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: ssherif@vt.edu. Wish you all good luck with your thinning applications.

Greetings,

                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: ssherif@vt.edu

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: ssherif@vt.edu.  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

Please note the following:

• 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: ssherif@vt.edu.  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

Greetings,

I just wanted to share with you some of the slides and information I presented this past Tuesday via zoom in case you haven’t had a chance to attend the meeting. You may also consider reading my previous blog post on blossom thinning (https://blogs.ext.vt.edu/tree-fruit-horticulture/2020/03/28/apple-blossom-thinning-general-overview-and-updates/) and the factsheet on the Virginia Cooperative Extension webpage (https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/spes/spes-134/SPES-134.pdf) if you want to get a better idea about the science and application of chemical thinners, e.g. 6-BA, NAA and ethephon.

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: ssherif@vt.edu

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 trees?

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 years).

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 growth.

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: ssherif@vt.edu; Tel: 540-232-6035 

Greetings,

               I just wanted to update you on where we are right now in terms of flower bud development in apple and stone fruits and whether we will potentially be affected by the cold weather this weekend (Sunday). As for apples, almost all our apple cultivars in the ASH Jr. AREC’s research farm are in the silver tip, green-tip or ½ inch green now (see the table below). Pink Lady and Zestar are the only cultivars we have that show buds in tight-cluster and first-pink stages. None of the buds I investigated in Pink Lady and other commercial cultivars showed signs of frost damage so far. Based on the weather forecast for the Winchester/Frederick county area, temp-Max will range between 41-78 ^oF and temp-Min will range between 31-42 ^oF in the next 10 days. If this turns out accurate, then we should not really be worried about frost damage to our apple blossoms for the next 10 days.

What about stone fruits? Well, based on the few apricot and plum trees we have in the lab, our plum and apricot trees are in the full-bloom and post-bloom stages now and although we had temp. of 31 ^oF this past Monday (Mar 16) for a couple of hours, the damage to apricot and plum blossoms that could be due to frost is less than 5%. It’s also unlikely that temps this Sunday would cause any significant damage to apricot and plum flowers unless they will drop below 25 ^oF. Our sweet cherries, on the other hand, are still between the green-tip and tight-cluster stages and therefore, the risk of frost damage is also minimal. Most of our peach cultivars are moving slowly toward 1-2% bloom and with temps of 78 ^oF tomorrow (Friday), this percentage might jump to 5-10%. At this stage, the temperature that can kill 90% of buds is 24 ^oF, which is not the case this Sunday, at least for most parts of the state. For more information about critical temperatures for bud developmental stages, please use this link/PDF (https://www.canr.msu.edu/uploads/396/36740/PictureTableofFruitFreezeDamageThresholds.pdf. You may also need to print a color version of this figure and keep it in your house/office as a reference.

If you are not done with apple pruning yet, for very obvious reasons, and wondering whether you should proceed with the blocks that are not pruned, I would not generally recommend doing any pruning at this stage, for two reasons: 1) trees have already lost their cold hardiness and they would be more sensitive to any low temperatures during and after pruning; 2) there is a high risk of fire blight/shoot blight if the pruned wood did not heal well enough before the full-bloom window. As for peaches and nectarines, I usually recommend pruning the trees 4-6 weeks after full bloom.

If you have any questions or comments, please send them in the “comments” window below, send me an email at: ssherif@vt.edu, or call me at my office number: 540-232-6035 and I will make sure to get back to you as soon as I can.

Stay Safe, everyone.