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

Fruitlets in the Central Virginia area are quickly sizing up (reports are in the 12-18 mm range), and growers have only a couple-few more days to use NAA and 6-BA products for thinning. In the Winchester area fruitlets are just entering the 10 mm thinning window, but with the hot weather over the past few days it is likely that fruit will be growing at a rapid pace (greater than 0.5 mm per day).

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

In Central Virginia, the MaluSim model is showing a moderate carbohydrate deficit for the next three days, and then the carbohydrates balance shows positive values through the weekend.  A large deficit that was predicted to occur over the past weekend never materialized, largely because there was more sunlight than forecasted. Additionally, as the expanding leaf surface transitions from being a carbohydrate sink to a carbohydrate source the model will continue to show a positive carbohydrate balance. Growers should target blocks that require more aggressive thinning on Tuesday and Wednesday at normal or slightly reduced rates (unless trying to thin larger fruit) and then target blocks with lighter starting crop loads towards the end of the week.

In Winchester, bud break was 6 days later than in Central Virginia, meaning that many leaves are still sinks for carbohydrates and more severe deficits occured over the past few days.  However, as the Winchester area enters into the thinning window, less severe carbohydrate deficits are predicted to occur. Growers should start thinning their earliest blooming cultivars on Tuesday evening or Wednesday and then move to more lightly cropped blocks towards the end of the week and over the weekend.

Click below to download the full pdf reports:

Central VA MaluSim 5_12_14

Winchester VA MaluSim 5_12_14

Due the rapidly changing weather forecasts, I ran the MaluSim model again on Thursday. For Central Virginia, the model is showing values in the -20 to 20 range for the next seven days. This means that growers should expect an “average” response from their chemical thinners.  Growers in the Central Virginia region should target the next couple-few days to make their thinning sprays as fruitlets are at the ideal size for applications of NAA and 6-BA. Fruitlets grow at ~0.5 mm/day in cool temperatures, and as you can see from the table below, up to 1 mm/day with warmer temperatures.

Table 1. Fruitlet sizes at Silver Creek Orchards.

Much warmer day and night temperatures are forecast for the Winchester area, so the MaluSim model is showing a persistent carbohydrate deficit for the next five days. However, we are still at petal fall to ~5 mm for most cultivars, so hopefully by the time fruit are at 10 mm more moderate weather conditions will reduce the chance of over thinning. Chemical thinning applications made when either the day-by-day or running average value is below -60 g CHO/day will likely result in aggressive thinning.

I will run the models again early next week. Please download the below pdf files for the full report.

Central VA MaluSim 5_8_14

Winchester VA MaluSim 5_8_14

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

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.

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.