Category Archives: Thinning

Accede: a new chemical thinning material for apples and peaches

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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

Chemical Options for Defruting Young Apple Trees

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Defruiting newly planted and young apple trees (e.g., 2nd and 3rd leaf) is recommended to allow 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. This practice is particularly advisable for trees on dwarfing rootstocks (e.g., B.9, G.41, and G.16). Although defruiting can be achieved manually by removing flower clusters and small fruitlets, several chemical options can make defruiting much easier and less labor-intensive. These include:

a) Using chemical blossom thinners: 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% should be enough to prevent the fertilization and fruit set of the majority of king and side blossoms. It is worth noting that blossom thinning applications should be avoided when daytime temperatures are favorable for fire blight infections, e.g., 75° to 85°F, or when fire blight models predict blossom infections. You may also consider applying streptomycin with or after bloom thinning applications to reduce the probability of infection. The two lime sulfur products labeled for blossom thinning in Virginia are Rex lime sulfur and NovaSource lime sulfur. Our research indicated that both products are equally effective.  

b) Using post-bloom thinners (recommended): 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 will be sufficient at petal fall and another at fruit size 6-12 mm. 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. 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 defruiting with 6-BA or NAA is more efficient when 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 results are obtained when the 4-day average balance is between -40 to -80 g/day. If the model is not accessible, 6-BA and NAA applications should be made when daytime temperatures are ≥ 85 oF. 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 fruit set (%) and crop load (fruit/branch cross-sectional area) of Honeycrisp and GoldRush. 

Trees of ‘Honeycrisp’ and ‘GoldRush’ were treated with a mixture of Maxcel+Carbaryl+Regulaid or PoMaxa+Carbaryl+Regulaid at petal all and at fruit size (10 mm). The time of application was determined by the Carbohydrate thinning model on NEWA.

c) Using a mixture of ethephon, carbaryl, and oil: 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. The best results are achieved when applying this mix at 10-15 mm fruit size and daytime temperatures 75 – 90°F. It should be noted that ethephon can severely inhibit tree growth, and therefore it is not recommended to use it for defruiting weak- and medium-vigor cultivars (e.g., Granny Smith & Honeycrisp) on dwarfing rootstocks (e.g., B.9).  

MaluSim models for 11 May 2015

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For both Winchester and Central Virginia, the Malusim model is predicting a mild to no carbohydrate stress over the next week. Although temperatures at the time of application, are less important then the carbohydrate running average (2+4 Running Average), expect chemical thinners applied Sunday (10 May) or Monday (11 May) to cause more thinning than applications made late last week or for the rest of this week. Expect a “typical” response from chemical thinners applied Tuesday (12 May) through the rest of this coming week.

Peck Winchester MaluSim 5_11_15Peck Central VA MaluSim 5_11_15

The National Weather Service is predicting sunny weather later this week, as well as daytime temperatures in the 70s. This should result in ideal conditions for plant growth, and thus less carbohydrate stress in the apple trees.

One of the weaknesses of weather-based models, is the need to use forecast data to make decisions about future events. When I ran the MaluSim models for both Winchester and Central Virginia last Thursday, the forecast was for hot, cloudy weather. Although it was in the mid-80s in most of Virginia over the weekend, there was also a lot more sunlight than predicted. Temperatures are generally a lot more reliable than cloud cover predictions, but both seemed to be less severe than originally forecasted.

Cloudy weather predicted for later in the week is causing wild swings in the MaluSim model output. My expectation is that actual carbohydrate levels will be more moderate and that running average values will remain in the 20 to -20 g CHO/day range.

Full model output:

Peck Winchester MaluSim 5_11_15.pptx

Peck Central VA MaluSim 5_11_15.pptx

MaluSim Model Data for 7 May 2015

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Due to warm days (>80F) and intermittent cloud cover, the MaluSim carbohydrate model is showing a strong carbohydrate deficit for both Winchester and Central Virginia over the next four to five days. Expect an aggressive to very aggressive response to chemical thinners applied today through early next week. Reduce rates, and/or do not include oil or other surfactants if overthinning is a concern.Peck Winchester MaluSim 5_7_15

Peck Central VA MaluSim 5_7_15

Pay close attention to the weather forecasts. If actual temperatures are closer to 90F and/or there are prolonged periods of cloud cover, then overthinning will likely occur.

The greatest amount of thinning occurs when fruitlets are on average between 8-12 mm in diameter. Thinning when fruitlets are slightly smaller or larger will result in less thinning, which may be desirable if there is a severe carbohydrate deficit.

Cooler temperatures forecasted for the middle to end of next week should result in less carbohydrate stress and reduced chances of overthinning. However, fruitlets that are greater than 15 mm in diameter are more difficult to thin with NAA or 6-BA.

During these warm days, expect the average fruitlet size to increase by at least 0.5 mm per day.

Full MaluSim model output:

Peck Winchester MaluSim 5_7_15.pptx

Peck Central VA MaluSim 5_7_15.pptx

Central Virginia MaluSim for 4 May 2015

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Warmer temperatures and cloud cover from some rainstorms later in the week will cause a moderately stronger carbohydrate deficit for Central Virginia.

Peck Central VA MaluSim 5_4_15

Thinning applications made Tuesday through Thursday will result in the strongest response this week. Long term weather forecasts predict days in the 80’s and nights in the 60’s for the next 10 days. Carbohydrate levels will likely remain in the 0 to -40 range during that period.  To get the strongest response possible, make your applications when average fruit size is 8-12 mm in diameter.

Due to a technical glitch, I was unable to run the MaluSim model for Winchester. I hope to have the problem resolved Tuesday morning. I will post an update for Winchester as soon as possible.

Full MaluSim report:

Peck Central VA MaluSim 5_4_15.pptx

Central Virginia MaluSim for May 1

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Moderate temperatures and adequate sunlight are resulting in slight carbohydrate deficits according to the MaluSim model.

Peck Central VA MaluSim 5_1_15

 

This means that chemical thinners applied today through the first part of next week should cause an “average” response. Warmer temperatures are forecast for the middle of next week, which should result in greater carbohydrate deficits. I will run another simulation for Central Virginia, as well as the first Winchester run on Monday.

Central Virginia MaluSim for 1 May 2015:

Peck Central VA MaluSim 5_1_15.pptx

MaluSim Model for Central Virginia, 27 April 2015

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Today, I ran the first Central Virginia MaluSim model for 2015. I will start the Winchester models later this week.

For Central Virginia, I use data from a weather station set up at Silver Creek Orchards and managed by my colleague, Dr. Mizuho Nita. A big thank you to Dr. Nita for allowing me to install the necessary instrumentation and for maintaining the station and associated software.

This year, I will be using forecast data from the National Weather Service. In past years, I used Intellicast.com data because they provided 10-day forecasts with cloud cover predictions. Intellicast no longer provides the cloud cover data in an easy to use format, so I am switching to the National Weather Service’s forecasts. Note that these forecasts only project five days into the future.

We will discuss the details of the model at Tuesday’s meeting at Saunders Brother. Peck Central VA MaluSim 4_27_15

However, this first model run suggests that the relatively cool weather, and mostly sunny weather that has occurred since bud break has resulted in a moderate carbohydrate deficit in apple trees. Growers can expect average results from chemical thinners applied the last couple-few days through to the weekend. In blocks where significant thinning is needed, growers should apply carbaryl at petal fall and then look to the warmer weather that is predicted for the weekend and early next week for their 10 mm application.

Central Virginia weather data, MaluSim data, and an interpretation chart are in the pdf linked to below:

Peck Central VA MaluSim 4_27_15

MaluSim Carbohydrate Model for May 27, 2014

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I ran a MaluSim model using data from the weather station located at the Alson H. Smith, Jr. AREC in Winchester. This will be the last model run for the year.

Slide3 No forecast data was used in this run. Based on the output, I would expect chemical thinners that were applied May 14-16 to have an average response, while thinners that were applied on and after May 17 to have minimal effect. The effectiveness of thinners is greatly influenced by fruit size, so if the model showed a carbohydrate status that was greater than 20 g per day, and fruitlets were greater than 15 mm at the time of application then chemical thinners may not have been particularly effective.

Growers should compare the results of their chemical thinning program with the modeled carbohydrate status to determine if the model accurately predicted the level of thinning you expected from your applications.

I would appreciate hearing from growers about how they used the model to make chemical thinning decisions. Both positive and negative feedback is appreciated.  You can use the comment feature in the blog site, or just send me an email.

Download the full report:

Winchester VA MaluSim 5_27_14

Late thinning of apple, return bloom, and peach hand thinning

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LATE (“RESCUE”) THINNING

Where late (14-25 mm) thinning is still possible growers can use the following materials and combinations of materials in order of greater thinning potency:

  1. ethephon (0.5 -1.5 pints/100 gal)
  2. ethephon + carbaryl (1 pint)
  3. ethephon + carbaryl + oil (1 quart)
  4. ethephon + carbaryl + oil + NAA (5 ppm)

Ethephon applications can cause over thinning, so use the lowest rates and tank mix with the least number of other materials unless significant fruit removal is desired.

PROMOTING RETURN BLOOM IN APPLE

Ethephon (sold under the trade names Ethrel and Ethephon 2) can promote flower bud formation when applied from petal fall to about 6 to 8 weeks after full bloom. The greatest effect is from applications made 0 to 4 weeks after bloom. However, since ethephon can cause substantial fruit thinning, multiple weekly applications at rates 1/2 that of the thinning rate are recommended starting when fruitlets are greater than 30 mm. When possible, it is best to wait until after “June” drop has occurred. At a minimum, wait 7-10 days after the last thinning application before starting ethephon return bloom sprays. Additionally, do not apply ethephon to trees that are stressed or trees that are low in vigor.

A single ethephon application can be used at a high rate (up to 900 ppm). However, more consistent results are often obtained from multiple (3-4) applications made at 10-14 day intervals using lower rates (150-300 ppm). One common, and often effective strategy, is to make two applications in June and two applications in July.

Another strategy is to make 2-4 applications of ethephon at 150 ppm tank mixed with NAA at 5-10 ppm (or 2.5-5 ppm when tank mixed with spray oil). This approach has been beneficial for strongly biennial cultivars.

Sensitivity to ethephon is very different amongst cultivars, thus it is important to choose a rate specific to each variety. Do not exceed 8 pints per acre per year. If trees are over-cropped ethephon may not effectively give adequate return bloom the following season. Higher soluble solids and lower starch levels at harvest may be expected with some cultivars, particularly with high rates and/or late season applications. No loss of firmness has been detected with ‘Red Delicious’ at the optimum harvest date.

Ethephon sprays can reduce tree growth (dependent on timing and amounts used) and thus may not be desirable for young non-bearing trees if maximum tree growth is desirable.

HAND THINNING PEACHES

Hand thinning peaches to 6-8 inches apart on the branch will result in increased final fruit size and help prevent limb breakage. This activity will be most effective when completed over the next couple-few weeks. Hand thinning peaches later in the season will not have as much of an impact on final fruit size.

MaluSim Carbohydrate Model for May 22, 2014

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On Thursday, I ran the MaluSim model for Winchester.

Slide3

As I suggested in my last post, the strongly negative carbohydrate balance forecasted for May 20 and 21 were a product of poor cloud cover forecasting. In fact, since May 16 the carbohydrate status has been in the positive range. Chemical thinning applications made from May 17 through the next several days will likely have an moderate to poor response. Now that fruitlets are 15 to 20 mm in diameter, NAA and 6-BA will have minimal thinning efficacy. Growers who need to thin additional fruit from their trees should consider ethephon applications.

Table 1. Fruitlet sizes at the Alson H. Smith, Jr. AREC in Winchester, VA.

Variety 12-May 15-May 20-May 22-May
Empire 10.4 12.2 15.1 17.9
Fuji 7.0 9.0 12.1 14.8
Gala 8.7 11.3 13.9
Goldens 8.0 9.5 12.7 14.9
Idared 8.1 9.5
Pink Lady 9.2 11.0 13.6 16.6
Red Delicious 8.0 10.1 11.4
York 7.9 10.7 13.8 16.1

As I did for the Central Virginia models, I will run one more season recap model early next week.

Download the full report:

Winchester VA MaluSim 5_22_14