/10 and 4/11. In
Richmond infection occurred yesterday 4/9, and it still warrants an application
of strep+ Regulaid today when another infection is predicted also. In Staunton
infection is predicted today, they can spray up to 24 h after infection
today. Same spray mix recommended above will work.
Now, for all the locations that did not apply streptomycin on time in Roanoke and Lynchburg (for infection 4/8) they should immediately apply 12 oz/100 gal of Apogee or equivalent rare of Kudos, at 2-3 days from the infection on 4/8, and they should still apply streptomycin + Regulaid mix above today or tomorrow for infection today. They can mix all three, Apogee, strep, Regulaid. If no Regulaud accessible use LI700, but Regulaid is preferred.
Our digital temperature data loggers placed in four different blocks in the AHS Jr. AREC’s research farm indicated that we were hit by killing freezing temperatures in the mornings of Friday (April 2) and Saturday (April 3), with the latter being more aggressive and long-lasting. In fact, the lowest we received on Friday was 24oF, but on Saturday, our trees were hammered by temps as low as 21oF for more than 30 min. 21 oF for 30 min or more are enough to kill 90% of apple flower buds at ‘tight cluster’, ‘first pink’ and ‘full pink’. Today (April 5), we collected flower clusters from Gala, Fuji, Pink Lady, Red Delicious, Zester, and Honeycrisp. Except for Zester, all the cultivars are only moving from tight cluster to first pink. Zestar with flowers at ‘full pink’ showed 65% mortality. Other cultivars showed 45% (Fuji), 45% (Gala), 42% (Pink Lady), 15% (Red Delicious) and 5% (Honeycrisp). Unsurprisingly, king blossoms showed far more damage than side flowers. As for sweet cherries, we have recorded 93% flower mortality for flower buds at different stages (mostly first white and first bloom). Luckily and -to some extent- unexpectedly, our ‘Sunhigh’ peach flowers showed less than 25% flower despite being at the pink to the first-bloom stage. I have attached some images below to show some examples of frost damages we detected in apples and sweet cherries.
The weather forecasting predicted below freezing temperatures this past Friday (April 2nd) and this morning (Saturday, April 3rd) in the Winchester area (22602). The temperature data as it appears now on the weather network show 2h of 29 oF on Friday morning, 3h at 26 oF and 1h at 25 oF this morning. All these temperatures are above the threshold that causes 90%-kill for flower buds, but can certainly result in 10% damage for apples, sweet cherries, and peaches. To get a better idea of how much damage has occurred after the Friday frost, my research team and I collected flowers from two apple cultivars, a peach cultivar, and a cherry cultivar and evaluated flower viability after 9h of frost (around 3:00 pm, yesterday/Friday). Unfortunately, our data showed 46% and 56% mortality rate in Pink Lady apple and ‘Ebony Pearl’ sweet cherry, respectively. We observed 0% damage in the flowers of ‘Honeycrisp’ apple and ‘Sunhigh’ peach. It’s worth noting that the 46% damage observed in ‘Pink Lady’ flowers is from the King flowers only. We haven’t examined any of the side flowers because they were relatively smaller and hard to observe. It’s also important to know that ‘Pink Lady’ is at the ‘first pink’ stage now, whereas ‘Honeycrisp’, like most of our apple cultivars, are still in the ‘tight cluster’ stage. The majority of our sweet cherry and peach cultivars are at the ‘white bud’ and ‘Pink’ stage, respectively. We will examine these cultivars again tomorrow, Sunday, April 4th, to determine the final percentage of damage after the two frost events. Knowing this information is crucial before starting blossom and fruit thinning. Below are some images to show the extent of frost damage in different species.
We used a sharp razor blade to prepare longitudinal sections of sweet cherry flowers at the ‘white bud’ stage. Notice the green style and ovary tissues in the middle, as indications of flower viability. We assessed the damage for 30 flowers collected from different branches and trees. Longitudinal sections of ‘Pink Lady’ apple flowers at the ‘first pink’ stage. More than 30 king blooms were assessed for damage after 9h of a frost event that occurred on Friday, April 2, 2021 in Winchester, VA.Longitudinal sections of ‘Ebony Pearl’ sweet cherry flowers at the ‘white bud’ stage. Blossoms were assessed for damage after 9h of a frost event that occurred on Friday, April 2, 2021 in Winchester, VA.Longitudinal sections of ‘Sunhigh’ peach flowers at the ‘Pink’ stage showing alive flower styles and ovaries after a frost event that occurred on April 2nd, 2021.
DA readings refer to the level of chlorophyll (green color) in the fruit’s mesocarp, just below the skin. As the fruit ripens, chlorophyll levels decline, and so do DA readings. Starch index, fruit firmness, and, to some degree, Brix values are commonly used to determine the level of fruit maturity and harvest date for most commercial apple varieties. Generally speaking, fruits intended for CA should be picked at starch index (3-5), firmness (> 16 lb), and DA reading (around 0.60). Apples intended for fresh consumption should be harvested at starch index (5.5-7), firmness (13-16 lb), DA reading (0.35), and Brix (12-14%).
Sherif M. Sherif, Assistant Professor of Horticulture at Virginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center 595 Laurel Grove Road, Winchester, VA 22602 Tel. 540-232-6035, Email: ssherif@vt.edu
DA readings refer to the level of chlorophyll (green color) in the fruit, just below the skin. As the fruit ripens, chlorophyll levels decline, and so do DA readings. Starch index, fruit firmness, and, to some degree, Brix values are commonly used to determine the level of fruit maturity and harvest date for most commercial apple varieties. Generally speaking, fruits intended for CA should be picked at starch index (3-5), firmness (> 16 lb), and DA reading (around 0.60). Apples intended for fresh consumption should be harvested at starch index (5.5-7), firmness (13-16 lb), DA reading (0.35), and Brix (12-14%).
Sherif M. Sherif, Assistant Professor of Horticulture at Virginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center 595 Laurel Grove Road, Winchester, VA 22602 Tel. 540-232-6035, Email: ssherif@vt.edu
