Tag Archives: Thinning

MaluSim Carbohydrate Model for May 6, 2014

Today, I ran the MaluSim model for both Central Virginia <pdf> and  Winchester <pdf>.

Central VA MaluSim 5_6_14 Winchester MaluSim 5_6_14

For Central Virginia, fruitlets are just starting to approach the 10 mm stage. It looks like the best chance to get a strong thinning response will be Wednesday and Thursday. After that, the model is showing that chemical thinners will have more of an “average” response. Target blocks that have a heavy crop load on Wednesday and Thursday, and leave blocks with more frost damage and lighter crop loads to thin on Friday and over the weekend.






Table 1. Fruitlet sizes at Silver Creek Orchards.

1-Apr 28-Apr 30-Apr 2-May 6-May
Empire Silvertip Petal Fall 5.6 7.3 10.9
Red Delicious 5.7 6.5 9.3
Pink Lady 5.4 7.5 8.3
Gala 5.4 6.4 8.8
Fuji 4.4 5.8 7.8

For the Winchester area, most blocks are at petal fall or just beyond. We’re forecasted to have some summer-like weather over the next several days, which will cause a fairly strong carbohydrate deficit in the trees. Petal fall thinning sprays rarely over thin, even in hot weather, however blocks with fruitlets approaching 10 mm may see a strong thinning response from applications made over the next three to four days.

I will run another set of models on Friday. I will also start posting fruitlet sizes from fruit at the AREC. Download the above linked pdf files to view the full reports.

MaluSim Carbohydrate Model for May 2, 2014

Fruitlets in Central Virginia are growing fast, and I suspect that most growers will be putting on their 10 mm thinning sprays over the next 7 days. In the Winchester area, we’re just at petal fall, so I will start running the MaluSim model next week.

For Central Virginia, using Intellicast forecasts, the MaluSim model is predicting a slight carbohydrate deficit through the early part of next week. Growers should expect a normal to slightly aggressive response from their chemical thinners that are applied today through Monday. I’ll run another model on Tuesday to assess the impact of thinner applied in the middle to end of next week.

Table 1. Fruit phenology at Silver Creek Orchard.

1-Apr 28-Apr 30-Apr 2-May
Empire Silvertip Petal Fall 5.6 mm 7.3 mm
Red Delicious 5.7 mm 6.5 mm
Pink Lady 5.4 mm 7.5 mm
Gala 5.4 mm 6.4 mm
Fuji 4.4 mm 5.8 mm

Download the full report <Peck Central VA MaluSim 5_2_14>.

MaluSim Carbohydrate Model for April 30, 2014

Growers in the Central Virginia growing region are reporting that their bloom is stretched out quite a bit with some side bloom still in flower and some king bloom fruit approaching 5 to 6 mm in fruitlet size. In general, most chemical thinners are more active on the smaller, slower growing fruit, so this spread may prove to be advantageous.

Peck Central VA MaluSim 4_30_14

For those Central Virginia growers who are starting to map out their thinning schedule, I’ve started running the MaluSim carbohydrate model. I will discuss the details of how the model works, as well as my research results on validating the model at the meeting on Thursday, May 1.

The MaluSim model is most effective at predicting thinning efficacy at the 10 mm timing, and has a much lower predictive value for flower, petal fall, or 20-25 mm thinning applications.

As of today, the long-term forecast shows a long string of days with mild temperatures and lots of sun. From these forecasted data, the MaluSim model <<pdf>> is showing no extremes in carbohydrate supply, meaning that chemical thinners will have a “average” response. For a detailed look at the model, as well as interpretation table, download the above linked pdf.

For the Winchester area, I will assess fruit development on Friday to decide when the first model run is warranted.

A big thank you to John Saunders for helping with the MaluSim modeling work this year. Last year, Dr. Mizuho Nita (grape plant pathologist at our AREC) installed weather stations at Silver Creek and set up a network relay system that allows me to download meteorological data from Silver Creek right to my computer. If you work with Mizuho on grape disease related issues, please thank him as well!

Notice of Date Change for Central Virginia Orchard Meeting

April 29, 2014

Dear Central Virginia Fruit Producer:

Due to the quick progress of our trees this spring, our third orchard production meeting of this year HAS BEEN MOVED FORWARD TO THIS THURSDAY, May 1st. We will be meeting at 11:00 a.m. at the office of Saunders Bros. Nursery, located at 2717 Tye Brook Hwy, Piney River, VA 22964; Tel.: (434) 277-5455; http://www.saundersbrothers.com/. Bennett Saunders will be our host.

A special focus of this meeting with be crop thinning considerations provided by Extension specialist Gregory Peck. In addition, Drs. Yoder and Bergh will be on hand to discuss disease and insect pest issues, respectively. Please come to discuss fruit production issues and concerns with other fruit growers and Extension fruit specialists. You are encouraged to bring plant and insect samples for identification, but please have these contained in a plastic bag.

Please bring your own bagged lunch to this meeting. Cold drinks will be provided by the host orchard.

Orchard Events Website:


Remaining 2014 Central Virginia Orchard Meeting Schedule

· May 20th Fitzgerald Orchard Lowesville, VA

· June 3rd 7K Farm Rustburg, VA


Michael W. Lachance

Extension Agent

If you are a person with a disability and desire any assistive devices, services or other accommodations to participate in this activity, please contact the Nelson County Extension Office at (434) 263-4035 to discuss accommodations five days prior to the date of the meeting.

MaluSim Carbohydrate Models: 2013 Season Recap for Winchester and Central Virginia

Slide3 Slide3Attached are the final MaluSim carbohydrate models that I will run for 2013.

Please print out a copy of the below pdf file to add to your records. Later in the season, I will be asking for feedback from you about how you used the model, how well the model predicted thinner response in your orchard, and if I should continue running the model in future years. Please feel free to send me additional feedback at anytime.

Peck Central VA MaluSim 5_29_13

Peck Winchester VA MaluSim 5_28_13

Suggestions for late thinning and return bloom applications

By this time, apples in most of Virginia are 13-20 mm in fruit size. Once apples reach this size, the trees tend to be less responsive to the typical 10 mm (carbaryl plus NAA or 6-BA) applications. However, if additional thinning is needed, growers can still use ethephon (sold under the trade names Ethrel and Ethephon 2). Ethephon is most effective when fruit size is 14 to 28 mm in diameter. In most years, it is difficult to chemically thin apples larger than 24 mm.

Ethephon has variable responses due to air temperature and humidity, as well as spray water volumes. Overthinning is more likely with this material than with other thinners. For this reason, ethephon has been primarily used when earlier thinning applications were not successful, on very difficult to thin cultivars, and/or when return bloom has been a severe problem. Thinning results with ethephon varies amongst cultivars. Ethephon is not very effective on Gala, but it is very effective on Golden Delicious and Rome. Where water is alkaline, buffering the spray solution to a pH of 3 to 5 will increase chemical stability and effectiveness. Do not use before a light rain or dew or when post-application temperatures are predicted to be greater than 90˚F because excessive thinning may occur.

Ethephon is usually combined with carbaryl or oxamyl (Vydate L). For greater thinning activity, ethephon can also be tank mixed with NAA and/or spray oil.

I have several research trials underway to look at alternative and hopefully more consistent late thinning materials. However, at this time, ethephon is still the standard material when fruit size is greater than 14 mm.

Once fruit is larger than 28 mm, hand thinning will need to be used to remove additional fruit. Hand thinning will have a positive impact on final fruit size and return bloom for up to about 45 days after full bloom. In 2013, this is around the first week of June for central Virginia and the second week of June for the Winchester area.


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 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 Models for May 20: Winchester and Central Virginia

On May 20, I ran the MaluSim carbohydrate model for Winchester and Central Virginia. This will be the last MaluSim posting using forecasted data for the season. Sometime in the week or two I will post a season recap using only recorded data.

Slide3Slide3In Winchester, as predicted, we have been experiencing hot and cloudy weather over the last few days. Thinning applications made from late last week through Monday will likely be fairly active, with some easy to thin cultivars (e.g. Red Delicious) potentially having significant fruit drop. However, from Tuesday through the end of the coming week, growers should expect an average response from their thinning applications.

In Central Virginia, there was a similar trend but with somewhat cooler daytime temperatures, the carbohydrate deficits were less severe. Similar to Winchester, thinning applications made over the next several days should have a fairly typical response.

Peck Winchester VA MaluSim 5_20_13

Peck Central VA MaluSim 5_20_13

Fruitlet sizes and growth rates at the Winchester AREC:

  • Empire: 19.1 mm; 1.5 mm/day
  • Fuji: 13.6 mm; 1 mm/day
  • Gala: 13.8 mm; 0.8 mm/day
  • Pink Lady: 14.1 mm; 0.9 mm/day
  • Red Delicious: 13.8; 0.9 mm/day


MaluSim Carbohydrate Models for May 16: Winchester and Central Virginia

MaluSim models were run on May 16 for Winchester and Central Virginia.


As I spoke about at the Winchester breakfast meeting on Thursday morning, the Winchester forecast is calling for warm and cloudy weather starting today and running through most of next week. From many year’s of research, we know that these are the conditions under which there is a fair amount of natural thinning and that chemical thinners can be particularly active. When the weather data is run through the MaluSim model, we see that there is a carbohydrate deficit between -40 to -60 g CHO/day predicted for the next 10 days. This means that chemical thinners that are applied over the next several days will likely be fairly active. With this in mind, growers should consider reducing rates and/or not using a surfactant. Growers with blocks that sustained freeze damage on Tuesday morning, should consider further reducing rates. As always, you should be checking your trees and making decisions based upon the conditions in your own orchard.

For Central Virginia (Piney River), the carbohydrate deficits over the next week will remain in the negative, but not be as low as the Winchester area. This means that chemical thinners applied from today through the weekend will likely be slightly aggressive when used at standard rates. Growers should be regularly checking their blocks for current conditions. By now, you should be able to see some effect of the cloudy weather that the region experienced early last week.

Here are the pdf files that contain the weather data and the MaluSim models:

Peck Central VA MaluSim 5_16_13

Peck Winchester VA MaluSim 5_16_13


MaluSim Carbohydrate Models for May 13: Winchester and Central Virginia

Slide3Slide3The MaluSim carbohydrate model was run on May 13 for both Winchester and Central Virginia.

In Central Virginia, many later blooming cultivars are around 10 mm fruitlet size and can still be chemically thinned. From applications made over the past weekend, growers can expect average responses to chemical thinners. As we move through the week, greater and greater carbohydrate deficits are predicted, which will increase the potency of chemical thinners.

For Winchester, the model is predicting mild carbohydrate deficits early in the week, and much more severe deficits towards the end of the week and over the weekend. Applications made this past weekend through the middle of the week will likely have an average to slightly aggressive response. However, applications make towards the end of the week may result in very aggressive thinning activity. If the weather forecasts hold up, growers should consider reducing rates for applications made towards the end of the week.

I will run the model again on Thursday, May 16.

Fruitlet sizes from the Winchester AREC:

  • Honeycrisp: 8.8 mm
  • York: 8.0 mm
  • Fuji: 8.6 mm
  • Suncrisp: 8.4 mm
  • Pink Lady: 9.2 mm
  • Empire: 11.8 mm

One more note, there are widespread frost/freeze predictions for most of Virginia for Tuesday morning. If a significant frost/freeze event occurs, growers should be cautious with their thinning applications until they can assess if damage has occurred. However, the forecast for Winchester predicts the temperature will only go to 32F, which will not be cold enough to cause significant damage. The forecast for fruit growing regions to the south of Winchester appears to be in the mid-30s to low 40s.

To see more information, click on the linked pdf files below:

Peck Winchester VA MaluSim 5_13_13

Peck Central VA MaluSim 5_13_13

MaluSim Carbohydrate Models for May 9: Winchester and Central Virginia


MaluSim carbohydrate models for Winchester and Central Virginia were run on Thursday morning.


Over the next day or so, for Central Virginia, the carbohydrate balance will remain in the negative, but quickly move to the positive over the weekend. From thinning applications made Thursday (5/9) or Friday (5/10), growers should expect a fairly “normal” response. However, forecast data from Intellicast.com, suggests that sunnier, but cooler weather will move into Virginia early next week, followed by a warming trend starting on Wednesday. Based on the MaluSim model, this weather pattern will cause apple trees to have positive carbohydrate values through the early part of next week, and thus standard rates of thinners used on Saturday or Sunday will be less effective than expected. In blocks where heavier thinning is needed, growers should consider holding off on their 10 mm thinning application until Tuesday or Wednesday when warmer temperatures return. However, once fruit gets to be 15 mm or larger, NAA and 6-BA are less effective thinning agents. The other approach is to increase the rates used in thinning applications made over the weekend through Monday.

The above scenario is similar for Winchester but since fruit size is smaller (generally 6-8 mm), growers can wait for next week’s warming trend to make the 10 mm thinning applications. Additionally, with the smaller fruit size in Winchester, the cloudy weather that we’ve experienced over the last few days should cause less natural thinning than what might occur in Central Virginia.

I’ll run the model again on Monday.

Current fruitlet sizes at the Winchester AREC:

  • Empire: 8.0 mm
  • Golden Supreme: 6.3 mm
  • Fuji: 6.5 mm
  • Golden Delicious: 5.7 mm
  • Suncrisp: 6.0 mm
  • Pink Lady: 7.2 mm
  • Idared: 7.1 mm
  • York: 6.0 mm

For more information, download pdfs of the models:

Peck Central VA MaluSim 5_9_13

Peck Winchester VA MaluSim 5_9_13