Another, probably less devastating, frost event is expected tomorrow, April 18

Posted on April 17, 2022 by S. Sherif

Another frost/freeze event is expected from midnight today to 9:00 am tomorrow (Monday, April 18), with temp as low as 30 ^oF in some portions of central, northern, and northwest Virginia. On their webpage, the National Weather Service stated that “this frost and freeze conditions will kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing”. I can’t comment about plumbing, but I can probably provide insights into how this frost event would impact apples, peaches, and apples in the state. In our location in Winchester, VA, most apple cultivars, including Honeycrisp, Gala, Fuji, Reds, and Goldens, are between 20%- 90% bloom. Some early cultivars, e.g., Pink Lady and Zestar, are already post-bloom. For cultivars at early bloom and full bloom, 10% kill happens at temperatures below 28 ^oF for > 30 min; and 90% kill happens if the temp drops below 25 ^oF for >30 min. Based on the current forecast, the lowest temp in most of the locations I looked at in Frederick, Rappahannock/Maddison, Roanoke, Nelson, and Carroll counties, is 30 ^oF, which should not, theoretically, cause any significant damage to apple blossoms. For cultivars at post-bloom and petal fall, subfreezing temp (below 32 ^oF) can cause damage to the skin of developing fruitlets, leading to “frost rings”. Fruits with a frost ring will likely grow normally until harvest, but blossoms damaged by the frost will likely abscise within the next 2-4 weeks. Temperatures above 28 ^oF should not cause significant damage to flowers and developing fruits of peaches and sweet cherries.

Early season applications to improve fruit size and control bitter pit in apple.

Posted on April 11, 2022 by S. Sherif

Prohexadione calcium to reduce bitter pit incidence:

– Shoot growth reduction by prohexadione calcium (PC) early in the season (at Pink) can significantly reduce bitter pit incidence in ‘Honeycrisp’ apples.

– PC applications at pink also reduce the incidence of shoot/fire blight.

Use at the rate of 6 oz/acre.
- PC should not be mixed with calcium or boron.
- Adding a non-ionic surfactant (e.g., Regulaid or LI700) to the tank increases the efficiency of PC applications.
- If the water source contains high levels of calcium carbonate (hard water), add spray-grad ammonium sulfate (AMS) to the spray tank at a rate of (1 lb AMS to 1 lb PC) or according to the product label.
- Don’t spray if rain is expected within 8h of application.
- Both Kudos and Apogee are PC products labeled for use at the pink stage.

Calcium applications:

– Between 15-50 lb of calcium chloride (CaCl2) should be added per acre per year to reduce bitter pit incidence. In other words, 2-8 pound/cover spray.

Early season applications of calcium (starting @Pink) are more critical than late-season applications.
- Foliar applications of Ca nitrate are not recommended for Delicious and York. They might cause cork-spot-like symptoms.
- Avoid CaCl₂ applications at temperatures above 75 ^oF or under slow drying conditions (e.g., early morning) as this might cause damage to the foliage, especially in sensitive apple cultivars (e.g., Idared and Golden Delicious).
- Soil applications of Ca are not efficient.
- Boron deficiency may reduce Ca movement in the tree.

Boron applications:

– Boron is an essential element for flower development and fruit set, and boron deficiency can negatively affect yield and fruit size.

– Boron is also crucial for Ca movement, and Boron deficiency may lead to Ca-deficiency disorders, including bitter pit.

Maintenance rate: 0.5-1 lb of Boron/acre (2.5 – 5 lb of Solubor/acre)
- Apply at Pink stage, tank mixed with calcium chloride.
  - OR, 7-10 after petal fall; or with the first cover spray.
- Research at WA state showed a significant positive relationship between splitting in Gala and fruit boron content. So, it is recommended to use the lowest rate of boron with Gala.

Urea applications:

Foliar applications of urea at bloom (3 lb/100 gal) and at petal fall and early cover sprays (5-6 lb/100 gal) can promote cell division, especially for Gala. These applications are particularly important when king blooms, which usually give the largest fruit, are lost to frost.

Freeze Injury Updates (Winchester-March 29): Sweet cherry blooms lost to freezing temperatures; apples and peaches made it through.

Posted on March 29, 2022 by S. Sherif

Temperature profile of orchard blocks in the AHS Jr. AREC’s research farm (Winchester, VA) on March 28-29, 2022.

Our digital temperature data loggers recorded temperatures as low as 17 oF that continued for > 2h this morning (Tuesday, March 29). Some of our apple cultivars, including Gala and Pink Lady, were at the tight cluster and first pink; whereas, others like Fuji and Honeycrisp were between half-inch green and tight cluster. Temperatures below 21F were enough to wipe out the flowers of these cultivars completely, but we were pleasantly surprised to find out that all apple cultivars we assessed this afternoon survived this frost event with minimal damage. We recorded between 15 – 35% bud mortality in the king blooms and less than 15% in the side-blooms of Honeycrisp, Gala, and Pink Lady, with the latest showing the highest percentage of damage. Similarly, the four peach cultivars (Rich May, Sunhigh, Red Haven, and John Boy) we evaluated showed less than 15% flower mortality.

I generally believe that 10-30% flower mortality after frost is not a bad thing and could even be considered desirable as a natural thinning process and to ensure a good return bloom next year. It is generally evident that thinning during bloom has a very positive impact on return bloom; and whether this thinning is done chemically (e.g. liquid lime sulfur), mechanically (e.g. hand thinning), or by mother nature, the impact on return bloom will probably be the same.

On the other hand, our sweet cherry cultivars failed to sustain these low temperatures, and despite being still in the tight-cluster stage, they were severely damaged, with an average bud mortality rate of around 80% in Ebony Pearl and Selah. Regina, a relatively late-blooming cultivar, was still at the swollen bud stage, showing 0% damage.

It is also worth noting that flower development can vary among cultivars, species, and locations in the state. Also, temperatures recorded this morning in Winchester were seriously low, but they might not be the lowest in other areas. So, you can depend on this report only if your trees are in the same developmental stage and your temperature didn’t go below 17 oF this morning. If otherwise, I suggest that you evaluate the damage in your block as per the method and images I shared in previous posts.

Flower buds were collected from three apple cultivars (Pink Lady, Gala and Honeycrisp) and assessed for damage after the frost event that occurred on the morning of March 29, 2022 in Winchester/Frederick county area.

Flowers were collected from four peach cultivars (Sun High, Rich May, John Boy and Red Haven) and assessed for damage after the frost event that occurred on the morning of March 29, 2022 in Winchester/Frederick county area.

Flowers were collected from three sweet cherry cultivars (Ebony Pearl, Regina and Selah) and assessed for damage after the frost event that occurred on the morning of March 29, 2022 in Winchester/Frederick county area.

Hard Freeze is Expected This Tuesday (March 29)

Posted on March 27, 2022 by S. Sherif

Based on the weather forecast for Tuesday, March 29, temperatures will drop to 19 ^oF for a couple of hours (6:00 – 8:00 am) in the Frederick County and Rappahannock-Madison area, which could be devastating for the majority of apple cultivars and some early-bloom peach cultivars grown in these locations. Our apple cultivars in Winchester are currently in the tight-cluster stage, and some (e.g. Pink Lady and Zestar) are in the full pink-stage now. The majority of peach cultivars are in the pink stage now, with some early-blooming cultivars (e.g. John Boy) are already in bloom. Sweet cherries, on the other hand, are still in tight-cluster stage. Based on the critical temperature tables below, 90% of apple buds at tight-cluster can be killed if exposed to temperatures at 21^oF and below for more than 30 min. Similarly, peach flowers at full bloom can be killed at the temperatures forecasted for Tuesday. Sweet cherry cultivars that are still in tight cluster will be likely OK, and only 10% can be damaged by this freeze event.

This is a typical advective freeze, accompanied by wind > 5 mph and dry air. Unfortunately, none of our frost mitigation measures, e.g., wind machines, overhead and under-tree sprinklers, can be of utility with this type of frost. Using any sprinklers, or spraying the tree with water using an air-blast or any other sprayer, will cause more damage than benefit. Heaters, on the other hand, can provide some protection if used for several hours, probably starting from midnight.

Tree fruit growers in the Nelson County may also face a brief, less damaging frost event, with the lowest temperature predicted to reach 24 ^oF before sunrise. Based on the current forecast, no frost/freeze is predicted for Roanoke and Carroll-Patrick counties.

Accede: a new chemical thinning material for apples and peaches

Posted on March 20, 2022 by S. Sherif

Accede is a new thinning product from Valent BioSciences that you may need to consider for apple fruit thinning and peach blossom thinning. The active ingredient of this product is ACC (1-aminocyclopropanecarboxylic acid (ACC); a chemical that is produced naturally in plant as a precursor for ethylene (the ripening hormone). Unlike other ethylene-based products (e.g. ethephon), Accede doesn’t cause gummosis in peach and nectarine; and is not as aggressive when thinning apples.

For apple fruit thinning: Accede can be used when the king fruit’s average fruit size ranges from 8-25 mm. However, this product is mainly intended for later thinning treatments (fruit size 15-18mm) when the primary thinning materials (e.g. 6-BA and NAA) are no longer effective. This product should be applied at a 23-46 fl oz/acre rate. A reduced rate should be considered if the temp on the day of application is >90 ^oF, and the best results are achieved under slow drying conditions (e.g., early morning, at night).

For peaches and nectarines: Accede is the only labeled chemical thinning product. Unlike apple, Accede is mainly used as a bloom thinning treatment for peaches and nectarines. It should be applied between bloom and petal fall at 34-69 fl oz/acre rate. However, it was found that two applications (at 10% bloom and full-bloom), each at 34 fl oz/100 gal/acre, can achieve the best thinning results. The product works by causing early senescence to the flowers, thus preventing fertilization and fruit set of the unwanted crop. According to research conducted in MSU in 2021, two applications of Accede, reduced fruit set significantly and cut the time needed for hand-thinning in half, compared to untreated trees.

Source: Dr. Anna Wallis, Apple Production Specialist at MSU

Precautions when using Accede for peaches and nectarines:

This product should not be applied to stressed, unhealthy trees as it may cause over-thinning. If frost occurs during bloom, you should wait until assessing the percentage of frost damage before applying Accede. The product should not be applied if rain is expected within 8h of application. Finally, this product should not be used for peaches and nectarines after petal fall.

Here is a link for the product label for more information about Accede.

https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/AccedeTM_Plant_Growth_Regulator_Label.pdf

2021 Tree Fruit Extension Survey

Posted on October 8, 2021 by S. Sherif

Greeting,

The following is a link for a very brief survey that should take less than 2 min to complete. The results of this survey will help us assess our tree-fruit research and extension program at the AHS Jr. AREC. This survey will also help us identify priority areas and extension activities most preferred by Virginia tree fruit growers and stakeholders.

Here is the survey link:

https://virginiatech.qualtrics.com/jfe/form/SV_dcZlZMMDx5SbKGa

We appreciate your help!