Tag Archives: apple

MaluSim models for 11 May 2015

Posted on May 11, 2015 by Greg Peck

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.

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

Posted on May 7, 2015 by Greg Peck

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

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

Posted on May 4, 2015 by Greg Peck

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

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

MaluSim Model for Central Virginia, 27 April 2015

Posted on April 27, 2015 by Greg Peck

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.

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

Impromptu Pruning Discussion, Monday February 23

Posted on February 20, 2015 by Greg Peck

I will be meeting with Bennett Saunders and a few other growers at Saunders Brothers’ Cub Creek Orchard this coming Monday to discuss pruning strategies for tall spindle and other high density orchards.

This will be a fairly informal meeting oriented towards group discussion and demonstrations.

For those who can make it, we will meet at 10AM just inside the gate near the entrance of Cub Creek Orchard located off of Carter Hill Lane, Roseland, VA.

Click here for Google Map directions.

It looks like it’ll be decent weather, but the ground might be a bit wet. Bring your own lunch, loopers, boots, etc.

UPDATE (Sunday Feb. 22): This meeting is still scheduled to proceed as planned. However, only four wheel-drive vehicles will be able to drive further than the orchard entrance. We will coordinate carpools at 10AM.

________________________
Gregory Michael Peck, Ph.D.
Assistant Professor of Horticulture • Virginia Tech
Alson H. Smith, Jr. Agricultural Research and Extension Center
595 Laurel Grove Road • Winchester, VA 22602 • USA
540.869.2560 X19 greg.peck@vt.edu
Tree Fruit Homepage: www.anr.ext.vt.edu/tree-fruit/
Research Homepage: www.arec.vaes.vt.edu/alson-h-smith/treefruit/horticulture/

Predicted 2014 Apple Harvest Dates

Posted on July 24, 2014 by Greg Peck

Predicting harvest date depends upon many factors, including full bloom date, accumulated heat units (growing degree days) over the course of the growing season, physiological stressors (e.g., disease and insect damage or drought), day to night temperature differentials as harvest approaches, and the amount of precipitation. However, the number of days between full bloom and harvest has been shown to be the most reliable predictor of harvest date.

Click here to learn more about pre-harvest drop management.

More than two decades ago, researchers in Michigan determined that there there are an average of 143 days between full bloom and the first commercial pick of Red Delicious apples that are to be held in controlled atmosphere storage (i.e., firmness between 17-18 lbs; starch between 2.5-4 on the 8-pt scale Cornell Starch Chart). Additional seasonal adjustments above or below the average number of days until harvest are made based upon the average daily minimum temperatures for the 15 days after full bloom.

For the past several seasons I have tested the Michigan model using fruit from a block of Bisbee Red Delicious on MARK rootstock. Results to date have shown that this model is very good at predicting harvest maturity in Virginia.

Based on the Michigan model, here are the predictions for 2014:

In Winchester, Bisbee Red Delicious full bloom was April 27 and average minimum temperature for the 15 days after full bloom was 0.5°F more than 50°F. Using this data in the Michigan model, harvest is predicted to be 143 days after full bloom. This puts the predicted harvest date for the first CA pick of Red Delicious at September 16.

In Central Virginia (Tyro), full bloom for Red Delicious was estimated to be April 20 and the predicted harvest is September 9.

If you want to compare the model to your own situation, here are the previous years’ predicted harvest dates:

2011 Winchester: September 10
2012 Winchester: August 26
2012 Central VA (Batesville): August 25
2013 Winchester: September 18
2013 Central VA (Piney River): September 15

Since most growers have Red Delicious trees in their orchards, other cultivars (and strains of Red Delicious that ripen earlier than Bisbee) can be estimated based upon experience on their picking date relative to Red Delicious.

Another method for estimating harvest date uses the rule-of-thumb that says, “for each 2-3 days departure for the normal bloom date, there will be a one-day departure from the normal harvest date.” (Blanpied and Silsby, 1992).

You can find more information about harvest maturity indices in this post.

Starting in August, I will start conducting maturity evaluations of fruit from the Winchester AREC and surrounding orchards.

References

Blanpied, G. and K. Silsby. 1992. Predicting Harvest Date Window for Apples. Cornell Information Bulletin 221. <<pdf>>

Beaudry, R., P. Schwallier, and M. Lennington. 1993. Apple Maturity Prediction: An Extension Tool to Aid Fruit Storage Decisions. HortTechnology 3(2): 233-239.

MaluSim Carbohydrate Model for May 27, 2014

Posted on May 29, 2014 by Greg Peck

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.

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

Posted on May 22, 2014 by Greg Peck

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:

ethephon (0.5 -1.5 pints/100 gal)
ethephon + carbaryl (1 pint)
ethephon + carbaryl + oil (1 quart)
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 19, 2014

Posted on May 20, 2014 by Greg Peck

On Monday, I ran the MaluSim model for Winchester and a season recap for the Central Virginia region.

For the Winchester area, the carbohydrate status has been in the -20 to 20 g CHO/day range since May 15. This means that thinning sprays made between last Thursday and today are predicted to have an average response. For the next couple of days, the model is showing a significant carbohydrate deficit. This is being caused by the cloudy weather that is predicted, as neither day nor night temperatures are forecast to be very high. Cloud cover remains the hardest variable to forecast. If the next two days are sunnier than forecast, or if the rain showers occur at night, then I would not expect the actual carbohydrate balance to go into such a low deficit. However, if the weather forecasts that I used in the model are accurate, then growers should avoid thinning on Wednesday. Either way, the best predictor of the potency of chemical thinners is the 2 days before, day of, and 3 days after (2+4-day) running average (the black line). As you can see, the running average remains between 0 and 20 g CHO/day, meaning that chemical thinners will have an average response.

For the Central Virginia region, I’ve run a recap of the season using weather station data through Monday, May 19. Growers should compare their thinning results to the carbohydrate status at the time they made their application to see how well the model predicted the potency of thinners this year. From my experience, using the MaluSim model as a forensic tool can really help explain why chemical thinners work so differently from one year to the next. As I repeatedly have said, the most difficult part of using the MaluSim model to make real time decisions is having accurate weather data to use as inputs. As I mention above, cloud cover can really impact the carbohydrate status in the tree, and thus the responsiveness of thinners, but it is the hardest variable to forecast. Additionally, weather can be very local. We experienced this issue with the major differences between Tyro and Piney River weather forecasts. We also saw a lot of variable temperature data, with several days between May 8 and 14 being 5 or more degrees Fahrenheit warmer than forecast.

Even with these issues, I hope that the model is providing useful information that helps you make sound management decisions. If you have any feedback, please don’t hesitate to contact me.

I will continue to run the Winchester model until fruit size is too big to thin with NAA and 6-BA.

Download the full reports:

Central VA MaluSim 5_19_14

Winchester VA MaluSim 5_19_14

MaluSim Carbohydrate Model for May 15, 2014

Posted on May 15, 2014 by Greg Peck

Fruit in the Winchester area is at the ideal size for chemical thinning.

Thinning applications made on Monday through Wednesday of this week will likely see an excessive amount of thinning, especially if fruit was 8-12 mm in diameter. Thinners that were applied on Thursday will likely have a moderate to strong response. Thinners applied Friday (if it stops raining!) through the weekend will have a normal to weak response. If the weather forecast holds, growers should consider slightly increasing rates and using a surfactant for thinning applications made over the weekend. I’ll run another MaluSim model on Monday.

Table 1. Fruitlet sizes (mm) at the Alson H. Smith, Jr. AREC in Winchester.

Variety	12-May	15-May
Empire	10.4	12.2
Fuji	7.0	9.0
Gala	8.7	11.3
Goldens	8.0	9.5
Idared	8.1	9.5
Pink Lady	9.2	11.0
Red Delicious	8.0	10.1
York	7.9	10.7

Download the full Winchester report:

Winchester VA MaluSim 5_15_14

Fruit in the Central Virginia region is now beyond the size where chemical thinning with 6-BA or NAA is effective. If additional thinning is needed, growers should use ethephon. While these late or “rescue” thinning applications are not very responsive to the carbohydrate status modeled with MaluSim, ethephon does tend to be more active when applications are made on hot days. I will run a season recap for the Central Virginia region in a few days (I was having technical issues accessing the weather station data).