Attached 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.
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.
In 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:
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
The 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:
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:
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:
For more information, download pdfs of the models:
MaluSim models were run on Monday May 6 for Winchester and Central Virginia (Piney River). The outputs from both locations were fairly similar, with carbohydrate deficits predicted over the next six or so days. This is mostly due to the cloud cover from a series of storms that will pass through the region. With sunnier conditions and warmer temperatures, the model predicts a carbohydrate surplus by Saturday.
Apple trees are still at late bloom to 4 mm fruitlet size in the Winchester area, and growers will probably not need to start thinning until later in the week or early next week.
In Central Virginia, fruitlets are ranging from 8 to 15 mm. Growers should consider reducing rates over the next few days as the model is predicting an aggressive response to standard rates of chemical thinners. However, as we move towards the end of the week, growers should use full rates to ensure an effective response.
It is unclear how much “natural” thinning will occur from this prolonged stretch of cloudy weather. However, work by Dr. Byers suggests that 3 days of cloudy weather with temperatures at 70F (this was a controlled study in growth chambers) can cause 50% of the fruitlets to abscise. With the prolonged stretch of cloudy weather that we are experiencing, growers should consider being less aggressive with rates until the end of the week.
Today, I ran the first MaluSim Carbohydrate models for 2013. This includes a simulation for Winchester, and a simulation for Central Virginia (Piney River, VA). Thanks to Bennett Saunders for sending us the data to use for Central Virginia.
The Malusim model was developed by Drs. Alan Lakso and Terence Robinson at Cornell University to estimate the carbohydrate balance in an ‘Empire’ apple tree based upon many years of detailed research and information found in the scientific literature. In recent years, the model has been used by researchers and extension specialists in New York as a tool to help assess the application timing for applying thinning materials at the 10 mm fruitlet size. Carbohydrate status, and therefore the MaluSim model, is not as important for other times when chemical thinners might be applied (i.e., bloom, petal fall, 20 mm), so it is not as clear how well the model does to predict the response of chemical thinners used at timings other than 10 mm.
For the past several years, I have been running trials at the Winchester AREC to see how well the MaluSim model performs under conditions found in Virginia. Many researchers, including myself, are still working towards understanding the best way to use the model. From what we have found, when weather forecasts are used to predict the future carbohydrate status of an apple tree, the MaluSim model can provide a warning as to when there might be a chance for severe under- or over-thinning. This is particularly true when there are three- or four-day trends with large carbohydrate surpluses or deficits predicted. For this reason, in addition to the data points for each day, I show a four-day running average (the black line on the charts). To be consistent with other researchers and extension specialists, the four-day running average is calculated from the date the data is show to three days into the future.
Please keep these caveats in mind if you are using the MaluSim model to guide your thinning application timing:
In the below pdf files, I provide a chart of the weather data that are used to run each model (daily maximum temperature, daily minimum temperature, and daily solar radiation), a chart of the MaluSim model with day-by-day data and a four-day running average, and a chart with the potential response a chemical thinner might have for different levels of carbohydrate balance in the tree.
So, what do today’s models show? Some very advanced blocks of early blooming apple cultivars in Central Virginia are getting close to the 10 mm thinning stage. From applications that occur today and tomorrow, you should expect “normal” to “slightly aggressive” response from your standard thinning rates, but nothing that suggests sever overthinning. However, there is a period of unsettled weather predicted for Mon-Wed of next week that could cause the carbohydrate levels to drop in the trees. It all depends on the amount of cloud cover we get over those days. Temperatures are going to remain moderate over that period, so even with the potential for some cloud cover, it doesn’t look like a severe carbohydrate deficit. Cloud cover is the hardest thing to predict, and predictions are only good for 3 days at best.
In Winchester, we are still at late bloom to petal fall, so there’s probably another week before the carbohydrate model data needs careful interpretation.
I will talk more about the model at tonight’s In-depth fruit school in Winchester.
Here is the final MaluSim simulation for 2012 (pdf). Please let me know if you have any questions or feedback.
Also, we’re starting to see larger (+25 mm) fruit coming off of apple trees. Some of this fruit is abscising as a result of chemical thinning, but there also appears to be fruit that had either poor pollination (not all carpels have seeds) or had seeds that started to grow but died soon thereafter, possibly as a result of freeze damage. As you monitor your blocks for thinning responses, make sure to cut into the fruitlets and look at the seeds. Many of the fruitlets that have damaged or missing seeds are falling off the trees at the same time as those that were chemically thinned.
Today’s MaluSim simulation for Winchester (pdf) confirms that the cloudy weather from the cold front that hung over the region for the past few days caused a carbohydrate deficit. The deficit was somewhat less severe than originally predicted, but resulted in similar enough data that I would not have changed the interpretation I provided on Monday. The difference in the predicted and the actual data was due to cooler daily max temps and more solar radiation than forecasted. As I’ve mentioned previously, cloud cover forecasts are the least accurate and the most difficult to interpret.
Over the coming weekend, the model is showing a period of carbohydrate surplus, then another storm system is predicted for next week, which could cause another carbohydrate deficit.
On Monday, I will run the MaluSim model one last time for this season so that you can have a final version to reflect on as you assess the thinning in your orchards. Please provide me with feedback on how you used the model this season. Did it predict what you are seeing in your orchards? I would appreciate any comments that you think would be useful for improving the model for future years.
Today’s MaluSim simulation (pdf) confirms last week’s forecasts for a mild carbohydrate deficit over the past weekend. Even though cooler temperatures are predicted for this coming week, several days of cloudy weather are showing the potential for a very severe carbohydrate deficit starting tomorrow (Tuesday). If we get less cloud cover than predicted, I would expect less of a carbohydrate deficit. Nonetheless, those who are still applying chemical thinners should be cautious about rates and timings during the coming week, especially in blocks with already reduced crop loads due to frosts. The model is predicting a less severe deficit towards the end of the week and for next weekend (if you believe long-term forecasts). As I mentioned last week, we are not sure how well the MaluSim model predicts thinning with ethephon-based materials.
As a reminder, there will be a Rappahannock County in-orchard meeting on Wednesday at Lee’s Orchard and a Morning Update meeting on Thursday at the AREC.
