Subfreezing temperatures as low as 30 oF is expected midnight tonight (Friday) to 10:00 am Saturday for northwest and western Virginia. Our cherries, peaches, and most, if not all, apple varieties are at the post-bloom stage now. The critical temperatures that can cause 10% and 90% of damage at this stage are 28 oF and 25 oF, respectively. At this stage of apple crop development, frost can cause damage to the fruits and seeds. Fruits with damaged and aborted seeds stop growing and eventually drop off. Therefore, it’s important to assess your crop first for any frost injury before starting thinning applications this coming week. You can do so by picking a few fruitless from different locations in the orchard and cut them in half by a pocket knife and observe the flesh and seed color. Damaged fruitlets will show brownish flesh and seed color. In most cases, the damage can also be observed on the fruit surface as a frost ring (See images below).
Sherif M. Sherif, Assistant Professor at Virginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center 595 Laurel Grove Road, Winchester, VA 22602 540-232-6035, Email: firstname.lastname@example.org
The average fruit size for our Gala, Pink Lady, Red Delicious, Fuji, and Honeycrisp in the Winchester area is 6.00, 6.11, 6.04, 5.72, and 6.37 mm, respectively. So, you may be wondering whether you should put any thinning application this week and if yes, when to spray and at what rate?!
The short answer is yes. You may consider applying chemical thinners, e.g. 6-BA or NAA, for your apple trees this week, preferably tomorrow, May 2nd, and Sunday (if it’s not raining). Based on the 10-d weather forecast for Winchester, it will be only Saturday and Sunday this week with temp. above 70 oF. Both 6-BA and NAA work better when the temp is greater than 65 oF. As for the rate, the carbohydrate model recommends increasing chemical thinning rate by 30%. Two things to consider here: a) Apple cultivars respond differently to thining materials. Golden Delicious, Fuji, and Cameo are usually hard-to-thin, whereas Pink Lady, Gala, Honeycrisp and Granny Smith are easier to thin. For the rates and materials recommended for Gala, Fuji, Honeycrisp, Red Delicious, Pink Lady, and Golden Delicious, use this link (https://blogs.ext.vt.edu/tree-fruit-horticulture/2020/04/02/fruit-thinning-scenarios-2020/). b) The rates mentioned on 6-BA and NAA product labels are for dilute applications (100 gal/acre). To convert from dilute to concentrate, please refer to my other post at (https://blogs.ext.vt.edu/tree-fruit-horticulture/2020/04/02/how-to-calculate-the-tree-raw-volume-trv-and-chemical-rates-for-concentrate-spraying/).
Sherif M. Sherif, Assistant Professor at Virginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center, 595 Laurel Grove Road, Winchester, VA 22602 , Email: email@example.com, Tel. 540-232-6035
Fruit size for Gala apples in the Central Virginia area is
ranging between 10-12 mm now, which is a perfect size window for post-bloom
thinning applications (e.g. by 6-BA and NAA products). Therefore, I ran the
carbohydrate thinning model on NEWA website today, April 28, to predict: a) the
tree carbohydrate level and b) thinning rates. Since 2017, we have been using
the Batesville weather station for the central Virginia area and we will keep
using the same location to help us compare among the year. We did not detect
any considerable differences in the model outputs when we used the Afton
weather station. However, if you have access to the model from your own
computer, I would recommend that you run the model yourself based on the
nearest weather station to your location. As you may be aware, any differences
in the elevation levels would change the average daily temperature which is a
critical input for calculating the tree carbohydrate level, and this will in
turn change model outputs and recommendations.
As you will see on the NEWA website, there are two
carbohydrate models, the old version which we have been using in the past three
years and the 2019 new model (Apple CHO Thinning 2019) which I will use this
year. One of the differences in the new model is the percent flowering spurs as
one of the inputs you have to add to the model. Despite the fact that Gala is
considered as an annual bearing variety and has no major issues with return
bloom, I would recommend setting the model at 50-75% flowering spurs instead of
75-100%. The reason for that is to account for the extended period of cold
weather we had during bloom and the frost damage the has been reported in some
locations. These two factors might have affected flower pollination and total
fruit set to some degree. The other two modifications in the 2019 model are: a)
the tree carbohydrate balance column in the new model is using 7-day average
values instead of 4-day average which makes it more accurate; b) the
accumulated 4 oC degree days (DD) column which predicts the number
of DD since bloom at which thinning would be highly effective. As a rule of
thumb, 200-250 DD from bloom is considered the sweetest spot for thinning
applications. Interestingly, this period often matches with the 6-12 mm fruit
size window that we have long been recommending for thinning.
With all of that in mind, I ran the new model today for Central Virginia based on Gala’s green tip and full bloom dates (March 10 and April 4, respectively) that were kindly provided by our respected growers in the Central Virginia area. As shown in the image below, the model predicts that we have between 214-251 DD between April 28 and May 1st, which is our target window. The model also suggests carbohydrate surplus during that period which on one hand is good for supporting cell division and consequently good fruit size; but on the other hand, it will make thinning a bit harder. Therefore, the recommendation is to increase thinning rates by 30% during that period. For instance, if you would normally use 6-BA at 48 oz/100 gal, you should increase it to 62 oz/100 gal. This is still among the rate range of 48-64 oz/100 gal we were recommending. To convert from dilute to concentrate applications, please refer to my blog post at (https://blogs.ext.vt.edu/tree-fruit-horticulture/2020/04/02/how-to-calculate-the-tree-raw-volume-trv-and-chemical-rates-for-concentrate-spraying/). Also, for thinning materials to be used for other varieties, e.g. Fuji, Honeycrisp, Pink Lady, Golden Delicious, Red Delicious, and Ginger Gold, please refer to my other blog post at (https://blogs.ext.vt.edu/tree-fruit-horticulture/2020/04/02/fruit-thinning-scenarios-2020/).
One final point to highlight here is the effect of temperature on the activity of thinning materials. It has always been suggested that the best thinning activity by 6-BA and NAA is achieved when temperatures at and after the day of application are greater than 65 oF. By taking this into consideration and based on the 10-day weather forecasting for Batesville, this coming Saturday and Sunday, May 2 and 3, would be good days for thinning applications.
Should you have any questions/comments, please feel free to use the comments box below, call me at 5402326035, or shoot me an email at: firstname.lastname@example.org. Wish you all good luck with your thinning applications.
Defruiting newly planted and young apple trees (e.g., 2nd and
3rd leaf) allows trees to fill their allotted bearing space, grow to the top
wire and become ready to bear a decent crop by the fourth and fifth year.
Although defruiting can be performed manually by removing flower clusters or by
hand-thinning small fruitlets, many chemical options can make defruiting much
more comfortable and less labor-dependent. These include:
a) Using blossom thinners: Two products of lime sulfur are now
labeled for blossom thinning in Virginia. These are Rex lime sulfur and
NovaSource lime sulfur. Two to three applications of lime sulfur at 3% (3
gallons/100 gallon per acre) mixed with oil (e.g., JMS Stylet-oil) at 2% will
be enough to prevent the fertilization and fruit set of the majority of king
and side blossoms. However, blossoms thinning sprays should be avoided when
daytime temperatures are favorable for fire blight infections, e.g., between 75
to 85 oF, or when fire blight models (e.g., Maryblyt) predict
b) Using post-bloom thinners (recommended): chemical products
containing 6-BA (e.g., Maxcel and Exilis plus) or NAA (e.g., Fruitone L, PoMaxa
and Refine 3.5WSG) can be applied in combination with carbaryl (e.g., Sevin XL
plus) to remove apple fruitlets. One application at petal fall and another
application at fruit size 6-12 mm, will be sufficient. 6-BA at 100 ppm (64 fl
oz) or NAA at 15 ppm (6 fl oz) combined with carbaryl at 1 qt/100 gal/acre
should achieve satisfactory results. Please note that some forms of 6-BA and
NAA may contain a higher percentage of the active ingredient. So, it’s always
advisable to read the label and use the fl oz amounts that correspond to 100
ppm and 15 ppm of 6-BA and NAA, respectively. It should also be noted that NAA
is not recommended for Fuji and Delicious. Defruiting with 6-BA or NAA will be
more efficient if trees are under carbohydrate deficit conditions. The
carbohydrate thinning model on NEWA (http://newa.cornell.edu/index.php?page=apple-thin)
predicts the carbohydrate status of the tree based on daytime temperatures and
solar radiation values. The best defruting will be obtained when the 4-day
average balance is between -40 to -80 g/day. If the model is not accessible,
6-BA and NAA sprays should be applied when daytime temperatures are ≥ 85 o. Cloudy days at and after spray applications should also be
targeted. Adding a non-ionic surfactant (e.g., Regulaid) to the spray tank will
also enhance the efficacy of defruting applications.
The following figure shows the effect of two defruting
treatments on the fruit set (%) and crop load (fruit/branch cross-sectional
area) of Honeycrisp and GoldRush trees, respectively. Defruiting sprays were
applied twice at fruit size 6-18 mm.
c) Ethephon and carbaryl application (less recommended, especially for trees on dwarfing rootstocks): This combination will remove most fruit, but may cause tree growth reduction and increase flowering in the following year. The recommended rate for this application is 1 – 1.5 pt of ethephon tank mixed with 1 qt of carbaryl and 1 qt of Superior oil/100 gal/acre. Apply when fruit size is between 10 and 15 mm and daytime temperatures are between 75 – 90°F.
Sherif M. Sherif, Assistant Professor
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: email@example.com
Please find below an email I received from Mr. Dudley Dabbs (Fine Americas, Inc.) regarding mixing Kudos in the spray tank with Ca products.
“For years, Fine has cautioned against using Calcium containing formulations in the spray tank with Kudos PGR. The attached data (below) indicates that when using a (more expensive) highly complexed or Chelated Calcium product that has NO Free Calcium in it’s formulation may be mixed with Kudos PGR effectively. In addition, the attached data indicates that using a Calcium product with Free calcium in the formulation Mixed in the spray tank with Kudos will render Kudos ineffective as a PGR. IT WILL NOT WORK.
Please NOTE: This data is specific to KUDOS and does not include other Prohexadione Calcium formulations such as APOGEE. APOGEE and Kudos formulations are not the same. They are different from each other and you should NOT make the assumption that certain Complex Calcium Formulations that work OK with Kudos may NOT WORK OK with APOGEE”.
Here are the powerpoint slides showing results of Kudos and Ca tank mixes on pear
Sherif M. Sherif, Assistant ProfessorVirginia 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: firstname.lastname@example.org
Tree row volume TRV is the water volume needed to spray the tree canopy to the point of runoff. This is also defined as the dilute volume. Some might believe that 100 gals/acre is the dilute volume, but this is not true in all cases. TRV can considerably vary from one orchard block to another depending on planting density, tree height, and treewidth. Please see the equation below:
TRV = (Tree height X Tree width X
43,560 X 0.7) / (Between row spacing X 1000).
Example 1: You have a 7-year old Gala block planted at spacing 4’X12’ and the trees reached 1’ above the top wire (10’). How much water volume is needed to adequately cover all trees/acre to the point of runoff?
TRV = (11 X 8 X 43,560 X 0.7)/ (12
X 1000) = 223 gallons (~ 200 gal/acre).
Please note that younger trees and trees on very dwarfing rootstocks (e.g. B.9) might require less than 200 gals (probably between 100-150 gal), despite being planted at the same spacing (4’X12′). For instance, if you have a 5-year-old Honeycrisp/B.9 orchard planted at 4’X12′, and trees haven’t filled their allotted space yet. In this case, tree width would be around 6 feet (3′ in each side) and therefore TRV for this block would be 167 gals (You may round it to 160 gals) instead of 200 gals.
It is crucial to determine the TRV for each block in order to make further calculations for the chemical materials that you should apply at concentrate spraying. For instance, if your TRV is 200 gal/acre, and you set-up your sprayer at 100 gal/acre. In this case, you should add 2X the rate of each chemical (except surfactant and oil) in the spray tank, to get the same effect you would get if you applied the regular rate at the point of runoff (200 gal/acre).
Example 2: The recommended rate of thinning materials at petal fall for Gala is (48 oz of 6-BA) and (1 pint of sevin)/100 gal dilute. How much chemical materials you should add to a 500-gal spray tank if the TRV for your Gala block is 200 gals/acre?
In this case, you need to add 2X rate of each
chemical (at dilute/acre).
6-BA = 48 X 2 X 5 = 480 oz/500 gal +
Sevin = 1 X 2 X 5 = 10 pints/500 gal to cover
5 acres at concentrate.
Example 3: You decided to turn-off the bottom half of the nozzles and focus your thinning sprays on the top part of the tree (which I generally recommend for thinning sprays). In other words, each acre will receive only 50 gals of the spray mixture. How much 6-BA and Sevin you should add to your 500 gal spray tank if the TRV is 200 gals/acre?
In this case, you need to add 4X rate of each
chemical (at dilute/acre).
6-BA = 48 X 4 X 5 = 960 oz/500 gal +
Sevin = 1 X 4 X 5 = 20 pints/500 gal to cover
10 acres at concentrate.
Should you have any questions or comments, please don’t hesitate to call me at 540-232-6035, or email me at: email@example.com. You can also use the comments section below to send questions and comments.
Sherif M. Sherif, Assistant ProfessorVirginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center 595 Laurel Grove Road, Winchester, VA 22602
Thinning rates used at bloom (liquid lime sulfur 1.5% and 2% JMS stylet-oil) will not cause enough thinning if used as a stand-alone thinning treatment, but it will likely remove some blooms that will be tough to thin at later stages. One blossom thinning treatment at 20% open bloom is enough for this purpose.
6-BA applications at petal fall will serve a dual purpose: a) to improve fruit size, especially in Gala, and b) to open up fruit clusters.
Using NAA at petal fall will also sever a dual purpose in Honeycrisp: a) to improve return bloom, and b) to open up tight clusters.
Thinning at 6-12mm fruit size is the main fruit thinning window for most apple varieties. Thinning rates and timing at this stage should be determined based on the outputs of the apple carbohydrate thinning model available at NEWA website (http://newa.cornell.edu/index.php?page=apple-thin). I will run the model as usual and share with you the model outputs and recommendations through this blog.
Using 6-BA and NAA with carbaryl at 13-18 mm can also provide satisfactory results, but the efficacy of these chemicals will also be dependent on the tree carbohydrate level. So, it’s recommended to follow the model outputs at this stage as well.
Rescue thinning treatments (at 19-25 mm fruit size), might be necessary if earlier thinning attempts did not achieve satisfactory crop loads.
To improve return bloom in Honeycrisp it is highly recommended to apply four applications of NAA (2 oz/100 gal) at 10 days intervals, starting from 26-35 mm fruit size. Because NAA causes pygmy fruits in Fuji, NAA should be replaced by ethephon applications at 0.5 pt/acre to improve return bloom in Fuji.
Some varieties, e.g. Pink Lady and Ginger Gold, are easier to thin than others, and it can be easily thinned at the 6-18 mm fruit size window.
Important: all the rates suggested in these two charts are based on 100 gal/acre.
I hope you find this information useful. Should you have any questions or comments, please don’t hesitate to call me at 540-232-6035, or email me at: firstname.lastname@example.org. You can also use the comments section below to send questions and comments.
Sherif M. Sherif, Assistant ProfessorVirginia Tech, School of Plant and Environmental Sciences,AHS Jr. Agricultural Research and Extension Center 595 Laurel Grove Road, Winchester, VA 22602
Table 1: Chemicals and plant growth regulators labeled for fruit thinning in Virginia
Table 2: Thinning chemicals and rates recommended for petal fall-5 mm fruit diameter
Table 3: Thinning chemicals and rates recommended for 6 mm-15 mm fruit diameter
Table 4:Chemicals and rates recommended for rescue thinning applications (at 16-25 mm fruit diameter)
Sherif M. Sherif, Assistant ProfessorVirginia 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: email@example.com
The following is an updated version of a factsheet my former M.Sc student (Mr. Chester Allen) and I published last year on the VCE website (https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/spes/spes-110/SPES-110.pdf). I updated it to reflect what we have learned from our research in 2018 and 2019, particularly as it relates to the concentrations of lime sulfur and oil that could achieve good thinning activity and fruit quality.
What is Chemical Apple Blossom
thinning in apple orchards is the practice of spraying chemicals during the blossom
time to thin the crop.
thinners are sprayed multiple times during the bloom period in order to reduce
or prevent the fertilization of a portion of the blossoms that would cause
undesired crop loads if left to set fruits.
thinning can be used as a supplemental and/or alternative practice to standard
fruit thinning sprays.
What are the Benefits of Apple
size, optimized crop load, improved annual bearing, increased return bloom, and
more predictable thinning results are all benefits of chemical blossom thinning
blossom thinners can provide partial early season disease suppression and are
registered for organic use.
What Chemicals &
Rates can be used for Apple Blossom Thinning?
Currently, the only products registered for use as apple blossom thinners in Virginia are Rex Lime Sulfur Solution (28% Calcium Polysulfide) and NovaSource Lime-Sulfur Solution (29% Calcium Polysulfide). Label rates for these products range from 4% to 12% of formulated product per volume of spray solution when spray oil is NOT used. When spray oil is used, label rates of these products range from 1% to 3% of formulated product per volume of spray solution.
Mineral oils (dormant & summer) and fish oils may be combined with lime sulfur solutions and used as spray adjuvants to increase thinning effectiveness. Label rates for oil range from 0.5% to 2% depending on the type of oil used.
Based on our research in 2018 and 2019, application rates of 3% lime sulfur and 2% JMS stylet oil causes severe russeting and reduces fruit packout significantly, whereas low rates (e.g. 1% lime sulfur and 1% JMS stylet oil) have no significant thinning effect. Blossom thinning using 1.5-2% lime sulfur and 2% oil showed good thinning results and less fruit russeting.
If blossom thinning is to be followed by chemical fruit thinning (e.g. by 6-BA and NAA), we would suggest using 1.5% lime sulfur and 2% oil for blossom thinning. Our research also indicated that both forms of lime sulfur (Rex Lime Sulfur Solution and NovaSource Lime-Sulfur Solution) were equally effective.
Blossom thinning using high rates of lime sulfur (3%) and oil (2%) can also be used for defruiting young apple trees.
When & How
Frequently Should Blossom Thinners be Applied?
Determining when to apply the first blossom thinning spray and how frequently to reapply blossom thinning sprays are the most important decisions to make when using blossom thinning sprays to thin and manage the crop load.
The first blossom thinning spray should be applied once a sufficient number of blossoms have been fertilized to set the desired crop load.
After the first blossom thinning spray, additional blossom thinning sprays will need to be re-applied approximately every 2-4 days, depending on temperature, to prevent the remaining blossoms from becoming fertilized and setting fruit. No more than three applications of lime sulfur solution can be applied for blossom thinning per year.
Our research on Gala apples has indicated that applying blossom thinners at 20% open bloom, followed by another application 48h or 72h later, results in smaller crop loads and better fruit size compared to untreated (unthinned) trees.
What is the Pollen
Tube Growth Model (PTGM)?
The Pollen Tube
Growth Model (PTGM) model, developed by researchers at Virginia Tech, is a
useful tool for assisting in deciding when to first apply and re-apply blossom
The model collects
weather data and uses style length (mm) to predict the time a pollen tube would
take to reach an ovule and achieve fertilization.
Based on inputs
provided by weather stations and users (e.g. cultivar, style length and the
model start time), the model provides the day/time for the first thinning
application and subsequent thinning sprays if required.
cultivar-specific model has been generated and tested for seven apple
varieties, including Red Delicious, Golden Delicious, Cripps Pink, Honeycrisp,
Fuji, Gala and Granny Smith.
Our research on
Gala apples indicated that applying thinning treatments at 20% bloom + 48h or
72h later, produces similar results to thinning applications guided by the
Sherif M. Sherif, PhD, Assistant ProfessorVirginia Tech, School of Plant and Environmental Sciences,AHS Jr. Agricultural Research and Extension Center 595 Laurel Grove Road, Winchester, VA 22602 Te. 540-232-6035, Email. firstname.lastname@example.org
Q: Can I do notching for trees right after planting to
increase the number of feathers?
Yes, if you get trees from nursery with a little number of branches (feathers), you can use notching to induce branching. This is mainly important for trees intended for high-density training systems (e.g. tall spindle) and to avoid or reduce the chances of blind wood. Younger trees are more responsive to notching than older trees. You can use a hacksaw or a small knife to cause a notch above the bud as shown in the image attached. In notching, we remove a very small piece of bark without hurting/damaging the wood. This promotes branching by disturbing the hormone (auxin) that prevents the formation of lateral shoots. You should mainly target the area between 30-60 inches above the soil surface for notching. Although you can start notching directly after planting, waiting until new shoots are between 1-3 inches long would be better as you can easily distinguish the buds that failed to break.
Q. Does applying PGRs to the notched area increase branching
in the newly planted trees?
That’s right. You may consider adding a 6-BA compound (e.g.
Promalin) to the notched area by using a high concentration (12 oz in 5 gallons
of water) and a backpack sprayer. Other researchers even suggested mixing
Promalin and Maxcel and spraying them together to induce branching and enhance
the growth of the new shoots. To do so, you need to mix 5 tablespoons of
Maxcel, 1.5 tablespoons of Promalin and 2.4 ml of Regulaid (a surfactant) in a
1-quart spray bottle and spray it as a mist to the notched area. This will
enhance branching significantly.
Q. Is notching and PGR applications effective with older apple
For 1 and 2-year old apple trees, notching alone can be effective
but again, a mist spray of Promalin alone or Promalin and Maxcel as indicated
above will enhance branching and help the tree fill the space much quicker.
This time of the year (between the tight cluster and open cluster) is just
perfect for both notching and PGR applications. You may still do that until full
bloom and after bloom, but the risk of shoot blight increases after bloom and
notched areas will serve as entry sites for the fire blight bacterium. This
risk can also be partially with seasonal streptomycin sprays. The same rules
apply for enhancing branching on the blind wood of older apple trees (> 3
Q. Can I just use PGRs applications without notching to induce
branching in non-bearing and bearing apple trees?
Yes, you can use 6-BA products alone but you have to follow the
instructions on the label for the concentration and application timing for
bearing and non-bearing apple trees. You can use Maxcel at 250-500 ppm (128
oz/40 gal/acre) to induce branching in non-bearing apple trees. Applications
should be made when terminal shoots are 28-30 inches long. For bearing apple
trees, you can use spray Promalin solution to the blind wood at a concentration
of 0.25-1 pint in a 5 gal of water, applied at 1-3 inches of new terminal
Q- I have a lot of blind wood in the top part of the tree; is
there anything other than notching and PGRs I can do to fix that?
At the time of dormant pruning, I would suggest you remove 2-3 large limbs by making a bevel cut and follow this with notching and PGR sprays two weeks before bud break. Leaving many large limbs in the tree sucks up the carbohydrate resources from the main trunk and makes it hard for any new branches to develop in the leader, causing blind wood.
Dr. Sherif M. Sherif, Assistant Professor, Virginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center, 595 Laurel Grove Road, Winchester, VA 22602. Email: email@example.com; Tel: 540-232-6035