Click on this link to see the MaluSim simulation for April 30, 2012 (pdf). As I’ve mentioned previously, it is recommended to look for three-day trends in carbohydrate balance. My colleagues in New York who have been working with the MaluSim for several years now have suggested using a multi-day running average carbohydrate balance, as opposed to the day-by-day data that I have been presenting. Within the file, the first simulation chart is for the day-by-day data, and the second simulation chart is for the three-day running average. The running three-day average is meant to smooth out the data to make it easier to see the trends. Since I haven’t compared previous years’ thinning efficacy using a three-day average, I am less familiar with how to interpret the numbers. Nonetheless, if you look at either the day-by-day data or the three-day running average data, you’ll see that we’re heading into a period of carbohydrate deficit. This means that your chemical thinners will have average to slightly aggressive activity if applied tomorrow (Tuesday) through Thursday.

As a reminder, the model is based on an idealized Empire apple tree that has an average crop load, average number of extension shoots, and has not had any other stress related damage (e.g. frost). Therefore, the model is only meant as a guide for understanding the effects of weather on the activity of your chemical thinners. You should base your thinning applications on the crop situation in your blocks, as well as your experience.

Most cultivars at the AREC are at or beyond the 10 mm fruitlet size. Although  differential separation between fruitlets is not extreme this year (especially in clusters with no king bloom due to the frost), it is still assumed that weaker fruit will be thinned more easily than stronger (i.e. larger) fruit. Since there is a great amount of variability in fruitlet sizes within trees and within orchards, make sure to properly assess blocks before applying chemical thinners.

Please let me know if you have any questions. You can use the comments feature on this blog site, or send me an email at greg.peck@vt.edu.

As a final note to today’s post, I want to thank Drs. Alan Lakso and Terence Robinson from Cornell University who have spent many years working on developing the MaluSim model. They have been very generous in sharing the model and their experiences interpreting the model for use in predicting thinning efficacy.